Often, tutorials over simplify ignition timing to the point that its lead to an overall lack of understanding of how it works. for me, understanding what a system is trying to do is often my own deliverance in having a strong command of how to interface with that system. okay, so less engineer words here - if you understand how something works, you are much more effective in tuning it to peak performance. Edit: one thing I forgot to mention - when you go up in altitude, atmospheric pressure drops, so ignition timing has to increase for all things equal at sea level. Progression Ignition distributors don’t a stupendous job of handling this on the fly.
ThunderHead289. My granddad used to play with timing. He made gasoline engines work on parafin. I used to play with it a bit also. I would advance my honda 4 stroke moped a bit to get ,,performance,, of a 2hp cb 50cc block(a netherlands moped block only allowed 49,9 cc) they had an balancer unit like your mechanical timing advancer. Think jappanese: it worked the other way around. When reaching the max revs it retarded the ignition thus keeping the revs controled. I could rev my block up to 12000 instead of 8000. 2 way to block the weight. 1 some guys would put a taper trough the weight and the base plate. That was an deliberatie action. 2 block them with a strand of wire. Possibillity 3 get an german or belgian flyweel. That didnt have the counterweights. Or take public transport?
I would do a tuning tutorial for the most common thing, which is heavily worn, high mileage cars which have low compression due to wear, and therefore want more advance. That's in addition to both of mine being low compression smog motors. However, some old motors also have heavy carbon deposits, which take up space, thereby raising compression, and can get red hot, pushing ideal timing the other way, unless cleaned. I think people got the idea of deleting vacuum advance by looking at full time dragsters than hardly ever see part throttle operation. but vacuum advance does hadly any harm even to full time dragsters.
Then when you think you got it all figured out throw weather changes into the equation and fuel variations (specific gravity and rate of burn) Great explanation Luke.
Sounds like you'd need a MAP sensor for detecting pressure drop at altitude. Though you'd be getting awfully close to having a fuel injection setup at that point ;)
Yah I live at 8000 ft and have a factory high altitude 2bbl ford 2150 carb. Stickers all over engine bay stating "high elevation". Says to bump timing up 2 to 4 degrees from baseline......funny thing is that just puts the 79 motor back to an identical motors timing made in 78 before emissions on this vehicle. 79 broncos had cats and 78s did not (except California). Need to note that emissions vehicles have different timing specs than not emission vehicles so we need to "play" with things to get them right.
Luke, I appreciate that you are not a full time TH-camr. This allows you to put out only the best content. After a while, the full time guys seem to struggle to put out good stuff consistently. And you're not trying to sell us stuff we can't afford. You must be doing something right to have 200k subscribers. Thank you for all you do.
I’ve learned more from Luke than probably any other YT engine channel! Always good, no bullshit advice and clear explanation. I had a dog of a Ford 250 engine performing badly…now runs sweet as a nut after rebuilding my Holley and setting up the timing right. Thanks Luke! 👍
Thank you so much for this 'tutorial' I have learned more in 12 minutes than the rest of my life about timing. I would appreciate more of this type of video for sure!
Well said, Luke. You are one of the few that really understands ignition timing and the affects of change. The name says it all, and very few understand "Vacuum Advance". Merry Christmas and thanks for sharing.
One time I forgot to reconnect my vacuum advance after checking timing, and for the next week I was looking for fuel leaks because my fuel mileage was cut in half. I also noticed that without vacuum advance, I had to keep my foot in the throttle like halfway (almost opening the secondaries) just to stay at 65 MPH. Once I reconnected the vacuum advance, I could cruise at 65 MPH with the throttle just barely cracked open.
On a different vehicle, I finally cured an overheating issue just from switching the vacuum advance from ported to manifold vacuum source. After that it would no longer get hot while going slow and idling in traffic, and increased mileage.
I really appreciate how well spoken you are Luke. Your command of the English language helps me learn what you're teaching, much more efficiently than if you propagated the "uneducated mechanic" stereotype.
Excellent talk, in my younger days I used manifold vacuum when I should have been using venturi vacuum. Very frustrating. Mallory mechanical adv distributors were my saving grace. Good wide open throttle performance with acceptable daily driver performance.
One of the best explanations I’ve ever heard. Play it twice or three times to verify you catched everything but now a lot of stuff makes perfect sense. Thank you.
Man, whatever content you want to put out there... we will appreciate. You dropped a ton of knowledge in this video. Make them like this. No need for any crazy production and editing. Keep it real.
Thanks for posting. The younger generation needs more straight answers like these if they're getting into tuning. 4 out of 5 auto parts stores I've been to within the past few years had people that didn't even know what a cap and rotor was anymore. I personally use a timing light as well as a vacuum gauge when I set my timing. You're right about carburetors being pretty forgiving. You'll make it home, you'll just get terrible mileage until you get the tune right. That was what my car went through in high school years, haha.
Merry Christmas Uncle Luke! I have followed your Holley carb set up to the Tee! I have also followed your timing guidelines to the Tee! Result? Fantastic throttle response, no lean bogs, No rich or too lean carb issues, elect choak adjusted and proper Idle adjustment set "at choke", curb Idle adjustment on other side just slightly tweaked. No Vacuum advance on my 4160-750. MSD billet with curve kit all timing in at 2500 rpm 18 deg initial, 36 total. Thank you Luke!!!!! This car is a responsive monster at throttle whack. Cheers from Motown! Oh, Merry Christmas to your lovely wife and to all your fur babies. :)
I think I can shed a little light on the misinformation about locked out timing. The circle track guys are the ones that caused this advance lock out talk. We lock the reluctor to the distributor housing by screw and also remove all springs and advance weights. Finally we weld the rotor shaft to the driven shaft and tada! What you see on tdc with the light is what you have all the time. But we are only concerned with wot performance. This of course, will not behave well on a street engine. We typically run anywhere from 30⁰ to 36⁰ with 40⁰ being a LOT of timing. Good vids btw.
We did similar with my cousin's drag car, warm 289 with the timing locked at 38*. Honestly, aside from losing a bit of fuel economy I'm not sure it really hurt it. I expected it to be hell to start but it really isn't. He does have a gear reduction mini started though, it was designed for this.
I rember learning this from you a few years back. As I try to pass on your knowledge to others, most don't get it or ust don't belive it. You have been the most influential person for tuning ever. I thank you very much.
Wow somebody else finally knows whats going on. Nice job hard subject to teach. Like the difference between torque and HP. And there relationships it takes a little more thinking to get it right and not just someone telling you whats right. Hopefully you spurred on some thinking with the folks, good job. Spot on, hats off.
quite a good explanation...I once diagnosed a faulty vacuum advance by noticing that i manually had to advance my distributor to compensate the lack of advance at an idle, thus creating a dragging crank over while starting the engine...replacing the vacuum advance allowed proper timing and engine starting.
I'm so glad you came out of "retirement" and are producing videos again!!! I just bought a 1985 F150 4.9 St6 and am learning so much watching your videos that's helping me rebuild it. Would love some tips on getting a bit more "oomph" out of my straight 6.
If I'm not mistaken, I believe you mightve passed me on the highway one day. I was in my 77 f150 and you went and blew my doors off, haha. Awful familiar lookin blue f100. Love all these videos on carbs, ignition timing, and getting mpgs from these old school ironheads.
I do appreciate you dropping any and all info you can. Your video's have helped me tremendously, I do want to learn more but I am a pace learner, eventually I will get it. Send us video's when you can. Enjoy some time away from TH-cam, you got a life to live too.
I'm fairly good with this stuff already , and have heard and seen tons of vids and explanations but this was a great simple explanation that actually helped me understand it even better.
Absolutely incredible video and explanation. This is one of those videos they make you watch in school because it's way better than something the actual teacher can explain haha
A good way to understand is to look at a modern cars ignition map. It’s axis will be engine speed and engine load. Then look at the trends: timing goes up with speed and timing goes down with increased load. Engine speed is straightforward and easy to grasp, engine load is easy to understand too, but it does have a lot of contributing factors to consider both from a physics perspective and a practical mechanical perspective.
Yes, absolutely correct information, guy! And I would like to thank you for the videos too! You're da best! ¡Sí, información absolutamente correcta, guyo! ¡Y me gustaría agradecerte por los videos también! ¡Eres lo mejor!
I'm glad I'm not an engineer and have to think so hard about stuff. I've been hooking the vacuum advance to ported vacuum and timing it by ear for years lol
As can I. But where that gets you into trouble is when your ear tells you to add timing at idle, but now your at like 50 degrees total unknown to you. And ope, now u have a hole in your piston and your blaming “bad parts” or the “engine builder”
Ive always had luck tuning carbs , been doing it for a very long time... i never over advance carb motors, they tend to diesel when you turn them off...so by pulling a little timing, you can increase torque, while keeping your car from dieseling. Im talking about tuning an engine with low compression, naturally aspirated, . I agree with you, I think the proper way to time an engine is to indicate the crank, start with a baseline and listen to your machine, drive it, learn .
Seriously yall, listen to this guy. my truck ran like shit doing it the "oldschool" word of mouth way id heard growing up. runs like a hot damn now and starts in the hot, cold, turn key, give it a few seconds, drive away.
I’ve put together some pretty aggressively cammed small block Chevies for street use and used a locked out distributor around 40 to 42 degrees of advance but starting can be a royal pain. Using a vacuum advance though if it is set up for 8 degrees you can set the timing for 32 then when you start it and tgere’s no vacuum it’s starting at 32 then once it starts it idles at 40 this clears up a lot of issues with a rich idle with a radical cam then when you stomp on it and the vacuum goes away the mechanical weights take over keeping the timing where you want it. Distributor recurve kits have springs and weights so you can achieve this . Weights determine the amount of timing added to the initial and the springs determine what rpm it comes in. Lighter spring the sooner it comes in.
@@auteurfiddler8706 locked out distributors do not have any advance, vacuum or mechanical. Common practice for a circle track or drag car but not so great on the street because of hard starting issues. I have run a few this way on the street but they were pretty rowdy small blocks with big heads , high compression and very aggressive cams . The last one was a 420 cubic inch sbc with 13:1 compression and a 600 lift solid roller cam , 4500 stall converter , built th400 reverse shift pattern trans brake, 9” rear with 4.88 gears all in a 1980 Malibu 4 door street race sleeper. My current build is a more mild small 355 maybe stroke it to 364” gm block, forged bottom end crank, rods and pistons, around 11:1 compression, 204 cc intake runner aluminum heads with 2.05/1.60 valves etc should be about 550 hp all motor and plan on a 200 shot of nitrous on a progressive controller. Just need to find a cheap car to put it in. It will probably also use a locked out distributor but with some kind of electronic ignition box like an msd so I can set up timing retard for he nitrous it can also retard the timing for start up.
@@auteurfiddler8706 i miss understood your questions. Yes it idles at 40 degrees on vacuum advance then as the throttle opens the vacuum drops but by then the rpm should be high enough to bring the mechanical advance weights into effect to maintain the timing. How soon the centrifugal/mechanical comes in is adjusted by changing springs on the mechanical weights, how much timing is determined by the weights and their shape.
@@olekdah definitely not a gas sipper lol. Probably less than 10 mpg I ran a 950 cfm Dominator on it. The bottom end was made up of used sprint car parts including tge Dart block.
Ignition timing has a lot to do with the resonant condition of maximum power. It's like a swing where you kick your legs out is like the spark. Where you advance the spark timing, there's more time to develop horsepower at higher rpms. Where you go over the top of the swing-set is like your horsepower peak. The timing of the legs kicking is just like variable ignition timing across the rpm range. Less advance at slower speeds and higher advance at high speeds. Compression ratio is the real source of all power. Ignition timing is just to fine tune all the performance that is really available out of the engine to the wheels.
I have an FE that would get hot unless I was moving pretty good. Threw some more timing at it and never had that problem again. Doesn't even get to the middle of my temp gauge ever.
I gave up on vacuum or mechanical advance 30yrs ago.....I understand more timing is a good thing when idling around, locking out the stock dizzy and using manifold vacuum to add timing when driving around worked but it was completely a gas mileage thing. Who was driving there 450hp mustang nice enough to find out...lol
Good stuff Luke... Refreshed alot of what i forgot 20 years ago haha. Congrats on 200k Brother... You earned it.. Looking forward to see more videos coming out soon. Hope you and the family have a wonderful Christmas holiday.
To make performance you have to light the fire well before TDC, as do all manufactures. Usually somewhere between 28- 38 degrees before. That is maximum advance ofcourse, the distributor [or computer] has to ramp it in usually from around 10 degrees at idle. Maximum adavance will always be in before max 3500. Many race engines however simply do not use an advance curve because the engine is say turning 3500-7000rpm. Simply lock the distributor. Though in that application have a start button that cranks the engine to A get oil pressure and fuel before you actually turn the ignition on. Or they will on occasion fire against themselves Vaccuum advance is there for two things, it stops surging on constant throttle which in turn helps with economy. That is IF ofcourse if you have vaccuum. Many modiified engines have very little. If any! And Holley HPs have no provision for vaccuum advance! Or vaccuum brake boosters either. For a race engine it is a waste of time and can cause grief. For a true street car engine even modified it makes the car drive smoother. All engines, especially older ones on unleaded fuels will benefit from a multi spark ignition. Several brands, none are bad and the basic ones are perfectly fine on a stock or near stock family car engine. They start better, idle and run smoother. Use less fuel. Unleaded lacks volatility and really benefits from the better ignition. You can sometimes creep a little more advance in as well.
My dad loved the 2 barrel carb on anything. A Pontiac , Chevy Caprice/Impala kinda guy. His favorite small block was the Chevy 267 or 4.4 liter. Or 318 Dodge 2 barrel.
Dynamic 🧐 I'm pretty sure you mean corrected. Dynamic takes into account way more than just IVC. I use my own calculator. Bore Stroke RL HGT CH vol. DH front to rear PD TRL PDV CT Altitude Degree Offset I'm always within 2.5 PSI and always spot on with Stc and Cor. I like your videos 👍👍 keep up the good content 🙂
Very educational, appreciate the simple yet to the point explanation. I do have a scenario to run by you though; what would literally cause absolutely no vacuum signal at the timed spark port regardless of throttle position? I can apply pressurized air to the barb on the side of the primary metering block and air comes out through the passenger primary barrel/venturi (no obstruction through the passage). 76 F250 300 i6 (stock longblock), clifford intake, holley 4150 (list 6390-1) 450 cfm. Engine produces 20 inched of vacuum at idle. Would really like to be able to utilize the vacuum advance setup as described in your videos, but this one has me stumped...
THANK YOU for this! wow, I can't tell you how many times I've come across people totally destroying carburetors because of this very thing. I mean it's gotten so bad I don't even look at Swap Meet carbs anymore (esp Eddies that come with the "tune kit"). They've been taken so far out of base line, & DIY drilled that it's not worth it to me anymore to try and reset them. Why did they do all this? Exactly what you show right here. It's the Distributor not the Carb. But now with the DIY InnerNet, I'm finding this in used distributors as well. Much easier to just buy new ones, with a set base line you know, and go from there on either of the 2.
Probably the best description of the process. Its amazing how long the burn time can be (& then piston speed, long vs. short stroke, higher rpm...), lol. It definitely will give folks a better basis to understanding the multiple burst injectors they're researching for economy & performance (much like the high hp diesel tech.). Thanks!
A couple years ago in one of your ignition tutorials you mentioned the Progression Ignition fully computerized ignition but, as far as I know, never followed up on this. Well, based on your comments I installed one in my 65 GTO. It's powered by a 406 smallblock Chevy with Dart aluminum heads, Howard roller cam with 10 in. Hg. vacuum at idle, Edelbrock Performer RPM Airgap intake and Summit 750 vac secondary carb (also based on your advice). Compared with a conventional distributor the Progression is like a carb vs. EFI. You can focus on specific aspects of engine operation and really improve performance. Specific areas are idle quality, idle when the a/c kicks on, off idle acceleration as the clutch is released, transition from idle circuit to main jet acceleration, the possibilities are endless. It would be interesting for you to pick up a Progression distributor and play with it in one of your vehicles.
I’ve installed a couple of them for people as well as have two of my own. I haven’t worked on the supercharged 65 for a couple of years due to life changes and moving. Should have it out the spring, where it will have a progression unit. I met Ted when his company was basically brand new. Really great down to earth guy who was annoyed with the typical limitations, so he did something about it. He gifted me a couple of them for helping him get his name out there. Really looking forward to finally using my own
@@ThunderHead289 That's great to hear. I hope that some day you'll do a deep dive on setting up the timing map. I studied some Holley Sniper maps to get an idea of what a fully computerized map looks like. What is also really cool is you can open the edit table while driving and see what the advance is doing under various scenarios.
The terminology has changed in recent years. We used to talk about degrees advanced or degrees retarded, but now gearheads have compressed that into jargon about more or less "timing." Go back to talking about advancing the timing a few degrees, backing it off a few degrees, or retarding the timing a few degrees, and it makes much more sense to guys trying to figure it out. Saying an engine needs more timing is like saying a stereo needs more tone, or saying the engine needs more tune. It doesn't make sense unless you're in on the jargon and know exactly what you mean when you say "timing."
I have a statement for those trying to apply the information. Degrees in relation to advance, I struggled with. Vacuum advance the number gets higher because more advance is less timing. (It sounds silly to say now, but when I was still wrapping my head around this i always thought bigger number=more timing.)
Do you mean "Vacuum advance the number gets higher", as in -10 is a higher number than -20. Greater vacuum, as in -20 is more vacuum than -10, gives more advance and more timing as @Don Denny says. At WOT(full throttle) vacuum drops to zero and gives no additional vacuum advance at all.
Late timing leads to hot exhaust gases which transfer a lot of heat to the cylinder head on the way out. If you get your timing late enough you can make the manifolds glow.
Back in the 1980s, I had late 1960s cars that were subject to California Smog Laws. Living in Sacramento, I had to disconnect the vacuum advance line and cap the ports. Timing had to be set to a certain setting. Last was a sticker had to be placed under the hood somewhere visible.
Long story short get rid of that old school junk and get and get electronic ignition problem solved but Luke you're very knowledgeable on the old school stuff I have to give you credit for that I'm from the old days and I know old school stuff but the new electronic is for Superior then the old junk
Um.... electronic ignition still uses mechanical advance and vacuum advance mechanisms. Now digital advance like a progression ignition distributor is a different deal.
I have a chevy small block engine with small cam. Got it set to 800 rpm at idle. Advanced settings to 35 at tdc and 12 degrees idle at tdc. I used pressure vacuum gauge and the best reading I could get is 14. I was hoping to get it up to 16.Truck runs alot better than when I bought it. Im learning everything about cars from watching your videos and has hoping for suggestions.
Hi Luke, I’ve been watching most of your videos on ignition timing and learned a lot. Right now I’m restoring an old EFI Mercedes sl with my dad and I was wondering: how do I know if ignition timing is too much? The workshop manual 15 degrees before tdc at 3000 but that way the car is sluggish. With 35 degrees at 3000 rpm the engine feels like it has way more torque but can I get more timing or will I damage something?
15 degrees was very low. I think you are more in the right numbers with 35. Your EFI have a knock censor that pull of the timing if it gets to high I guess? Most naturally aspirated engines like a total timing of 32 to 36 degrees BTDC. What is right for your engine depends on the compression ratio and the shape of the combustion chamber. And of course your type of fuel. 10 to 16 degrees initial timing, and 18 to 22 mechanical advance is normal. And finally vacuum advance. My small block chevy 383 (6.3 L) carb engine with fast burn chambers, 10.8 compression, runs on 14 initial, 20 mechanical (max at 3000rpm) and 16 vacuum. Cruising at 3000 rpm it pulls a total of 50 degrees with A/F readings around 14.5. 15 l / 100 km or 15 Miles per gallon (USA). A rather radical camshaft for street use thou. Close to 500 hp.😃
@@olekdah thanks for the explanation. I think the manual means 15 degrees of initial advance because this way the total advance is around 34-36 degrees at 3200 rpm (plus the vacuum advance). I made the rookie mistake of setting 15 degrees of total ignition timing and that’s why the performance were extremely poor. Btw I don’t think the car has any system to decrease the amount of timing in since it has points and the efi is very old (‘72 Bosch d-jetronic)
Hey Luke, been watching you for awhile now and have a question for you Sir.. I’m amazed in that I’ve been working on a Chevy C10 with a 383 Small Block. Initially guy I’d bought it from had vacuum advance disconnected. I re-enabled it. Ran better afterwards and better when re-timed. Then I had slight spark knock, and here is the strange thing which happened.. “Before getting the timing correct, I lessened the exhaust back pressure by going to larger diameter exhaust pipe, then here is the thing… The spark knock which was in engine went away with less back pressure in exhaust. This showing dynamics you had mentioned here? Proof of your statements given I’d say, very cool Sir! Question : and for example here.. “Less exhaust back pressure eliminated this particular engine detonation or “knock?” Cool😊
Makes complete sense. I understand the whole difference between ported/manifold vacuum debate and how they work but when using ported vacuum we dont get any benefit from vacuum advance during idle. Would love to hear your thoughts on Unity Motorsports Garage theory on using adjustable vac advance can with manifold vacuum
I believe I have the highest viewed video on ported vs manifold on the Internet. Perhaps this video will help to further explain the benefits: th-cam.com/video/bUv5tUC6Ioo/w-d-xo.html If you follow along with that video, it’s extremely elementary. Just remember who the engineer is and who isn’t out there.
Hey Luke, love your videos, very informative! I have a question, why do most (if not all) jet boats have no vacuum advance? I do understand that it's because the majority of them will be ran at WOT most of the time and you're not really looking at fuel efficiency. Is there any other reason? My second question is, since there is no vacuum advance, why do a lot of people run jet boats with maxed out mechanical advance even at idle? I'm talking about 70s and 80s big block jet boats btw Thank you.
Most of them are maintained rpm well above an advance curve range (above 2800rpm) and they are usually fairly loaded (so no vacuum for a vacuum advance, and no reason to have low load advance). Couple that with the issue of the potential for moister to get into the distributor and rust up and seize the advance mechanisms, I completely understand why they don’t.
Can you do a video step by step for the grandma's out here who are teaching themselves? Basically, someone like me who is absolutely clueless, step for step. I CANNOT find an old school mechanic near me to adjust my Holley 670 truck avenger to my 454. Out of desperation I'm asking. (P.S. I enjoy your videos. Descriptions are fantastic)
In my '36 Ford lately, the vacuum advance has been making a screeching sound when the engine is running. When I disconnect the vacuum advance line, it stops making the noise. So I was going to pull the spring and piston out of the vacuum advance and try to run it by idling up the carb to counteract the having no vacuum advance stuff on it, but was also going to check and make sure nothing was bound up in the advance plate. The distributor was rebuilt before, but I'm thinking about sending it back to the rebuilder to go through it again if I can't find the source of the problem. Take a look at one of those distributors when you get the chance, it looks like a divers helmet, and has 2 distributor caps. That's what I'm trying to work with.
Sounds like it might just have a ruptured advance diaphragm and that’s what you hear whistling as air is drawn through it. Easy test is to just suck on the hose - if it’s good, you shouldn’t be able to pull air through
Vacuum works instantaneously, giving fast advance, working together with the acceleration pump squirts (carb side). As one throttles up to WOT, the vacuum advance goes max quickly and then decreases and eventually going zero (close to WOT). This is the basic idea. Centrifugal will only advance according to rpm, not helping out on the initial transient surge to start revving. This is the basic idea to have both working in tandem in the distributor. Great channel with really original stuff. Greets from Brazil.
Thunderhead289 I would like to hear your thoughts on the FE rocker arm oil restrictors. Should we use them or not? I know the FE engines have oiling problem because of the oil being pumped out of the oil pan to fast to the rocker arms. That was a major problem with the 390GT engine back in the day. I did a test with a drill on the oil pump shaft and I could pump the pan down below the screen in about 30 seconds on a 428 SCJ engine. I bought this engine as a rebuilt engine. Ended up rebuilding it again with boring it .30 over. I got stung on that buy. Lol.
Vacuum advance should be hooked to ported vacuum. Ported vacuum comes into play at light throttle/cruising speeds. This advances the timing, to advance timing even higher than centrifugal advanced timing. The purpose of this is for fuel economy. If you notice that mallory distributors do not have a vacuum advance, because they are not worried about fuel economy, just total advance at wot. When you are at light throttle, the throttle plates are open enough to allow vacuum to pass through the ported vacuum port and advance the timing. If you hook it to manifold vacuum, your timing will be too high at idle. This can cause rough idle. Hooked up properly, you should be able to get 4-5 mpg better than disconnected.
All things I have said in the past. I’m a huge promoter of ported advance. search ported vs manifold vacuum and see what your top search result is. I even show that ported in fact does drop out just like manifold at hard throttle by having a vacuum gauge hooked to both. For whatever reason folks tend to confuse venturi vacuum with ported. I always try to explain that venturi vacuum is present in the carb, it’s what actuates the vacuum secondaries.
Hi there, could you please clarify why having more advance timing ( timing too high?) at idle with a Vacuum advance is a bad thing? I have been told that throttle response would be optimized with less mechanical advance ( but faster curve) in the distributor, and a higher initial timing ( say 10 -16 degrees BTDC) for Total Timing of 30-36 degrees. Cheers
The vacuüm advance was broken on my 1975 land rover. And it noticeably decreased part throtle performance and fuel economy. I fitted a fancy bleutooth programable distributor and drives a lot better now. Its a very low perfermance engine so if its missing power its very noticeable.
@@ThunderHead289 its a 123 ignition unit. Its the same sort of distributor but the progression unit might be slightly fancier. It runs a 1000 times beter than a €40 Chinese point distributor. Thanks for al the tips on carbs and ignition over the years! Never used any of it on an American car though lol.
Excellent Content Thanks. Question? I'm struggling with understanding what "Initial Timing" Value is ideal for a given engine. (10°, 12°, 14° etc.). Would Hooking up a vacuum gauge to Manifold port and (adjusting the distributor at idle, transfer slots set correctly) achieving the initial timing by reaching (Max Vacuum, back off a tad) be a wise way to discover what initial Timing value is ideal for an engine? Thanks.
I put a Blueprint brand 383 in my fathers car and their tech said do not hook up vacuum advance. He said at high rpm's their engine breathes so much that even with the throttle plates wide open it will still have manifold vacuum and advance the total timing to much. He said with a total mechanical advance at 3500 and 32 degrees before top dead center hooking up the vacuum advance could add several more degrees and detonate.
@@ThunderHead289 The way they dyno them is unhooked. He said in most cases your way of thinking is correct, yet in this combination he said it will pull a measurable vacuum at high rpm's with the 750 cfm carb that was provided. I have no proof.
@@1958johndeere620 is just test it out personally - have a vacuum gauge in the cab and see what happens. On a 600dp I was close to that at 6000rpm on a 302 - saw vacuum gauge raise to about 1inHG. I’d be surprised if a 383 could manage that. If your happy with it, don’t change it - they just build in a safety margin for themselves, but it would improve economy. You also can’t arbitrarily say x timing for x engine. A 383 in a light camaro would sport a totally different timing curve than a truck if both tuned for peak performance
@@ThunderHead289 He actually wants me to do the same thing when I get a chance. He wants to know if in our application what it does draw. It will take a co pilot to read the gauge, gets pretty busy.
Yes....an engine with a static CR of 9:1 with a lopey high overlap cam loses cylinder pressure down low.....it'll need more initial timing to make up for lost pressure. With no vacuum advance, you'll only have initial + mechanical advance to maybe 35/36 degrees at lower rpms. (under 3000) Add vacuum advance for more timing and efficiency at lower rpm. On a small block Mopar, I have 35 degrees initial + mechanical all in @ 2,300 rpm in a heavy truck and it pulls well. No vacuum advance currently....it stopped working suddenly. Fuel mileage is terrible without it!
That chair is super squeaky - the only reason I have cuts in this video is because I managed to rotate like 0.5 of a degree which emits quite the scream from that thing. One too many gas station burritos I guess, too heavy for that poor little guy 😂
If there was no reason to ever not run a vauum advance then why do all of the various distributor manufacturers build mechanical advance only distributors? I run the MSD pro billet version and it has no vacuum advance. My set up is far from a stock engine that somebody wants to pokey around with though. Maybe you should have said to keep your vacuum advance if you have built a stock to mildly modified engine vehicle that you drive mostly on the street.
Often, tutorials over simplify ignition timing to the point that its lead to an overall lack of understanding of how it works. for me, understanding what a system is trying to do is often my own deliverance in having a strong command of how to interface with that system. okay, so less engineer words here - if you understand how something works, you are much more effective in tuning it to peak performance.
Edit: one thing I forgot to mention - when you go up in altitude, atmospheric pressure drops, so ignition timing has to increase for all things equal at sea level.
Progression Ignition distributors don’t a stupendous job of handling this on the fly.
ThunderHead289. My granddad used to play with timing. He made gasoline engines work on parafin. I used to play with it a bit also. I would advance my honda 4 stroke moped a bit to get ,,performance,, of a 2hp cb 50cc block(a netherlands moped block only allowed 49,9 cc) they had an balancer unit like your mechanical timing advancer.
Think jappanese: it worked the other way around. When reaching the max revs it retarded the ignition thus keeping the revs controled. I could rev my block up to 12000 instead of 8000. 2 way to block the weight. 1 some guys would put a taper trough the weight and the base plate. That was an deliberatie action.
2 block them with a strand of wire.
Possibillity 3 get an german or belgian flyweel.
That didnt have the counterweights.
Or take public transport?
I would do a tuning tutorial for the most common thing, which is heavily worn, high mileage cars which have low compression due to wear, and therefore want more advance. That's in addition to both of mine being low compression smog motors. However, some old motors also have heavy carbon deposits, which take up space, thereby raising compression, and can get red hot, pushing ideal timing the other way, unless cleaned.
I think people got the idea of deleting vacuum advance by looking at full time dragsters than hardly ever see part throttle operation. but vacuum advance does hadly any harm even to full time dragsters.
Then when you think you got it all figured out throw weather changes into the equation and fuel variations (specific gravity and rate of burn) Great explanation Luke.
Sounds like you'd need a MAP sensor for detecting pressure drop at altitude. Though you'd be getting awfully close to having a fuel injection setup at that point ;)
Yah I live at 8000 ft and have a factory high altitude 2bbl ford 2150 carb. Stickers all over engine bay stating "high elevation". Says to bump timing up 2 to 4 degrees from baseline......funny thing is that just puts the 79 motor back to an identical motors timing made in 78 before emissions on this vehicle. 79 broncos had cats and 78s did not (except California). Need to note that emissions vehicles have different timing specs than not emission vehicles so we need to "play" with things to get them right.
Luke, I appreciate that you are not a full time TH-camr. This allows you to put out only the best content. After a while, the full time guys seem to struggle to put out good stuff consistently. And you're not trying to sell us stuff we can't afford. You must be doing something right to have 200k subscribers. Thank you for all you do.
I’ve learned more from Luke than probably any other YT engine channel! Always good, no bullshit advice and clear explanation. I had a dog of a Ford 250 engine performing badly…now runs sweet as a nut after rebuilding my Holley and setting up the timing right. Thanks Luke! 👍
Uncle Tony and Luke always have some of the handiest info for old engines, never skip a video!
Thank you so much for this 'tutorial' I have learned more in 12 minutes than the rest of my life about timing. I would appreciate more of this type of video for sure!
Ya know I love Ford's. And you are the best " explainer " on the net about anything mechanical. Merry Christmas to y'all.😀
Well said, Luke. You are one of the few that really understands ignition timing and the affects of change.
The name says it all, and very few understand "Vacuum Advance".
Merry Christmas and thanks for sharing.
One time I forgot to reconnect my vacuum advance after checking timing, and for the next week I was looking for fuel leaks because my fuel mileage was cut in half. I also noticed that without vacuum advance, I had to keep my foot in the throttle like halfway (almost opening the secondaries) just to stay at 65 MPH. Once I reconnected the vacuum advance, I could cruise at 65 MPH with the throttle just barely cracked open.
On a different vehicle, I finally cured an overheating issue just from switching the vacuum advance from ported to manifold vacuum source. After that it would no longer get hot while going slow and idling in traffic, and increased mileage.
i like when the carb fell back and took a nap when you said, "overall engine health". great video on timing!
I really appreciate how well spoken you are Luke. Your command of the English language helps me learn what you're teaching, much more efficiently than if you propagated the "uneducated mechanic" stereotype.
Excellent talk, in my younger days I used manifold vacuum when I should have been using venturi vacuum. Very frustrating. Mallory mechanical adv distributors were my saving grace. Good wide open throttle performance with acceptable daily driver performance.
Very intelligent and informative.
And you say you're no *science guy*.
This is VERY MUCH APPLIED SCIENCE my friend.
One of the best explanations I’ve ever heard. Play it twice or three times to verify you catched everything but now a lot of stuff makes perfect sense. Thank you.
Man, whatever content you want to put out there... we will appreciate. You dropped a ton of knowledge in this video. Make them like this. No need for any crazy production and editing. Keep it real.
Thanks for posting. The younger generation needs more straight answers like these if they're getting into tuning. 4 out of 5 auto parts stores I've been to within the past few years had people that didn't even know what a cap and rotor was anymore.
I personally use a timing light as well as a vacuum gauge when I set my timing.
You're right about carburetors being pretty forgiving. You'll make it home, you'll just get terrible mileage until you get the tune right. That was what my car went through in high school years, haha.
@motortrend needs to hire this guy because he knows everything
Merry Christmas Uncle Luke! I have followed your Holley carb set up to the Tee! I have also followed your timing guidelines to the Tee! Result? Fantastic throttle response, no lean bogs, No rich or too lean carb issues, elect choak adjusted and proper Idle adjustment set "at choke", curb Idle adjustment on other side just slightly tweaked. No Vacuum advance on my 4160-750. MSD billet with curve kit all timing in at 2500 rpm 18 deg initial, 36 total. Thank you Luke!!!!! This car is a responsive monster at throttle whack. Cheers from Motown! Oh, Merry Christmas to your lovely wife and to all your fur babies. :)
I think I can shed a little light on the misinformation about locked out timing. The circle track guys are the ones that caused this advance lock out talk. We lock the reluctor to the distributor housing by screw and also remove all springs and advance weights. Finally we weld the rotor shaft to the driven shaft and tada! What you see on tdc with the light is what you have all the time. But we are only concerned with wot performance. This of course, will not behave well on a street engine. We typically run anywhere from 30⁰ to 36⁰ with 40⁰ being a LOT of timing. Good vids btw.
We did similar with my cousin's drag car, warm 289 with the timing locked at 38*.
Honestly, aside from losing a bit of fuel economy I'm not sure it really hurt it. I expected it to be hell to start but it really isn't. He does have a gear reduction mini started though, it was designed for this.
I rember learning this from you a few years back. As I try to pass on your knowledge to others, most don't get it or ust don't belive it.
You have been the most influential person for tuning ever. I thank you very much.
Always great when there's a new Thunderhead video!
Nothing really new in the video to me, but you did an awesome job explaining everything!
Love your explanations. I'm looking to finally get a carbureted engine. Been TBI and Fuel injection my whole life.
You are one of my favorite TH-camrs. Your information always helps me improve my C10
Wow somebody else finally knows whats going on. Nice job hard subject to teach. Like the difference between torque and HP. And there relationships it takes a little more thinking to get it right and not just someone telling you whats right. Hopefully you spurred on some thinking with the folks, good job. Spot on, hats off.
Thank you thank you!
quite a good explanation...I once diagnosed a faulty vacuum advance by noticing that i manually had to advance my distributor to compensate the lack of advance at an idle, thus creating a dragging crank over while starting the engine...replacing the vacuum advance allowed proper timing and engine starting.
to Uncle Luke and Aunt Emily warmest holiday wishes from a huge Canadian fan!! love the videos ! many thank yous
love your videos, and as a non gearhead, you make this understandable. thanks Luke.
For some who no longer works on his own cars this was great explanation!!! Simplify some words and you could explain it to a class of 5 graders!!!
I'm so glad you came out of "retirement" and are producing videos again!!! I just bought a 1985 F150 4.9 St6 and am learning so much watching your videos that's helping me rebuild it. Would love some tips on getting a bit more "oomph" out of my straight 6.
Every video always worth a second watching. And maybe a revisit down the road...when it gets warm out. 🥶
If I'm not mistaken, I believe you mightve passed me on the highway one day. I was in my 77 f150 and you went and blew my doors off, haha. Awful familiar lookin blue f100. Love all these videos on carbs, ignition timing, and getting mpgs from these old school ironheads.
I do appreciate you dropping any and all info you can. Your video's have helped me tremendously, I do want to learn more but I am a pace learner, eventually I will get it. Send us video's when you can. Enjoy some time away from TH-cam, you got a life to live too.
I'm fairly good with this stuff already , and have heard and seen tons of vids and explanations but this was a great simple explanation that actually helped me understand it even better.
Good ole' Uncle Luke! Keep up the awesome content bub, I'm always glad to see what your up to.
Ever since I saw him on junkyard digs I love this guy wish had teachers like that lol
Luke's Timing was impeccable. Just in Time for all the new Christmas presents people will be getting. Time to check my Timing!!
Absolutely incredible video and explanation. This is one of those videos they make you watch in school because it's way better than something the actual teacher can explain haha
A good way to understand is to look at a modern cars ignition map. It’s axis will be engine speed and engine load. Then look at the trends: timing goes up with speed and timing goes down with increased load. Engine speed is straightforward and easy to grasp, engine load is easy to understand too, but it does have a lot of contributing factors to consider both from a physics perspective and a practical mechanical perspective.
Yes, absolutely correct information, guy! And I would like to thank you for the videos too! You're da best! ¡Sí, información absolutamente correcta, guyo! ¡Y me gustaría agradecerte por los videos también! ¡Eres lo mejor!
I'm glad I'm not an engineer and have to think so hard about stuff. I've been hooking
the vacuum advance to ported vacuum and timing it by ear for years lol
As can I.
But where that gets you into trouble is when your ear tells you to add timing at idle, but now your at like 50 degrees total unknown to you.
And ope, now u have a hole in your piston and your blaming “bad parts” or the “engine builder”
Best explanation I've ever heard on vacuum advance.
Merry Christmas & welcome back!!👍👍🇺🇸🇺🇸
Very nice explanation, thank you. Also Skorned is so awesome thanks for introducing me to them. They scratch my 90s itch
I consider you ....the Einstein...of Carburetors....no one I know holds and can teach that info the way you do...bravo.....
Ive always had luck tuning carbs , been doing it for a very long time... i never over advance carb motors, they tend to diesel when you turn them off...so by pulling a little timing, you can increase torque, while keeping your car from dieseling. Im talking about tuning an engine with low compression, naturally aspirated, .
I agree with you, I think the proper way to time an engine is to indicate the crank, start with a baseline and listen to your machine, drive it, learn .
With everything going to electronic ignition it’s good to get a refresher course on this it helps keep the mind fresh.😁😁👍👍
Going? They're long gone at this point haha.
I think these workbench side chats with Cousin/Uncle Luke are my favorites.
Great explainition as per usual this is the reason why I'm still subscribed to your channel Luke.
Seriously yall, listen to this guy. my truck ran like shit doing it the "oldschool" word of mouth way id heard growing up. runs like a hot damn now and starts in the hot, cold, turn key, give it a few seconds, drive away.
Thanks buddy, I’m only trying to help folks - yet I endure quite a degree of hostility. Funny.
I’ve put together some pretty aggressively cammed small block Chevies for street use and used a locked out distributor around 40 to 42 degrees of advance but starting can be a royal pain. Using a vacuum advance though if it is set up for 8 degrees you can set the timing for 32 then when you start it and tgere’s no vacuum it’s starting at 32 then once it starts it idles at 40 this clears up a lot of issues with a rich idle with a radical cam then when you stomp on it and the vacuum goes away the mechanical weights take over keeping the timing where you want it. Distributor recurve kits have springs and weights so you can achieve this . Weights determine the amount of timing added to the initial and the springs determine what rpm it comes in. Lighter spring the sooner it comes in.
It idles at 40???? 40 degress on the crank? Are you saying you have vacuum advance but no centrifugal advance??? It it ported or manifold.
@@auteurfiddler8706 locked out distributors do not have any advance, vacuum or mechanical. Common practice for a circle track or drag car but not so great on the street because of hard starting issues. I have run a few this way on the street but they were pretty rowdy small blocks with big heads , high compression and very aggressive cams . The last one was a 420 cubic inch sbc with 13:1 compression and a 600 lift solid roller cam , 4500 stall converter , built th400 reverse shift pattern trans brake, 9” rear with 4.88 gears all in a 1980 Malibu 4 door street race sleeper.
My current build is a more mild small 355 maybe stroke it to 364” gm block, forged bottom end crank, rods and pistons, around 11:1 compression, 204 cc intake runner aluminum heads with 2.05/1.60 valves etc should be about 550 hp all motor and plan on a 200 shot of nitrous on a progressive controller. Just need to find a cheap car to put it in. It will probably also use a locked out distributor but with some kind of electronic ignition box like an msd so I can set up timing retard for he nitrous it can also retard the timing for start up.
@@auteurfiddler8706 i miss understood your questions.
Yes it idles at 40 degrees on vacuum advance then as the throttle opens the vacuum drops but by then the rpm should be high enough to bring the mechanical advance weights into effect to maintain the timing. How soon the centrifugal/mechanical comes in is adjusted by changing springs on the mechanical weights, how much timing is determined by the weights and their shape.
@@AndyGeesGarage 😁I would like to know the fuel consumption on your 420! Or not!!😅 But I guess the fun factor overcomes that?😄
@@olekdah definitely not a gas sipper lol. Probably less than 10 mpg I ran a 950 cfm Dominator on it. The bottom end was made up of used sprint car parts including tge Dart block.
Ignition timing has a lot to do with the resonant condition of maximum power. It's like a swing where you kick your legs out is like the spark. Where you advance the spark timing, there's more time to develop horsepower at higher rpms. Where you go over the top of the swing-set is like your horsepower peak. The timing of the legs kicking is just like variable ignition timing across the rpm range. Less advance at slower speeds and higher advance at high speeds. Compression ratio is the real source of all power. Ignition timing is just to fine tune all the performance that is really available out of the engine to the wheels.
I have an FE that would get hot unless I was moving pretty good. Threw some more timing at it and never had that problem again. Doesn't even get to the middle of my temp gauge ever.
I gave up on vacuum or mechanical advance 30yrs ago.....I understand more timing is a good thing when idling around, locking out the stock dizzy and using manifold vacuum to add timing when driving around worked but it was completely a gas mileage thing. Who was driving there 450hp mustang nice enough to find out...lol
Good stuff Luke... Refreshed alot of what i forgot 20 years ago haha.
Congrats on 200k Brother... You earned it..
Looking forward to see more videos coming out soon.
Hope you and the family have a wonderful Christmas holiday.
To make performance you have to light the fire well before TDC, as do all manufactures. Usually somewhere between 28- 38 degrees before. That is maximum advance ofcourse, the distributor [or computer] has to ramp it in usually from around 10 degrees at idle. Maximum adavance will always be in before max 3500.
Many race engines however simply do not use an advance curve because the engine is say turning 3500-7000rpm. Simply lock the distributor. Though in that application have a start button that cranks the engine to A get oil pressure and fuel before you actually turn the ignition on. Or they will on occasion fire against themselves
Vaccuum advance is there for two things, it stops surging on constant throttle which in turn helps with economy. That is IF ofcourse if you have vaccuum. Many modiified engines have very little. If any! And Holley HPs have no provision for vaccuum advance! Or vaccuum brake boosters either.
For a race engine it is a waste of time and can cause grief. For a true street car engine even modified it makes the car drive smoother.
All engines, especially older ones on unleaded fuels will benefit from a multi spark ignition. Several brands, none are bad and the basic ones are perfectly fine on a stock or near stock family car engine. They start better, idle and run smoother. Use less fuel. Unleaded lacks volatility and really benefits from the better ignition. You can sometimes creep a little more advance in as well.
My dad loved the 2 barrel carb on anything. A Pontiac , Chevy Caprice/Impala kinda guy. His favorite small block was the Chevy 267 or 4.4 liter. Or 318 Dodge 2 barrel.
Nicely done!
And we have our Uncle Luck now!
Dynamic 🧐
I'm pretty sure you mean corrected. Dynamic takes into account way more than just IVC.
I use my own calculator.
Bore
Stroke
RL
HGT
CH vol.
DH front to rear
PD
TRL
PDV
CT
Altitude
Degree Offset
I'm always within 2.5 PSI and always spot on with Stc and Cor.
I like your videos 👍👍 keep up the good content 🙂
This was a great video. I need to check my timing on my F817G Waukesha motor with distributors.
Very educational, appreciate the simple yet to the point explanation. I do have a scenario to run by you though; what would literally cause absolutely no vacuum signal at the timed spark port regardless of throttle position? I can apply pressurized air to the barb on the side of the primary metering block and air comes out through the passenger primary barrel/venturi (no obstruction through the passage). 76 F250 300 i6 (stock longblock), clifford intake, holley 4150 (list 6390-1) 450 cfm. Engine produces 20 inched of vacuum at idle. Would really like to be able to utilize the vacuum advance setup as described in your videos, but this one has me stumped...
Very well said Luke @ThunderHead289
THANK YOU for this! wow, I can't tell you how many times I've come across people totally destroying carburetors because of this very thing. I mean it's gotten so bad I don't even look at Swap Meet carbs anymore (esp Eddies that come with the "tune kit"). They've been taken so far out of base line, & DIY drilled that it's not worth it to me anymore to try and reset them. Why did they do all this? Exactly what you show right here. It's the Distributor not the Carb. But now with the DIY InnerNet, I'm finding this in used distributors as well. Much easier to just buy new ones, with a set base line you know, and go from there on either of the 2.
Probably the best description of the process. Its amazing how long the burn time can be (& then piston speed, long vs. short stroke, higher rpm...), lol.
It definitely will give folks a better basis to understanding the multiple burst injectors they're researching for economy & performance (much like the high hp diesel tech.). Thanks!
A couple years ago in one of your ignition tutorials you mentioned the Progression Ignition fully computerized ignition but, as far as I know, never followed up on this. Well, based on your comments I installed one in my 65 GTO. It's powered by a 406 smallblock Chevy with Dart aluminum heads, Howard roller cam with 10 in. Hg. vacuum at idle, Edelbrock Performer RPM Airgap intake and Summit 750 vac secondary carb (also based on your advice). Compared with a conventional distributor the Progression is like a carb vs. EFI. You can focus on specific aspects of engine operation and really improve performance. Specific areas are idle quality, idle when the a/c kicks on, off idle acceleration as the clutch is released, transition from idle circuit to main jet acceleration, the possibilities are endless. It would be interesting for you to pick up a Progression distributor and play with it in one of your vehicles.
I’ve installed a couple of them for people as well as have two of my own.
I haven’t worked on the supercharged 65 for a couple of years due to life changes and moving.
Should have it out the spring, where it will have a progression unit.
I met Ted when his company was basically brand new. Really great down to earth guy who was annoyed with the typical limitations, so he did something about it.
He gifted me a couple of them for helping him get his name out there.
Really looking forward to finally using my own
@@ThunderHead289 That's great to hear. I hope that some day you'll do a deep dive on setting up the timing map. I studied some Holley Sniper maps to get an idea of what a fully computerized map looks like. What is also really cool is you can open the edit table while driving and see what the advance is doing under various scenarios.
The terminology has changed in recent years. We used to talk about degrees advanced or degrees retarded, but now gearheads have compressed that into jargon about more or less "timing." Go back to talking about advancing the timing a few degrees, backing it off a few degrees, or retarding the timing a few degrees, and it makes much more sense to guys trying to figure it out. Saying an engine needs more timing is like saying a stereo needs more tone, or saying the engine needs more tune. It doesn't make sense unless you're in on the jargon and know exactly what you mean when you say "timing."
Thanks for the great explanation! Definitely overlooked often
I have a statement for those trying to apply the information. Degrees in relation to advance, I struggled with. Vacuum advance the number gets higher because more advance is less timing.
(It sounds silly to say now, but when I was still wrapping my head around this i always thought bigger number=more timing.)
The higher the number - the more degrees before top dead center the spark plug fires.
Do you mean "Vacuum advance the number gets higher", as in -10 is a higher number than -20. Greater vacuum, as in -20 is more vacuum than -10, gives more advance and more timing as @Don Denny says. At WOT(full throttle) vacuum drops to zero and gives no additional vacuum advance at all.
Thanks for the lesson uncle Luke, you've helped me understand and congrats on the 200k subs!🤟⚡🍾
Really good video. Cleared up a lot of the mystery for. Thanks
Late timing leads to hot exhaust gases which transfer a lot of heat to the cylinder head on the way out. If you get your timing late enough you can make the manifolds glow.
Thanks for sharing your hard earned knowledge here!
Back in the 1980s, I had late 1960s cars that were subject to California Smog Laws. Living in Sacramento, I had to disconnect the vacuum advance line and cap the ports. Timing had to be set to a certain setting. Last was a sticker had to be placed under the hood somewhere visible.
Love the show. Keep em coming
Happy holidays Uncle Luke hope you have a great Christmas thank you for all your wisdom and knowledge I hope many more videos to come
Long story short get rid of that old school junk and get and get electronic ignition problem solved but Luke you're very knowledgeable on the old school stuff I have to give you credit for that I'm from the old days and I know old school stuff but the new electronic is for Superior then the old junk
Um.... electronic ignition still uses mechanical advance and vacuum advance mechanisms. Now digital advance like a progression ignition distributor is a different deal.
I have a chevy small block engine with small cam. Got it set to 800 rpm at idle. Advanced settings to 35 at tdc and 12 degrees idle at tdc. I used pressure vacuum gauge and the best reading I could get is 14. I was hoping to get it up to 16.Truck runs alot better than when I bought it. Im learning everything about cars from watching your videos and has hoping for suggestions.
Outstanding explanation.
Hi Luke, I’ve been watching most of your videos on ignition timing and learned a lot. Right now I’m restoring an old EFI Mercedes sl with my dad and I was wondering: how do I know if ignition timing is too much? The workshop manual 15 degrees before tdc at 3000 but that way the car is sluggish. With 35 degrees at 3000 rpm the engine feels like it has way more torque but can I get more timing or will I damage something?
15 degrees was very low. I think you are more in the right numbers with 35. Your EFI have a knock censor that pull of the timing if it gets to high I guess? Most naturally aspirated engines like a total timing of 32 to 36 degrees BTDC. What is right for your engine depends on the compression ratio and the shape of the combustion chamber. And of course your type of fuel. 10 to 16 degrees initial timing, and 18 to 22 mechanical advance is normal. And finally vacuum advance. My small block chevy 383 (6.3 L) carb engine with fast burn chambers, 10.8 compression, runs on 14 initial, 20 mechanical (max at 3000rpm) and 16 vacuum. Cruising at 3000 rpm it pulls a total of 50 degrees with A/F readings around 14.5. 15 l / 100 km or 15 Miles per gallon (USA). A rather radical camshaft for street use thou. Close to 500 hp.😃
Clearly book is wrong, 15 is a gutless thirsty slug. 35 sounds around right. . Searching between 32-38 degrees total should find the max power.
@@olekdah thanks for the explanation. I think the manual means 15 degrees of initial advance because this way the total advance is around 34-36 degrees at 3200 rpm (plus the vacuum advance). I made the rookie mistake of setting 15 degrees of total ignition timing and that’s why the performance were extremely poor. Btw I don’t think the car has any system to decrease the amount of timing in since it has points and the efi is very old (‘72 Bosch d-jetronic)
Hey Luke, been watching you for awhile now and have a question for you Sir.. I’m amazed in that I’ve been working on a Chevy C10 with a 383 Small Block. Initially guy I’d bought it from had vacuum advance disconnected. I re-enabled it. Ran better afterwards and better when re-timed. Then I had slight spark knock, and here is the strange thing which happened.. “Before getting the timing correct, I lessened the exhaust back pressure by going to larger diameter exhaust pipe, then here is the thing… The spark knock which was in engine went away with less back pressure in exhaust. This showing dynamics you had mentioned here?
Proof of your statements given I’d say, very cool Sir!
Question : and for example here..
“Less exhaust back pressure eliminated this particular engine detonation or “knock?”
Cool😊
Makes complete sense. I understand the whole difference between ported/manifold vacuum debate and how they work but when using ported vacuum we dont get any benefit from vacuum advance during idle. Would love to hear your thoughts on Unity Motorsports Garage theory on using adjustable vac advance can with manifold vacuum
I believe I have the highest viewed video on ported vs manifold on the Internet.
Perhaps this video will help to further explain the benefits: th-cam.com/video/bUv5tUC6Ioo/w-d-xo.html
If you follow along with that video, it’s extremely elementary.
Just remember who the engineer is and who isn’t out there.
100 percent correct thank you timing is everything!!!!!!!!!!!
Hey Luke, love your videos, very informative!
I have a question, why do most (if not all) jet boats have no vacuum advance? I do understand that it's because the majority of them will be ran at WOT most of the time and you're not really looking at fuel efficiency. Is there any other reason?
My second question is, since there is no vacuum advance, why do a lot of people run jet boats with maxed out mechanical advance even at idle?
I'm talking about 70s and 80s big block jet boats btw
Thank you.
Most of them are maintained rpm well above an advance curve range (above 2800rpm) and they are usually fairly loaded (so no vacuum for a vacuum advance, and no reason to have low load advance).
Couple that with the issue of the potential for moister to get into the distributor and rust up and seize the advance mechanisms, I completely understand why they don’t.
@@ThunderHead289 appreciate it thanks!!
What's up from Indiana 👋
Can you do a video step by step for the grandma's out here who are teaching themselves? Basically, someone like me who is absolutely clueless, step for step.
I CANNOT find an old school mechanic near me to adjust my Holley 670 truck avenger to my 454. Out of desperation I'm asking. (P.S. I enjoy your videos. Descriptions are fantastic)
I have a feeling that the VW Bosch 009 distributor without vacuum advance available in it's design was the reason for this episode.
In my '36 Ford lately, the vacuum advance has been making a screeching sound when the engine is running. When I disconnect the vacuum advance line, it stops making the noise. So I was going to pull the spring and piston out of the vacuum advance and try to run it by idling up the carb to counteract the having no vacuum advance stuff on it, but was also going to check and make sure nothing was bound up in the advance plate. The distributor was rebuilt before, but I'm thinking about sending it back to the rebuilder to go through it again if I can't find the source of the problem.
Take a look at one of those distributors when you get the chance, it looks like a divers helmet, and has 2 distributor caps. That's what I'm trying to work with.
Sounds like it might just have a ruptured advance diaphragm and that’s what you hear whistling as air is drawn through it. Easy test is to just suck on the hose - if it’s good, you shouldn’t be able to pull air through
Thanks for the great info brother
Have a very merry Christmas and a happy new year
Just saying
Vacuum works instantaneously, giving fast advance, working together with the acceleration pump squirts (carb side). As one throttles up to WOT, the vacuum advance goes max quickly and then decreases and eventually going zero (close to WOT). This is the basic idea. Centrifugal will only advance according to rpm, not helping out on the initial transient surge to start revving. This is the basic idea to have both working in tandem in the distributor. Great channel with really original stuff. Greets from Brazil.
i have an 8 1/2 to 1 77 buick i run with slightly advanced timing to get the most pep out of it. now i know why this works.
Thunderhead289 I would like to hear your thoughts on the FE rocker arm oil restrictors. Should we use them or not? I know the FE engines have oiling problem because of the oil being pumped out of the oil pan to fast to the rocker arms. That was a major problem with the 390GT engine back in the day. I did a test with a drill on the oil pump shaft and I could pump the pan down below the screen in about 30 seconds on a 428 SCJ engine. I bought this engine as a rebuilt engine. Ended up rebuilding it again with boring it .30 over. I got stung on that buy. Lol.
Hey Uncle Luke, I love your videos, any chance you have some more t-shirts for sale? I would love to wear one while working here on the farm : )
Happy holidays uncle Luke
Vacuum advance should be hooked to ported vacuum. Ported vacuum comes into play at light throttle/cruising speeds. This advances the timing, to advance timing even higher than centrifugal advanced timing. The purpose of this is for fuel economy. If you notice that mallory distributors do not have a vacuum advance, because they are not worried about fuel economy, just total advance at wot. When you are at light throttle, the throttle plates are open enough to allow vacuum to pass through the ported vacuum port and advance the timing. If you hook it to manifold vacuum, your timing will be too high at idle. This can cause rough idle. Hooked up properly, you should be able to get 4-5 mpg better than disconnected.
All things I have said in the past. I’m a huge promoter of ported advance. search ported vs manifold vacuum and see what your top search result is.
I even show that ported in fact does drop out just like manifold at hard throttle by having a vacuum gauge hooked to both.
For whatever reason folks tend to confuse venturi vacuum with ported.
I always try to explain that venturi vacuum is present in the carb, it’s what actuates the vacuum secondaries.
Hi there, could you please clarify why having more advance timing ( timing too high?) at idle with a Vacuum advance is a bad thing? I have been told that throttle response would be optimized with less mechanical advance ( but faster curve) in the distributor, and a higher initial timing ( say 10 -16 degrees BTDC) for Total Timing of 30-36 degrees. Cheers
Song by: Allison Jaymes with Play'n Staley and Jerry Can't-tell
The vacuüm advance was broken on my 1975 land rover.
And it noticeably decreased part throtle performance and fuel economy.
I fitted a fancy bleutooth programable distributor and drives a lot better now.
Its a very low perfermance engine so if its missing power its very noticeable.
It wouldn’t happen to be a progression unit by chance would it?
@@ThunderHead289 its a 123 ignition unit. Its the same sort of distributor but the progression unit might be slightly fancier.
It runs a 1000 times beter than a €40 Chinese point distributor.
Thanks for al the tips on carbs and ignition over the years!
Never used any of it on an American car though lol.
Excellent Content Thanks. Question? I'm struggling with understanding what "Initial Timing" Value is ideal for a given engine. (10°, 12°, 14° etc.). Would Hooking up a vacuum gauge to Manifold port and (adjusting the distributor at idle, transfer slots set correctly) achieving the initial timing by reaching (Max Vacuum, back off a tad) be a wise way to discover what initial Timing value is ideal for an engine? Thanks.
Thanks Luke
What is a carburetor?
I put a Blueprint brand 383 in my fathers car and their tech said do not hook up vacuum advance. He said at high rpm's their engine breathes so much that even with the throttle plates wide open it will still have manifold vacuum and advance the total timing to much. He said with a total mechanical advance at 3500 and 32 degrees before top dead center hooking up the vacuum advance could add several more degrees and detonate.
Not really possible unless you had a tiny carb - like a 500cfm, and then you would need to make at least 8imHg which is highly unlikely
@@ThunderHead289 The way they dyno them is unhooked. He said in most cases your way of thinking is correct, yet in this combination he said it will pull a measurable vacuum at high rpm's with the 750 cfm carb that was provided. I have no proof.
@@1958johndeere620 is just test it out personally - have a vacuum gauge in the cab and see what happens. On a 600dp I was close to that at 6000rpm on a 302 - saw vacuum gauge raise to about 1inHG.
I’d be surprised if a 383 could manage that.
If your happy with it, don’t change it - they just build in a safety margin for themselves, but it would improve economy.
You also can’t arbitrarily say x timing for x engine. A 383 in a light camaro would sport a totally different timing curve than a truck if both tuned for peak performance
@@ThunderHead289 He actually wants me to do the same thing when I get a chance. He wants to know if in our application what it does draw. It will take a co pilot to read the gauge, gets pretty busy.
@@1958johndeere620 yeah I agree - much safer that way especially at all the rpm
Yes....an engine with a static CR of 9:1 with a lopey high overlap cam loses cylinder pressure down low.....it'll need more initial timing to make up for lost pressure. With no vacuum advance, you'll only have initial + mechanical advance to maybe 35/36 degrees at lower rpms. (under 3000)
Add vacuum advance for more timing and efficiency at lower rpm.
On a small block Mopar, I have 35 degrees initial + mechanical all in @ 2,300 rpm in a heavy truck and it pulls well. No vacuum advance currently....it stopped working suddenly. Fuel mileage is terrible without it!
Luke....do you have Canada geese where you live? Or was that your chair? lol
That chair is super squeaky - the only reason I have cuts in this video is because I managed to rotate like 0.5 of a degree which emits quite the scream from that thing.
One too many gas station burritos I guess, too heavy for that poor little guy 😂
@@ThunderHead289 LMAO
If there was no reason to ever not run a vauum advance then why do all of the various distributor manufacturers build mechanical advance only distributors? I run the MSD pro billet version and it has no vacuum advance. My set up is far from a stock engine that somebody wants to pokey around with though. Maybe you should have said to keep your vacuum advance if you have built a stock to mildly modified engine vehicle that you drive mostly on the street.