The Vacuum Advance Debate!
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- เผยแพร่เมื่อ 16 มิ.ย. 2020
- Some say manifold vacuum...some say ported. As far as we're concerned, there's only one right way to power your distributors vacuum advance. Here's a quick demonstration that shows why.
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This is the first time I’ve ever seen this explained well
with out taking an hour, straight to the point...Thanks
Man, this is why you're a genius instructor! Who else would think to take a real distributor in the car to show what's happening?
Love the sounds of an old Dodge...the door latching, the hood groaning...I can almost smell the OEM musty smell..👍😂
Maybe that wasn't the car? Need to consult with Al's wife Peggy on this one. ;)
@@thisisyourcaptainspeaking2259 savage...😂
Not my old Mopar's..Mopars were always tighter and rattle free than GM/Ford..unless you only owned 400,000 beaters that were slapped with new paint!
@@wheels-n-tires1846
An old timer once told me:
If it smells like fish make it a dish.
If it smells like cologne leave it alone.
@@MrTheHillfolk haha. Love it. Always avoided the gals with too much cologne.. What they trying to hide...
I have not run across an engine yet that performs better with ported vacuum than manifold vacuum. Ported was an emissions era crutch from the early 70s. All the 60s engines used manifold vacuum.
my 1987 Honda CRX came from the factory as manifold vacuum. Had many people tell me to change it to ported instead of manifold. Pretty much ran the same at cruise, but at idle it was terrible, and would start overheating because of how hot the headers were getting on ported vacuum (about 5 or so degrees of timing (no vac, no mech) ), manifold vac would put it at around 20 degrees of timing (vac timing, no mech) and idles incredibly smooth
@@cmdr_scotty yep. My engine cooled down and ran super quiet when i switched to manifold.
Ford used ported in the 60's so......
@@yeboscrebo4451 same with my 350!
Exactly.
Switching to manifold vacuum cured almost all my problems. New rebuilt 350 stock except for an RV cam. New holley 600. new MSD distributor the list goes on and on.. Never could get it to idle correctly no matter what I did. 14 degrees btdc. Finally read that article, switched to manifold vacuum and its like a new car. It runs and drives so much better its unbelievable.
Yeah, uncle tony is wrong on this one. Listen to the actual automotive engineers describe the purpose of manifold vacuum advance. Tony has it backwards
@@yeboscrebo4451 link?
@@theungoliant9410 I’m sorry I don’t have one. You’ll have to run a search on the subject. I’m sure it won’t take long to find - it didn’t for me when I dug into the subject. There were two engineers in particular who have written extensively on the subject. If I remember correctly, one of them was a former GM engineer. Very interesting information
Same thing ... I switched to manifold and it's suddenly running so much better, it's unbelievable. Idles perfect, and you you tap the throttle, it just wants to go. For 40 years I've always done manifold from American Chevy 350s, Ford 289s, most European cars. Today many advice ported so I've been having a go at that. Nope. just doesn't work for a normal daily driver car with traffic choked roads in my hot tropical country.
@@theungoliant9410 th-cam.com/video/Y69OGBb0GGw/w-d-xo.html
I read an article by one of the engineers involved with designing these systems, he knows what he is talking about and says you always want to use full manifold vacuum. It keeps your engine cooler at idle due to the added advance, and has other benefits as well. Ported was something that was used later on to attempt to help emissions.
No. Lots of timing at idle creates heat.
correct. At idle, It will run smoother, cooler, create higher vacuum and run leaner increasing mileage.
Tony couldnt you find a busier😅 street to film on?
You, sir....... are correct.
this guy is the best classic engine teacher on the internet. I've learned so much here
Did you go through this issue with your corolla? I'm having issues with my ke55 atm. when advancer plugged into port. the car dies under accelleration. when unplugged completely and port blocked... car runs fine.. lost..
Uncle Tony's Garage: Great video Tony. Retired licence mechanic here. I used two vacuum gauges, one on manifold and other on ported to teach apprentices the difference of the two. Very useful when adjusting the spring pressure and max vacuum advance. Cheers.
it’s all the same except at idle and WOT (wot has no vacuum anyways so it’s a moot point). Manifold has higher timing advance at idle, lower EGT’s and not as good emissions, then pulls timing as the throttle blades are opened. Ported vacuum has no advance at idle, because it sees no vacuum at idle. As the throttle blades are opened, the vacuum rises and it adds timing advance. The way that you determine which is best is the way your distributor curve is set up, and your application. Some guys will swear by ported only, others by manifold only. If you have the ability to use a dyno I’m sure there’s a negligible difference in part throttle power, because in the middle of the part throttle operation, with the manifold vacuum advance dropping and the ported rising, they intersect at the same amount of advance. So, to sum it up, they achieve the same effect, just one adding timing and one taking timing out. The engine will run differently on each due to the way they add or remove timing. Remember, this is only idle and vacuum cruising, wide open throttle doesn’t matter for vacuum advance.
6 of one half a dozen of the other.Your description is pretty spot on i think.
I remember having a '71 ford fe that had a coolant temp vacuum switch that when coolant temp got to a determined level it would route manifold vacuum to the dist. in order to increase timing and raise idle speed.That car detonated like mad on any kind of a part throttle load and started my education of vacuum advance. I remember trying so hard to keep the vacuum advance and tune out the detonation cause why I don't know.... because i was giving up maybe a mpg in fuel economy i guess LoL
I love how you make the explanations so very simple by just physically showing it actually doing what it does.
Vacuum Advance plays a huge part in Fuel mileage... I have found on my tunnel ram setup I get better driveability from Manifold vacuum.. you can use adjustable vacuum pots so you can dial in your vacuum advance and have your cake and eat it too....
2-3 MPG and a Fan Clutch on the street almost the same. Big difference on MPG added up.
I just made the switch to manifold on my 72 f350. Of course I had to make plenty of adjustments with timing but it was far superior to ported. The first thing I noticed was how quiet it was on a cold start. The engine ran much better and my mpgs went up by 3. I just don’t get why you’d want to run ported
One thing Tony doesn’t mention is, retarding timing under throttle can prevent detonation which can be a good thing in a performance engine. I run manifold vacuum and got a smoother idle and it stopped pinging at WOT.
I get that too, far superior performance and driveability on manifold vacuum. This debate will continue on, at the end to each his own. I'm happy always with manifold vacuum.
I thought the only difference between full vac and ported was having extra advance at idle. Ported timing waits until throttle is just off idle to work. So it makes no difference either way. The power and fuel economy is the same. The only change from the exta timing at idle is smoother idle, cooler temp, better vacuum assist to power brakes, ect. depending on your engine combo, it may run better at idle. The higher vacuum signal lets you lower the throttle plates even more to gain better results from your idle mixture screws. Remember, we always set our base timing and and check max timing with the vacuum advance disconnected anyway. WOT doesn't use vacuum advance, so there should never be a change in performance. Anyone who disagrees must be setting their base timing with vacuum advance connected. This is wrong and will affect many things negatively. Love your videos, Tony!
Well said Ed. Full manifold vacuum is the best way. I think ported started with the Clean Air Act in 68.
Ported vacuum is pretty low just off idle and manifold vacuum is pretty high just off idle. You’re getting much more advance with manifold in that situation. It’s not just idle where the difference is. In fact, most vacuum canisters I’ve come across don’t start advancing timing until about 5 hg. So if your canister is connected to ported and you’re in light cruise with those throttle blades barely cracked, you’d be getting zero advance. If you were connected to manifold you’d be getting all of it - like you should.
Absolutely correct. The biggest problem is that the off-the-shelf distributors have too much mechanical advance for ported vacuum. I had DUI build me a distributor with 12 degrees mechanical advance and a 14 degree vacuum canister. I start with 24 degrees initial timing which using ported vacuum is your idle timing. But I vary that from about 22-26 degrees as needed. So this gives me 24 degrees at idle, 36 degrees total timing and 50 degrees light load cruise which is exactly what a first generation SBC wants. My engines all run perfect.
For Ported Vacuum
Idle 24
> 12 mechanical advance
Total 36
> 14 vacuum advance
Cruise 50
DUI recommends manifold in their literature. How many of those 14 degrees ported vacuum advance are you getting at high speed/low load cruise? At low load, manifold vacuum is high and ported is quite low obviously. Run two gauges at once to validate. Seems like you could be getting more mpgs out of your cruise with more timing, manifold timing.
Great work as always Tony, clear and concise answers and demonstrations that clear the air and give actual information that is physical and tangible for everyone to see and more easily understand the concept. Nicely done sir
I guess I'm a younger guy, mid 30's. Grew up in the age of distributorless ignition and electronic fuel injection. But the more I watch these videos, the greater respect I have for the engineers of the past for all the clever ways they thought of ways to improve performance, economy, and drivability on an....analog level{?}. The things they did before modern computer power are really quite impressive.
IMO, vacuum advance was originally hooked up to manifold vacuum. Later, the manufacturers hooked it up to ported vacuum for emissions purposes. The big downside of ported vacuum is the engine tends to overheat on hot days in traffic. Ported vacuum will cause the engine to idle with less advance than what it wants. Idle loves advance. It runs cooler and more efficient.
From what i've heard, never seen one myself, In the late 60's, in California, they started to install a second vacuum advance that was activated by a temp sensor. I think this was an attempt at fixing the overheating problem. So, when the engine started to overheat it would add additional advance from the second canister and cool the engine. Could be wrong. Just a theory.
Ah, yup. I think you nailed it. That explains the purpose of those (pvc looking coolant switches) perfectly. I do believe, you are spot on. All that foolishness should be bypassed and we should take our vac right from the intake in the first place.
It’ll only overheat if the manufacturer didn’t design enough static advance in, or the idle jets pushing the whole lean burn thing way too far.
I had a 75 Ford Granada with 302 that had that system smog pump , EGR valve and vacuum hoses everywhere if you took one or two off and did not know where they went your in trouble for sure . It has several water temp sensors with vacuum hoses hooked to it when it got to the set temp it would open and send more vacuum to advance the distributor more timing kinda of a neat idea .
Love it!! First you held class, then when heads started shaking, you took everyone into the lab. "A video is worth a thousand words"...😁
This is basic stuff, dont know how there is debate on it, but you had a great way of clearing the air on the subject Uncle!!👍👍
The demonstration was hardly relevant
@@yeboscrebo4451 Hows that??? For people who are unfamiliar with vacuum advance, don't understand it, or might be 'visual leaeners', its totally relevant. How could it not be???
@@wheels-n-tires1846 because the distributor is only part of the symbiosis and doesn’t operate on its own so showing what happens in a disconnected distributor is hardly a comprehensive teaching aid. People think that you can just switch between ported and manifold and “see which one works best”. Wrong. If you switch between one or the other, the initial timing may need resetting, the mechanical timing curve needs resetting, the vacuum advance canister needs to be adjustable and set correctly and finally, even the carburetor may also need adjustment to achieve results. Uncle tony failed to explain WHY time is needed as certain inches of vacuum or certain rpms, he just pointed to a dizzy and said “look, see”. Sorry, even knowledgeable dudes like uncle Tony have crusty ideas they’ve harbored for years that are just wrong.
@@yeboscrebo4451 Lots to unpack there...so first, in other videos hes talked about timing and carb relationships. This vid wasnt about that. It could really be condensed into "see, using this port, good. Using that port, its working backwards, thats bad." Or.... "this shows exactly what happens when you hook it to the wrong hose"...
Its meant at a 4th grade level for folks who know little or nothing about distributors, advance systems, carburetors, etc... And Tony certainly wasnt saying you could switch back and forth between ported and unported to run your vacuum advance distributor. Thats idiotic, and nobody that has a clue thinks that. Not sure where you got the idea that anyone thinks that!!! That might be the silliest statement Ive heard on YT in a long time...so its pretty bad!!
So anyway, while youre right about the finicky relationships of timing and carburetion, this vid didnt intend to address that. Why does he have to address everything in each video?? Maybe try watching others. Id imagine theres HOURS of Tony on here explaining timing, curves, carburetion, etc. So if you expected it to give a thesis-level dissertation on that relationship and it's details, well guess youll just hafta stay dissappointed, because this vid, and frankly the whole channel seems to be more about basic info and explanations for beginners, or people who only have experience with newer cars and systems. Your conclusion that the old timer is dumping old and incorrect theory on here is whats wrong. I read and used Tonys knowledge for years and years...decades before he ever had a TH-cam, and can say that I put together a half dozen street/strip Mopars with that knowledge, and they were better and faster because of it.
@@wheels-n-tires1846 wow that’s a lot of words to not actually refute any part of my comment. Did you ever “unpack” the subject matter of the comment i made? Not sure where I got the idea? Have you read the comment section? Lol. As I already explained, the demonstration was not relevant precisely because it was overly simplistic. To explain the difference between ported and manifold vacuum, it’s not good enough to have a dizzy, removed from the engine, and expect to illustrate the relatively complex interactions between all three forms of advance timing. You can’t just say “look the advance mechanism is moving here on manifold and here on ported” because each case requires changes to the other two forms of timing advance. Just the fact that he did not acknowledge this interaction is indicative of his misunderstanding of the benefits of manifold vacuum advance. It seems like uncle Tony just gotten stuck on the teenage hot rodder “more timing equals faster” approach without every revisiting this idea in his old age. Your better off reading what the actual engineers had to say about it than an old hot rodder stuck in his ways.
When I was a kid, my mother was being shown a vacuum gauge. She then sucked on it and seemed very proud. I had no idea why....
WTF? LOL
Baaark
@@AustinRBa could be they ignited an advancement
Tell your mom i want my gauge back dammit...........
I may know your mom
Hey Tony, I've been dealing with old British cars that not only have vacuum advance but also vacuum retard using a double diaphram distributor. I plug both of them and do what I call a "road tuning". I set it up with the light in the shop and then drive and get the best responsive advance I can on the road, reset idle and call it a day. It's worked for years.
My new MSD distributor instruction book said to connect the vacuum advance to the ported vacuum of the carburetor, not manifold vacuum. So, this is what I did, and it works just fine. 😊
Also there are thermal switches that when the coolant temperature reaches 225 deg F the distributor vacuum advance is switched from ported vacuum to manifold vacuum to increase the timing for lower engine temperatures at idle. This was common back before electronic engine controls. These switches can still be found for sale.
Or you can do the same thing with a 12 volt three way solenoid valve and a switch. So if you get stuck in traffic in your hot rod you can just flip a switch to help prevent over heating on hot days.
Great video! I agree, ported, only, ever! I had a great Vocational Auto instructor. We had a Sun distributor machine. He taught me how to use it and to set up and recurve distributors. Must have done 100 over the years. I loved using that and a Sun engine scope, he also trained me on. Fun stuff. A lost art these days.
Thank you for all the great info and breaking everything down step by step, and for free to everyone who wants to learn the right way and understand how and why for every video you make. Thank you
Tony you are giving me flashbacks, its the mid 1960's auto shop at Martin VanBuren HS Queens. The vacuum gauge was our #1 go to diagnostic tool. Electronic test equipment was years away. I remember buying my first dwell meter and thinking how advanced things had gotten.
Great demonstration. You do a great job of explaining stuff in a way anyone can understand. Good teacher.
professor Tony's classroom! You really do love teaching!
Sweet demo rig. I've never thought to try that. Really interesting to see a real world experiment. cheers Unc. My spare sbf points dizzy recently got rigged with a battery, coil and a plug, held to the workbench in the shed by a chunk of railroad track and spun up with a skateboard wheel with a silicone hose tyre mounted in the drill. Mission was to calibrate the new old been in bits custom tach. Works a treat. Dead nuts on to the digi timing light tach after tweaking it. Some people would have rigged up a signal generator circuit but analogue with dangerous fizzing taser sparks way more fun. Even the wife was impressed.
Uncle Tony, Thanks for tuning me up! It’s been a while since I’ve been in this deep. I’m doing a major rebuild on my ‘79 F100 (bought it new at age 19). Since most emissions parts are obsolete I’ve had to reimagine as best I can. OE vacuum diagrams showed the vacuum advance working off manifold vac, trying to set timing, adjust idle; and it wasn’t making any sense. I think I’ve got it now.
I owe you one, or more.
Class is in session, pay attention.Thanks UTG. Stay safe, God Bless
Thanks Uncle Tony! There are still a few us gearheads around that remember switching to ported vacuum after "desmogging" a 70s GM product. Power timing with a buddy!
Desmogging meant switching back to manifold vacuum
Well, we know the canister works. The distributor has to be curved to work on whichever port you use. If you take a stock distributor that was curved to run on ported and you put it on manifold you will have way too much timing. Likewise, if you plug a distributor into ported that was set up for manifold you won’t have enough. So there is truth in both camps on which is “better”. Best to know what you have for mechanical advance in your distributor and how many degrees at what vacuum your canister delivers to determine what will work for you. Excellent real world practical demonstration from Tony. You won’t get that anywhere else! 👍
For stock type stuff ported is great, cars form the factory did it that way for a reason.... I had a car with a bigger cam and found it worked best hooked to manifold. The reason why is to get it to idle in gear, I needed the throttle blades open too far causing the idle mixture screws to have no effect. So, hooked to maniflod I got some extra timing that raised the idle allowing me to close the throttle and allowed idle mixture adjustment. This would not have worked if I did not have an adjustable vacuum can the stock cans have too much advance. In full disclosure the stall convertor was too tight for the cam, when I put it into drive the car learched pretty bad. So, yes when modifying engines the combo is very important.
This issue is always a debate, IMO the most important thing is to understand timing and the advance mechanisms. Then use a vacuum gage and timing light to actually know how much timing your engine is actually seeing under different conditions. Too many will want to argue about this and they never drove a car around with a vacuum gage or checked their mechanical advance curve.
Keep up the good work Tony!! Dont worry about the know it alls, they are just fine. Your are giving a great education to the younger/newer guys!! Its weird to think that there are a lot of 50 year old professional mechanics who never worked with carbs and distributors.
You can also drill a small hole in the front throttle plates, this will allow you to bring the idle screw down to cover the slots in the base plate. If you go any higher on cam profile. Another trick to let a little more air in was to adjust the screw on the secondary shaft to open it letting more air through and accomplishes the same thing. Either will let you drop the Idle screw down to function.
I’ve been always using ported vacuum. I’ve had to listen to so many people telling me to run manifold vacuum, but I read something long ago about which port to use, and I’ve stuck with it! The only thing that I’ve done is try to limit the amount of advance, and keep my initial timing up. It’s worked so far, so good! 😉
first time ive seen a demonstration like this.... even though I already knew how it worked it was awesome to actually see it in the real word with an engine and real vacuum... fascinating stuff tony!!!! great video!!!
Again, late to this video viewing.
Lovin you classroom venue. Was a little worried, bout you being along side the highway with the kind of drivers out there these days.
Appreciate the effort, and you managed to show this very “thick headed” guy how this system works.
Thank you sir.
Hello Uncle Tony,
Thank you very much for all the information you have given us. 1st Oct, 2019 I bought a 65 Mustang that needed everything so I could learn about these things we drive every day. TH-cam and manuals have taught me much but there are things that slip through the cracks here and there that I have to catch as aside note in some video about something completely unrelated.
Then I found your channel. Your so direct and actually bother to put into video format your advice and knowledge. I understand how actually bothering to set up, film, edit, and post is a time-consuming process. So again, I thank you for taking the time to put your experience into TH-cam so green mechanics like myself can learn.
I have a small request and if a video has already been made then please if anyone could point me in the right direction I would be most gracious. You had spoken briefly about how your lifestyle is in your cars. Specifically, you don't keep cars with really high-end paint jobs because of the upkeep a super high close finish requires. I have been trying to discern what you do to paint your cars by looking at your cars in your videos. What do you recommend as a paint job for a daily driver classic?
So far I have done all the prep work, then primer, blocked it, then base coat, and blocked, then matte clear with hardener. What would be the simpler way for daily driver upkeep?
Thank you again for everything.
I wish there were some sort of marks to be able to see it move. Maybe it’s by old eyes not being able to see anything move
Me either.
Definitely not just you! I had to zoom and stare and rewind a little.... finally saw it. Phew!
We are not alone
You got balls standing on the side of the road like that lol
I thought I was the only person crazy enough to tune the engine on the roadside....lol
Brian J. Medina your math is lacking skills
Meh. Been doing that for years
@@Welcometofacsistube holding a sign? Lol
@Curtis Fleabag I'll only do that with a homeless and hungry sign in my hand. Not a distributor lol
In other words, light load and substantial vacuum implies a less dense charge in the cylinder, and the flame front is moving slower, so the vacuum advance bumps it up so the flame front hits the piston at TDC, which gives more power for that part throttle setting, which in turn enables you to let your foot off the gas even further for better gas mileage.
Yes, that’s what manifold vacuum advance gives you, not ported
I thought I understood port vs manifold for distributors, but this made is so clear I won't ever forget
My car seems to idle better with the extra timing from manifold advance. It comes off when I hit the gas. So what? It goes back to where I set it in the first place. What am I missing here
You are not missing a thing, Tony is.
Nice job, great real world practical demonstration. Thanks for posting this.
Nice demo Tony!!! I too had questions and that makes it pretty clear.
Great job focusing on the fundamentals and great demo
Something that helped me as a kid was to think of it as "negative pressure" instead of vacuum, then sea level pressure after opening the throttle.
Holy shit, what a great demo! I’m glad you didn’t throw the dizzy like it was just a carb
This channel is a gold mine. I learn something every video. I always thought vacuum advance's were always connected to manifold until the early 70's when they switched it to ported because it allowed for better emissions. My understanding was that if I want better emissions I should do ported, but if I want better drive-ability I should do manifold.
Yes ported it runs hotter so it will burn off the fuel more although in stop and go traffic in the summer you can get into trouble running ported . I ran ported and I could get 14.7 or more on the AFR gauge idling on manifold I would stumble out past 12.9 or so less timing the leaner it is more timing the richer it is problem is the distributor is not tuned for manifold vacuum a adjustable pod is a must .
On my old Porsches I always ran mechanical advance but on my Thunderbirds I always stay manifold.
on a stock distributor....you are not wrong, sir. really appreciate the demonstration and posted content! explained very well, and clearly.
Perfect explanation with a demonstration to help us visual learners!
1960s car were always ported vacuum to the distributor. Late 70s 80s cars use manifold vacuum with the thermo switch between vacuum port and distributor. I believe some use both to the thermo vacuum tree and delay valves/check valves as this was to delay vacuum advance untell engine was at operating temperature and converter was hot for better emissions.Less timing equals more complete combustion and less oxides of nitrogen. I did state Emissions testing, tuning,rebuilding the computer control carburetors. Adjusing with old Catalytic converters on the vehicle or a cylinder with low compression in one cylinder this was challenging stuff at the time.
Hi uncle tony, very good video I’am learning how to set up a engine your way . I’m self taught working on cars for along time I don’t know everything I wish I did at 71 years old just keeping at it I like working on cars thank you for all your help 👍🚘🔧
This is very good. The vacuum system is overlooked by many and understand by a few people. Remember, your knowledge is not the same that other people have or think they know.. People start off wrong and the stay wrong. It takes some person like you ( Has credibility) to head people in the right direction. Thanks again
As I recall, vacuum advance is always useful when you have high vacuum because you also have stratified lean conditions. Could be at idle, could be descending a hill, could be light throttle freeway cruise. That vacuum advance is there to help light the very starved almost closed throttle poor mixture, light it early so the weak flame front has time to progress to peak burn.
If you watch your own video here as you just presented it, you see that when you accelerated, you were on mechanical advance only, both times. Once because vacuum advance fell back to mechanical only, and once because you ported it. Same result.
The vacuum advance can't "remove" mechanical advance. They are separate systems ...
Exactly. "When you need it most-" it was *never there* in the ported scenario- how can it be "taken away?!"
From what I can tell, you are correct. Notice around 4:58 as UT releases pedal, i.e. cruise condition (minimal fuel, somewhat high rpm) the vacuum advance can be seen to go away. But actually, you want mechanical and vacuum all working at that condition as the low cylinder filling and small amount of fuel need max ignition timing. So taking away vacuum advance at the condition, takes away much needed advance.
The timing gets taken out during accelaration because cylinder filling increases so a faster ignite happens as a result of the richer mixture.
From all the reading plus some testing I've done, I think the issue is that when hooked to manifold going from ported, idle timing goes up too high, so the distributor gets pulled back to end up at the same 12-14° idle timing when it was on ported, but now the vacuum is adding some of that idle timing. But that then limits the higher rpm timing because the mechanical is now down from 12-14, to probably 4 or so (rough numbers for illustration). So when acceleration is applied and vacuum drops, the mechanical is lower than it was when ported as the distributor was pulled back to compensate for the extra that manifold gave it at idle.
So if we go back and set timing with vacuum port plugged off, and set say 12° purely mechanical, then plug in manifold vacuum and timing goes up to say 25 (rough number)... Instead of pulling back the distributor, leave it, instead, lean out the idle mixture screws and turn out the idle speed screw. By lowering rpm in this way, it should reduce some of the mechanical advance. Or so goes the theory that David Vizzard puts forth.
Effectively, idle timing can be fine on ported but at cruise you want manifold advance to get that high timing number. That's the theory anyway
I think 🤔 the ported was a emissions thing i tried both on my 390 ford and on ported it ran good and the AFR was easy to get 14:1 especially on the Fwy only it woukd get hot 🔥 in stop and go idling traffic in the summer the exaust was 50 percent louder and at startup i would have water vapor coming out of the exaust . On manifold it was alot richer and i would need jet down a size or so alot harder to get perfect AFR usually be around 13:20 ish idling and 13:80 or so on the fwy but if was 50 percent quieter exaust and did not get really hot in traffic .
Alot of people say the factory never used full manifold ?. I think before 1975 they did on the valve cover it has a low initial timing like 6-8 degrees if it was ported it would or should say 14-16 degress ...
@@TheThirdWheel618 All of my older vehicles used full manifold vacuum advance except a 1973 Dodge Dart with a slant 6. Once I bypassed the OSAC valve and gave the vacuum advance can full manifold vacuum, the engine ran cooler and more efficient. Better MPG's, better drivability, better cold starts.
@@muziklvr7776
Yeah i think before 75 for sure it was all full manifold Ford had a valve that operated by engine temp you were on ported untill the engine reached a certain temp say 200 then it would shut the valve off and it would go to full manifold to cool the engine down ???? That says it all the factory knows they can reach better AFR with ported at idle but it creates a lean condition so they came up with the valve idea .
That’s the best example of how it works I’ve seen! Thanks for the video I’ve been hooking it up wrong for years now!
Thanks Tony Best explanation. I am a visual type of leaner not reading a book or explaining the function and not showing how this function actually works while in use.
Sorry Tom, I couldn't see ANYTHING moving in the distributor at all. As a side note, I love your channel & your old school style & have learned a great many things from you in the past. Thank you Tom. Len from Canada.
Thanks for showing that..I notice the importance of that specifically when using a 34 pict 3 carb and svda distributor on an aircooled vw engine..with the vacuum advance drivability is better
I think its something that will be debated endlessly. The only way around it is to dyno two cars, one with a factory engine and the other with performance mods. Test both running both ported and manifold and see the power band differences. Love your videos. All the best from Oz
Or just take the same engine and tune for ported on the dyno then tune for manifold and see which one wins.
There would be zero difference on a Dyno. You don't leisurely cruise on a Dyno, you crack it wide open under a heavy load--- ported or direct manifold vacuum are BOTH going to give exactly zero added degrees vacuum advance, no partial throttle runs on a Dyno.
Glad I drive a truck and don't drive a dyno
@@hiswordheals9710 From what I've read, most modern vacuum advances will give you 12 to 14 advance and mechanical advances will give you 12 to 14. As the vacuum drops, the mechanical advance makes up for it depending on both timing curves. Some mechanical advance only distributors will go as high as 28 to 3,000 rpm or even higher, but mechanical advances are more typical of motors built for heavy load applications such as tall deck 366's or tall deck 427's (extra oil ring in the pistons to handle higher advance/compression/heat at higher RPM's under heavy load).
Some vacuum advances are also adjustable so we can play with the timing curve. We know that as RPM's increase, the vacuum increases even as your primary throttle plates open up but as your primary plates open up more than half way, the vacuum begins to drop.
I'm spitballing here, but I think the vacuum begins to drop as the primary throttle plates open up past half way but if your engine RPM's are in the high 2000's or higher the vacuum is still mostly maintained so it doesn't drop by much.
It's when the secondary 4 barrels (throttle plates) open up that the vacuum tends to crater. Your vacuum advance drops to zero on a SBC with your carb fully open up to around 4500 but then slowly picks up past 4500 advancing minimally by 4 degrees or so around 6500 RPM's. But then, if you are pushing a motor to these RPM's on a dyno, it's built for it. This isn't to say vacuum advances won't be used on the street pushing these revs, but the chances are more likely that a motor on a dyno pushing 6500 or higher is built to race with a lock out distributor with all of it's advance at startup.
The type and size of your carb also effects vacuums. A Rochester for example, has much larger secondary venturi and throttle bores than primaries so as your secondaries open up on a Rochester, the ported and manifold vacuums drop lower and more quickly than equal sized throttle bores. Same holds true for larger CFM carbs such as a 750 on a 350 sbc, the vacuum off your port will be lower on a 750 compared to say a 600 CFM carb because your venturi and throttle bores are larger on a 750.
Hi performance cams, ported heads and high rise intakes will also drop your vacuum (substantially), but that's for another conversation. 🙂
I thought I understood everything about vacuum advance. I never took a distributor in the cabin with me though. Once again UTG blows my mind. 🤯
Uncle tony I love your videos. Hi from Australia. I feel if people are not up to speed with basic things like vacuum advance, Mabey they should choose a new hobby. But then I remembered we all have to start somewhere. So. For the young blokes who watched this I thank you. You will teach them
I remember the old Autolite dual point distributors on hi performance Chrysler products did not have a vacuum advance.
Thanks Tony.
Excellent explanation. Most people overcomplicate these things because they don't understand fully what they are talking about. The simplicity of this demo speaks for itself
The demo is TOO simple. He showed what happens to the dizzy when the advance canister is hooked up to ported or manifold. He didn’t adequately explain why you need different timing at different levels of load or rpm. For a more comprehensive demonstration, the dizzy needs to not be removed from its symbiosis with the other parts of the engine. A better approach would be to show two different vacuum gauges one from ported and one from manifold at the same time. Then, take the engine through different circumstances in load and rpm to show what is happening with the timing. Uncle tony was able to explain the opposite of the truth because his demo was overly simplistic.
Awesome visual display of how it works. 👍👍
Great demo, I think you did a good job explaining the differences.
Why not let the weights do the advancing and keep the manifold vacuum advance for the best idle and light throttle cruising?
Off idle response and cooler running engine have nothing to do with performance? Don’t think so. There is a lot going on with a mechanical distributor, springs and weights, mechanical advance degrees, vacuum advance degrees, response adjustable and non adjustable vacuum cans. Most people don’t have the time or energy to dial in and tune a mechanical distributor let another understand how it all works together. It’s hard to explain, I have tried every which way with my olds 350 and 350 sbc, hands down manifold for me.
68 440 magnum. Original Carter 4429 only had one port available (other than the choke pulloff) and that was for ported vac advance.
There will be spring or weight differences on a stock distributor, depending on whether they want to emphasize street performance, track performance, economy, or emissions. You can alter those goals by changing total vacuum (different can or link), and/or by changing the centrifugal springs or limiting the travel of the weights (more difficult).
Just remember if you limit vacuum advance or weight travel, you may need to alter idle timing to ensure higher rpm advance while cruising is not way off.
You might also find a deceleration solenoid (or vacuum device) that prevents the throttle from slamming shut and sending manifold vac to over 25, causing timing to advance when it would drive emissions highest (you're not interested in performance when decelerating anyway but Uncle Sam is particularly interested in emissions at that moment). Salute that solenoid, it's a good soldier.
But when you are part-throttle accelerating your 70's Dodge and interested in performance for a few seconds, there's a traitor called the OSAC Valve (usually hanging off the air cleaner body) interrupting the vacuum hose from the carb to the distributor. That thing prevents vacuum advance for several seconds while accelerating, and since you just left the stop sign, your revs are not high enough to give centrifugal advance, so with timing delayed you end up pushing the pedal way down to keep up with the 60's car beside you (no OSAC delay). Sound familiar? Bypass that OSAC, plumb the vacuum direct to the distributor.
Thanks Tony. Well explained and demonstrated.
I've was taught to do my timing with the vacuum advanced off and then attach the line to the port on the base of the carburetor, never thought that much of which side to have the distributor to get its vacuum from, I've always put the line to the carburetor ports, if on the manifold vacuum tree then cap it and place it to the carburetor.
Best way I've ever seen someone explain it with a visual
Well there's that AHA! Moment I was looking for, thanks alot man.
I always learn something when I watch Uncle Tony. Hard learned knowledge that he's willing to share. Thank you for taking the time to teach and entertain.
If you didn't already know this, then you are not a hot rodder!!!
This confuses me. Wouldn’t you want timing advance at high vacuum/low throttle situations? There is almost no port vacuum when the throttle is at or near idle.
Yep. Tony’s wrong
ABSOLUTELY!!! Anyone that doesn’t understand this doesn’t understand ICE’s!
Thank You Tony! This Came Right On Time!!!
That’s a good demonstration thanks uncle T
Tony give those hood hinges a little wd40 🤣🤣
again, great explination! thanks Tony!
Of course now I'm contemplating hooking up some kind of valve to both ported and manifold vacuum with some sort of cable or solenoid to switch between the two. :)
@Jonny longfella Cause it'd be possible? :)
I'm a huge fan of manifold vacuum and I can see many benefits on my 41 Chevy inline 6, since I swapped it over to manifold. Especially mileage and temperature. What a lot of folks saying : ported came with emission in the 60s is a myth though - my 41 had ported from the factory, some cars even earlier - why? I don't know, since the engineers back than must had have something in mind - but that would be an other interesting discussion.
In my personal experience, I m never able to get full advance at low speeds with ported vacuum. Throttle angle is too low to uncover the port.
The difference is absolutely not opposite. The only difference is you have no vac advance at idle. Off of idle it is the same. The question is what do you want at idle. And the answer is not the same and every condition.
Sorry. Ported vacuum is for smoggers. At idle and low throttle the mixture is lean and needs advance. Smog distributer curves had tons of advance, like 12*, at idle to compensate somewhat for the ported vacuum advance. They did this to make the car run hotter. My 68 L36 Corvette used 4* initial and full manifold vacuum to the cannister.
Correct. The ported vac would be exactly the same as manifold vac anytime off idle. So manifold vac would allow more advance at idle and for longer burn times needed at idle. Plus low base timing for ease of start before building vac
Well done unc! This subject is getting deep on vacuum subject.
I'm confused. You demonstrated what happens when you get ON the throttle on manifold, but then demonstrated when you get OFF the throttle on ported. what does ported do when you get ON the throttle that makes it better?
You explain everything so well but there's always someone who wants to disagree with what you have to say, which is from many years of experience. Most of them probably never even turned a wrench!
Thank you Professor Tony! 😎
Is this backward for just me or a bunch of people? I thought manifold vac was better for big cam engines to help smooth out idle. To date everything I have read has always said manifold vac advance is the way and that ported was only good for some mopars and later used as a crutch for the gas crunch smog era emissions. Great video as always demo is excellent. Maybe I need to go flip some hoses around and save some at the pump due to more mpg. Thanks for the knowledge!!
It really takes a really knowledgeable and has some common sense mechanic to dumb this stuff down to this level. I admire your patience with the keyboard warriors.
No it takes a really dumbass to complicate it in their head more than it really is! If you need it dumbed down to grasp it!!
I learned something ...again , I’m going to have to watch the other video now to find out what ported vacuum is now
THANK YOU , i COULD NOT EXPLAIN THIS ENOUGH TO PEOPLE AROUND HERE!
Thank you sir, you conveyed what i needed to know masterfully
Man wish I had know this some 30 years ago. Completely understand the difference between ported and manifold vacuum. Now that explains why it never ran as good as it should have.
Had to pay attention really hard, but man I get it! Thanks Uncle Tony!
Thanks for sharing your knowledge old man 😎
I've been watching your videos and f* me... I've been doing wrong for years now! And you teached me lots of distribuitors, I can't even thank you enough Uncle Tony! Much love from brazil! Keep it up!!!
So doing a lot of reading on this subject. With leaner mixtures you want more advance for a full burn. And as the mixture richness increases you want the timing retarded since the higher cylinder pressure doesn't require as much time to burn as a lean mixture. So wouldn't that mean the most efficient burn is happening with manifold as ported is making for a less efficient burn and higher exhaust temps? Which is putting more stress on the motor with more heat?
Demonstration was awesome, easy to understand now
The ONLY difference between the two is you don't get vacuum advance at idle with ported vacuum. They both work exactly the same at part throttle and wide-open throttle. Use which ever one makes your engine run best.
It will let you know.
Works for me!!!
Nope. Watch a manifold and ported vacuum gauge side by side and you’ll see that they are not the same at, for example, low load/cruise conditions where the throttle is barely cracked and manifold vacuum is high. When you’re flying down the highway in cruise you need the timing only given to you by manifold vacuum advance. Better mileage and cooler temps.
@@yeboscrebo4451 Once that throttle is opened past idle, there is FULL vacuum.
I love these types of videos ,short,sweet and to the point and great explanation!
How is the bodywork coming along?
An hei or gm distributor would have been a bit easier to actually see what's happening there but you sir are 100%spot on