Ported vs Manifold Vacuum: How I am Going to Settle the Debate!
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- เผยแพร่เมื่อ 12 ก.ค. 2023
- Ported vacuum or manifold vacuum advance? Which is better? Many automotive TH-camrs believe it is the former, but I disagree!
@newguysgarage6802 @UncleTonysGarage @ThunderHead289 @UnityMotorSportsGarage
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My 72 f350 quieted waaaaaay down, ran much cooler and I significantly increased my mpgs after optimizing for manifold vacuum.
I respect addressing the engineer part. Aside from the fact that I have been an engineer in the automotive feild before, I say that as a way to differentiate myself since frankly anyone can make a video saying whatever they want.
Engineers typically (definitely not always) have some level of cause/effect and reflective analysis hardwired into their way of thinking.
I also got here the hard way, im not a degreed engineer - ive had to teach myself and beat out the on paper engineers to get where im at.
I trust youll test both manifold and ported advance and follow through in a way that you optimize your high load mechanical timing with both.
Go through all the scenarios, idle, cruising, high load (both rolling into it and from a stop) and report your findings honestly - thats all anyone can do.
As i said in my last comment, utilizing ported advance isnt about just the vacuum advance - its about what it allows you to do with mechanical timing.
If my engineer comment seemed aggressive, i dont really love my likness being used to harvest views in a thumbnail. Kind of an unwritten youtuber rule 🙂
That makes sense. Engineers generally have analytical minds and are good at troubleshooting complex issues.
Also, sorry about the thumbnails. Figured it was appropriate since I mention you in the videos. If you'd like, I'll edit them and remove you from them.
@@thejunkyardnecromanceryour fine, be cool to meet up sometime - shoot the bull, laugh about trusting our lives to garbage ancient cars. Wouldn't have to be strangers then and stuff like that would be less surprising 👌
@ThunderHead289 that would be cool!
I’ve learned a ton from your channel thunderhead. I just don’t see why you’re not on the same page with this one.
@@ThunderHead289
@thejunkyardnecromancer You guys send me the address, and, I'll send the beer.
TIMING AND VACUUM ADVANCE 101 by GM Engineer.
The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.
The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.
At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).
When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.
The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.
Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.
If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.
What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.
Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.
For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively.
WOW. Thanks for you insight
Good vid. As for commenting on TH89's " engineer" references seemed unnecessary as I believe it was not overly emphasized but rather simple evidence that he is no dummy. The guts of both of your channels discussions are key and I have learned from you both, thanks!
1) Neither side is 100% correct:
Almost every 70s era vehicle I have worked on has a vacuum switch on the thermostat. This switch will use the ported nipple when cold and the manifold nipple when hot. So, the dist "sees" ported cold and manifold hot. That is because factory engineers knew ported vacuum overheated motors and switching to manifold vacuum afterwards did not overheat. LOOK AT THE VACUUM DIAGRAMS they will lead everyone to the correct conclusion.
I totally agree, manifold vacuum. But! Not even an honorable mention of John Hinckley or Lars Grimsrud? Too Corvette specific?
www.corvette-restoration.com/wp-content/uploads/technical_papers/Timing101.pdf
This and transmission kickdown explain the success we had with our pos regularly trouncing "max build" and high-spend fancy-dancy cars.
This should be interesting! I'll be waitin'.
Thanks!
Great video, brother. We all need to be able to talk and figure this stuff out.
For sure!
When I was young, the emissions were the "toe-stubber" for me...
The Professional Toejam 😁
I am definitely going to be watching. I want to really get into tuning my fastback for power and maybe some cooler temperatures. I just mostly drive it for pleasure but the motor can pit out some power and heat. I get decent fuel mileage even though it really isn't tuned for anything other than WOT. It starts harder when it is warm/hot.
With a vacuum advance you might make better power and get better fuel economy! I'll find out!
I've seen a couple videos on adding a fuel pressure regulator or a return style fuel pump/filter to help reduce vapor lock, also adding a phenolic spacer to help prevent heat soak in the carb from the manifold. Also try adding shims to the hood hinges to allow heat to exit from the cowl area.
You have my sign. Love your opposition standing. And my engine the manifold.
Fantastic discussion and video series on this topic. If you may add "stumbling issue off idle" to the list; as I believe this is the crux of the issue most people have when first attempting to run on full manifold vacuum. When the switch is made; it is very likely that the operator will be able to tune the carb idle circuit a little leaner and turn the idle adjustment screw down to lower the idle speed as the engine will be running more efficiently with the vac advance pulling additional timing in at no load idle speed static conditions. This is ideal while you are idling and the engine is operating cooler via an optimal lean conditions carb idle circuit. But it sets up a quandary and IMO, is the key issue in this debate: In dynamic transition off idle; when the throttle is stabbed and the butterflies open, the motor stumbles because its transitioning from this very lean idle, no-load state to high load open throttle. The accelerator pump circuit is designed to fill this transition with a shot of fuel to burn until venturi air velocity begins pulling fuel from the main circuit. Failure to tune the accelerator pump shot to maintain proper air-fuel ratio during this transition off-idle is why I believe most revert back to ported vac. Tune the accelerator pump nozzle size to to eliminate the stumble; typically you will need a larger nozzle to get a quicker shot. Thompson Performance sells a PowerBlast fuel atomizing plate which shears the pump shot fuel stream and approximates fuel injection level atomization of the pump shot fuel during this off idle transition, offering even finer control of the pump shot.
If you don't tune the pump shot for this off idle transition, you will interpret the rich idle circuit - ported vac condition as "smoother"... and as a result; your engine will run hotter and burn more fuel at idle and in cruise mode. Calibrating each subsystem to operate at peak efficiency in both lean and rich modes results in EFI fuel injection like response, and the snappy throttle response desired.
That's a good one! I'll add it to the list!
Intake vac. Worked best on my 69 351w. Run rough on ported vac.
Please include what information you gather as far as setup differences. After your last video i just swapped the hose (ok, i did more than that but certainly ad hock) and drove it a few days on manifold, ive long had two gauges showing both and am aware how they relate to one another. Interesting discussion
2) look at a EFI timing table. Its based on load(pressure or vacuum) and most EFI timing tables use manifold vacuum/pressure (load) to dictate timing. I personally have never seen a timing table that has idle timing set at 6 or 8 degrees. Its always 12 to 18 degrees unless you are dealing with altitude and have to set it at 20 to 24 degrees. Any tuner will tell you that a large spike in timing (IE not smooth) is detrimental to the engine's performance. Do ported vacuum dist. have a spike from idle to acceleration? yes.......when cold, maybe not when hot due to temp switch.
Nice response, looking forward to the follow up! And I would agree that you need a lab coat, however I think a robe would be more appropriate for a necromancer.
Thanks! And a robe might be more necromancer like haha
I agree, manifold is the way to go. the only problem with it is the abrupt drop in timing off idle and on acceleration causing stumble and hesitation, been fighting that problem for a long time. i just recently came up with a simple idea and solve all those issues. i install a small adjustable restrictor valve in the vacuum line to slow down the vacuum drop rate to the distributor therefore giving the mechanical advance time to catch up. No more stumble, No more hesitation and response is so snappy.
I also installed a vacuum gauge on the distributor side in the cockpit to monitor vacuum drop rate.
Let me know your thoughts...
Very interesting idea! Never heard of something like that before!
Like a JB weld inside a union with a pinhole in it? Or plastic weld?
Same problem with a 358 sbc 488/488 with a toilet single plane victor intake and 2 inch riser with a Rochester quadrajet carb. It does what yours does whene switching to manifold. I tried 8* all the way up to 15* base. It likes 12 either way and it ran better off the light with ported. That’s in a 88 s10 single short with a th350, with 373 gear
Sounds interesting! Do you have a product to share?
@@fuelbasti I just used a fish tank bubbler metering valve in the vacuum line and adjust to suit.
@@lucsavoie9501 genius 🐠
It seem to be one of those subjects where you ask 10 mechanics and get 10 different answers.
Definitely seems that way haha
Your way to speak and represent the info got my subscribed. Love it and agree - put engineer at the end is strange move. I'm engineer but Electrical and even so I've no idea about even automotive electrical stuff! I can calculate and figure out but it is not my field of knowledge or expertise after studying and experience. They all cool guys but the CAN BE WRONG sometimes. It is normal. Good luck!
Thank you!
So it seems that it depends on your set up.
There are benefits to BOTH depending on what your running.
NOBODY can say for sure which is better !!!
The answer is IT DEPENDS .
How did the auto makers set it up? Intake vacuum
Up to a point they did, but at some point they all switched to ported vacuum and other more complicated setups.
Interesting test but I think some things are being ignored by everyone. 1) vacuum diagrams....notice how there are vacuum switches on the thermostat housings of some 70"s vehicles. Factory engineers knew ported vacuum caused overheating, so the vacuum switch on thermostat housing pulled manifold vacuum to distributor above a set temperature. Ported vacuum when cold, manifold vacuum when hot. So why do ported vacuum systems have you pull vacuum line off dist. to time vehicle? Well because engine should be warm to time and the dist sees manifold vacuum due to temp switch on thermostat maybe? Look at vacuum diagrams they help explain what each side is saying.....maybe both are right?
I came here to watch the update DDG said you would do on stone/rock soup Lancer. But after seeing nothing but manifold/port videos 5-9 months old i went back & checked when DDG posted the video of him getting Lancer running and its only been 6 hours. So ya its prolly still at his shop. But im curious about this new curfuffle i seem to have stumbled upon, sooo now im a new subscriber. 😂 i hope all you guys put your pride aside and work together. And in the immortal words of Rodney King: "Can't we all just get along"?
Welcome! Stone Soup hasn't made its way over here quite yet, but it will soon!
And I have a lot of respect for the guys mentioned in this video, but disagree with them on this topic haha.
Since one engine i have is running boost I have a locked distributor and a MSD 6AL box. I can program the curve I want. David Vizard recently did a video "cheapest Octane Booster" water Injection.
That sounds like a nice setup!
1964 Dodge Dart, 170 CID, bone stock. 60,000 miles, 120 lbs compression. 20" vacuum at idle . Runs buttery smooth. So, I run 16 BTDC, base timing. Vacuum advance pulls 18-20 degrees, Mechanical advance must be adding another 24 above 3,000 RPM's. So, somewhere between 55 and 60! LORD. Anyhow, Cold start... ON the fastest idle cam, the Ported vacuum must be kicking in, plus some mechanical... putting me at 30 BTDC, dead cold... but, runs like a top. Fast idle drops to lowest fast idle... then timing moves back to approx 20 ish. Off the cold start, fast idle.. Back to 16, and idles like a kitten. PURRRRRRR. So, I ran a Temporary Vacuum gauge on the dash, and tried it both ways. It might be my imagination... but, the throttle response seems better from 1000 to 2000 RPM's, on ported vacuum. Steady state vacuum ... (As seen on my Temporary, vacuum gauge) seems like its the same.
**My Theory** The accelerator pump on my rig.. might be a little bit weak. So, the ported vacuum is actually compensating slightly... by adding timing... at just the right time. The motor seems to want more timing... due to a slightly lean mix on quick throttle opening. The throttle response seems excellent on Ported vacuum. It is hard to tell... but, after swapping to Manifold... the motor seemed more sluggish.
16 BTDC is the highest vacuum reading at idle. If I use manifold vacuum... It pulls way too much advance at idle, so... I would need to move the base timing to probably 5 BTDC, and before i pull the distributor, to move it a tooth, ... I guess... I'll throw in the towel and not mess with it.
I'm looking forward to your next video! I may have incorrectly commented about my '47 Chevrolet on the previous video. I thought it had ported vacuum, because the single place for the advance to connect is about level with the throttle butterfly, and I believe it has a vertical slot into the carb throat. It's a Carter W-1, and has only the one vacuum connection, with a steel line going to the advance mechanism. Today, I connected a vacuum gage and timing light. I also removed the cover and counted the starter ring teeth in order to calculate the degrees of advance and retard. My engine has a hole in the flange facing the flywheel, and has a mark on the flywheel for TDC, a mark for 5 degrees BTDC, and a triangle that I don't yet know the purpose for - it is ahead of the 5 deg BTDC mark and not referenced in the manual. Per the manual, I set the timing at the 5 degree mark with the engine idling before shutting it off. By putting a meter on the points and knowing each flywheel tooth is 2.59 degrees, I found that without vacuum, the timing is 18 degrees ATDC. This vehicle can be hand-cranked, but it still seems 18 degrees is pretty late in the ball game for ignition timing. I get about -15" Hg at idle, which is enough to give full vacuum advance actuation. There is no measurable vacuum while cranking the engine - this comes after it starts - so it's possible part of the reason for vacuum advance is to allow cranking - no kicking back against the person or the starter. I connected a tee fitting and drove the car a bit - the vacuum goes as high as -5"Hg based on engine load, and goes a bit lower than - 15" when throttled back and coasting. I can "blip" the throttle, and the vacuum is less for a split second or so. On this car, the vacuum advance mechanism actually retards the timing until the engine is running, and also retards the timing when the load is so great (dense charge?) that the vacuum decreases. Interestingly, my ancient vacuum gage has a "normal" range marked, with the area at less vacuum being marked "late ignition timing". I retarded the timing, and the vacuum did decrease a bit - so timing apparently affects vacuum, as well as being controlled by it!
But not all vehicles use vacuum the same. I had a '77 Honda Civic back in the 80's, and it had vacuum connections on both sides of the advance diaphragm. The side of the diaphragm that connected to the linkage had a seal that allowed that side of the diaphragm to be used - so vacuum on one side retarded, and vacuum on the other side advanced. I never had the facilities or tools to understand how that system was supposed to work.
Very interesting! With the timing marks on the flywheel, do you have to be under the car to time it? And Ford had those dual action advance/retard vacuum canisters too! I'm also not sure how they were set up. Never owned a vehicle with one.
@@thejunkyardnecromancer There is a hole next to the starter with a pointer sticking thru from one side. Shining a timing light at the hole makes the marks on the flywheel line up with the pointer in the hole. Kinda hard to see, being behind the starter and having the distributor in the way. Unfortunately, the manual's illustrations are few and unclear - and there is a matching hole (no pointer), very easy to see, on the other side of the engine - but no flywheel markings line up with that one when cylinder 1 or 6 fire! Ask me how I know....... This must've been years before they started marking the harmonic balancer or pulley and having the stationary degreed plate next to it. If you think about it, the markings on the flywheel are further away from the crank axis, and yield better resolution. I think I'll mark my pulley and then bolt on a degreed plate next to it. One of my goals is to have a static timing mark, so I can get the timing very close before starting the engine. Here's a thought: since the timing is set with the vacuum present and timing advanced, we don't know if the timing is retarded too much when starting - we assume the vacuum advance moves the correct amount!
I have worked on small block Chevy’s for 40 years. I have tested both methods over the years and manifold vacuum is the way to go. Keep in mind neither ported or manifold work at WOT. Both are worthless. The main advantage with manifold vacuum is during idle especially with an aggressive cam. But you will also have better idle results with stock cams too. Ported vacuum was used due to emission standards and better fuel economy during cruise mode only. That is it. Ported doesn’t give you better performance or power. It actually makes the engine work harder at idle. So connect the distributor to the manifold vacuum and your engine will thank you.
Exactly!
Assuming we are not talking about a cam'd hot rod motor (?), I want you to think about being stuck in stop and go highway traffic like an afternoon commute ... Running an EGT probe and water temp gauge find out which way the engine will creep along smoothest and coolest ?
Oh, and this argument is like Ford vs Chevy (Pontiac obviously), and which oil is the best (0W-30 Euro Spec obviously) ... 🙃
Ok. I'll add that to the list!
And what you meant was Ford and 15w40 diesel oil. ;)
As manifold and ported vacuum act opposite when off idle where one drops and the other increases, I wonder what would happen if you tee them together with two check valves to get the best of both, now you can have way advanced timing at start up that won't kick the starter, and idle timing jumps up and stays up when you first open the throttle, just a thought.
This would be an interesting experiment except that ported and manifold vacuum are exactly the same when the throttle is open. Teeing them together would just give you manifold vacuum. Ported vacuum is the vacuum signal above the throttle blades and manifold vacuum is the signal below the throttle blades.
Just run it however you like,
It all depends what applications vehicles be used in,
That’s why you get opinions all across the graph.
Type of fuel being burned, location of where you live ,
My opinion , which doesn’t matter, I don’t run any vacuum to my dizzy,
I looked up the timing specs for my 1967 Newport 440 4bbl automatic transmission.
Base timing - 12.5 degrees, Mechanical advance - 0 degrees@ 325 to 475 rpm, 0 to 4 degrees @ 475 rpm, 4.5 to 6.5 degres @ 640 rpm, 8.5 - 10.5 degrees @ 2200 rpm.
Vacuum Advance - 0 degrees @ 8" to 10", 5 degrees to 8 degrees @ 13", 9 degrees to 12 degrees @ 16" ported vacuum from the factory. The only emission control on the the engine is a PCV valve. It is rated as having 10.1: 1 compression and 375 hp. Just a note that not all pre emision cars had manifold vac to the distributor from the factory nor did they cruise with a 14.7 to 1 afr, more like 13.5 to one at a time when gasoline was 35 to 40 cents a gallon. Great times for power but not so much for the enviroment. Good luck with your testing, looking forward to the final results.
Thanks!
I had a Newport custom, factory air, factory power seats, vaccum gauge from factory, dual exhaust. It was sold to me as I had a 1968 fury and I was told the interior would be a bolt in. Every time I went to part it out I couldn't bring myself to do it. Eventually some dude I went to high school with knocked up and I sold it to him. Was also a 1968 I believe, never had anything that old with power seats and all the other bells and whistles
A dyno is a great tool when used correctly.
If WOT timing is 32* then changing ported vs manifold vacuum adv is not going to matter at all doing WOT pulls on a dyno.
if you're going to do steady state/rolling road tuning then yes, it would be great to graph the vacuum going to the adv at specific rpm/loads.
It would also be nice to chart the timing along with that.
As for tuning, the only changes that should be made are idle speed and idle mixture screws.
Base timing should not change because that affects wot timing.
The vacuum port would just add or do nothing to the timing at idle.
Exactly! I am testing all of this right now! Almost done with a follow up video with my findings!
Go watch the video by stereopolice. He conducts a great demonstration using two gauges while driving, One gauge to ported (timed) and one to manifold vacuum. He idles, cruises and accelerates to show the impact on the gauges. The clear winner is manifold vacuum. It appears the engineers back in the 60’s and 70’s before emissions actually knew what they were doing.
I'll check it out!
You could use a Dragy GPS to get mostly repeatable data on 0-60 times, etc.
That's not a bad idea!
The reality is it depends on the engine. If the engine likes manifold vacuum advance then use manifold vacuum, if it doesn't like it then ported vacuum advance might help the engine rev up faster due to manifold vacuum falling off when you punch the gas.
I'm going to test this! Stay tuned!
I dont think there is going to be a definitive answer to all. Each has its place. I like a KISS approach. Keep it simple stupid. In most NA applications your gonna want 16-24 deg at idle, 30-40 deg total with mechanical advance all in. I would say play around with it and do some 0-60mph or drag strip passes to get the best WOT performance. Adjust the intial and the total mechanical advance along with the advance curve. Maybe throw in some different mechanical advance springs and/or weights. Then play with an adjustable vaccum advance can. Play with it on manifold or ported vaccum and adjust the amount total vac adv. If using manifold vac, adjust initial to a combined idle timing of 16-24 deg. Check for off idle performance and initial adv to mech adv transition. Also cruising part throttle economy at different speeds
That's the plan! Working on all these things right now!
Interesting topic, had to subscribe so I can follow it along. It seems that a lot of the debate is rotating around the split second when blipping the throttle from idle, and for most scenarios this is rather useless. Engines are not producing a lot of power under 1500 rpm, after all.
Indeed! Thanks for the sub.
Yeah that blip right off idle is also where I do my highway cruising. It’s the stretch of real estate between a shut throttle valve and the ported vacuum hole in the carburetor. That little stretch is the territory of the manifold vacuum advance. I don’t see how the ported guys don’t get it
Light the fire when it needs to be lit.
The statement of ported being for emissions is wrong. Everything is a tool that can be used on different combinations. There’s not general rule here.
Might help to also run a afr gauge.
Not a bad idea! I'll see if I can get one.
I'm so confused 😢. I just wanted to drive and chill. Little 350 😊.I'm running Ported 😊 maybe you guys should race 🏁 😉 😏.
A race would be fun!
I think it is really funny that there is any reason other than emissions to run ported. Now maybe if your vacuum advance, or distributor is worn out. There may be failures. But from my experiences I noticed slight differences in the response to acceleration. And felt ported was more positive in acceleration than manifold vacuum. Like maybe a stumble or hesitation. Now maybe there can be corrections in advancing or retard. But I really think if your car is designed to run it. Would it be wrong to go against the design? Especially if it is an oem production design? If your running headers, cat deleting, , pump deleting, aftermarket suggested upgrades or etc.... It is still going to have a vacuum advance hooked up. 😉
Until you do your next video on the topic im still with Vizard
I purchased a progression ignition for my 440 after a preview on a thunderhead289 video. The instructions say Must connet to manifold vacuum. So thats what i would do. If i had run an MSD and they said run ported i would do that. My guess the company that made the dizzy would know more about it than i do. Not sure why Thunderhead289 would side with ported when i know at least 1 of his cars run a progression dizzy.
It's hooked to "manifold vacuum" because it's a map sensor that should have a signal all the time. You program the timing control parameters on progression 👍
You can avoid the inherent drawbacks of both manifold and ported with progression since both require compromises somewhere where progression is not bound by such limitations.
Indeed. This is a bit of a different setup and isn't really applicable to this debate. Sounds like a really cool engine/setup though!
@@thejunkyardnecromancer
I don't know, The dizzy still in the box 440s a fresh rebuild.
I have a duster 360, 600 Holley and Chrysler ignition. The dreaded Orange box. Owned the car six years had manifold vacuum. Switching to ported maybe 2 years ago. Apart from adjusting idle and advanced timing maybe 30 degree total. I cannot recall. I've always tuned for highest vacuum Never really made any noticeable difference.
I bought an expensive DUI distributor for my 300 i6. The instructions also told me to hook up to manifold
Do you still run the same base ignition timing as per spec?
In most cases I'm not. I like to find what the engine looks for timing and tune my distributor to fit that. I create a timing curve based on when the engine starts to ping throughout it's rev range, and after I've found the sweet spot at each 500 rpm interval, it's gives me my base timing.
I don't think I'm explaining it very well, but I'm working on a video that shows the process.
This debate ..where are the engineers to help us
I would love to hear from some automotive engineers!
no vacuum at all... vw with 009 dizzy
3) Why do carburetors have nipples for both ported and manifold vacuum? If all the dist needed was manifold vacuum, there is absolutely no reason for a ported port. Ported vacuum is to allow a motor to start easier maybe, then switch to manifold vacuum once fully warm. Maybe emissions I do not know for sure. I do know factory carbs had both ports and there was/and is a reason for that. So, both ported and manifold vacuum are required and have to be used correctly. I thing both arguments are right and both are lacking in the finer details.......vacuum diagrams.
Old carburetors never had ported ports.
Explain, ignition timing!
REBEL Crawdad
Still testing this ? I'd like to see the results.
I am! Almost done actually!
all the information is usefull agree or not thank u very much
Thanks!
How about this, put a T fitting in the vacuum hose and use both, when manifold vacuum drops off ported vacuum takes over and keeps the timing up, that's how I have it on my 73 Challenger 440, back in the late 70's early 80's Toyota ran 2 vacuum lines to their distributor so I just T'd mine to both vacuum sources.
But ported and manifold are the same once you open the throttle. So, honestly it sounds like you just created a small vacuum leak.
@@thejunkyardnecromancer People are saying that manifold vacuum drops off witch cause your timing to drop off momentariley witch it does happen a split second or so that's what the beef is about that split second drop off, the addition of port vacuum on the same hose negates that, Toyota has been doing that years their vacuum pod has 2 ports and has 2 seperate vacuum hoses, it does the same thing.
Where is your lab coat?
It's one of the things I need to purchase for the follow up! Haha. I need some black gloves and mirrored glasses as well so I look like a mad scientist! XD
@@thejunkyardnecromancer I just sent you an email
My car runs twice better on manifold bbc!!
MSD, Holley and most other manufacturers state clearly that Ported/time vacuum is the proper way to hook up your motor when you have non-race cams where the idle vacuum is higher, and, when your idle and low cruise vacuum is low due to bigger cams; then and only then should you run manifold vacuum because it can help "OVERCOME LOW VACUUM IDLE AND OFF IDLE DRIVING" Watch Andy and David's video 100% without cherry picking it like you did.
IT ALL BOILS DWN TO HOW HOPPED UP YOUR ENGINE IS.. THIS AND THIS ONLY IS WHAT PREDICTS PORTED VS MANIFOLD VACUUM and the idiots just can't figure this out but act like mentally challenged argumentors.
I watched both part one and part two of Andy's video. Nowhere did with he, or David say this that I can remember. Can you give me time stamps where they said these things?
In all my mopar manuals 67 68 and 69 the vaccumtube is above the blades. Both 2port and 4 ports.
Guess they had no clue.
I explain why this is in my first video on the subject. You should check it out! Also, I'm going to be putting this all to the test in my follow up.
Vizard said the emissions stuff and switch to ported started happening late sixties
Please include what information you gather as far as setup differences. After your last video i just swapped the hose (ok, i did more than that but certainly ad hock) and drove it a few days on manifold, ive long had two gauges showing both and am aware how they relate to one another. Interesting discussion
Will do!