Moparts

Is Vaccum Advance Really Such a Bad Idea

Posted By: fatman

Is Vaccum Advance Really Such a Bad Idea - 02/14/21 12:41 AM

Hey Folks, I drive it 120 miles round trip to the track, timing locked at 30 degrees. Many engine builders are wary of it, but Ive read (Richard Ehrenberg) that not having it washes down the rings, and I suspect it's why my exhaust stinks so much while driving and after. I don't yet know who manufactures one that will clear an Indy Legend head, but I'd like to know what experience is out there. (fuel injection isnt in the budget right now, multiple projects lol)
Thanks, scott
Posted By: fourgearsavoy

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 12:58 AM

I went a few rounds with Eberg on this topic at Carlisle years ago and we kind of agreed that for a pure stock engine sure it's a good idea. But for most engines with modifications like a cam and moderate compression you need to just customize a simple distributor with mechanical advance will do the job.
Gus beer
Posted By: Stanton

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 01:24 AM

Well you must have just worn Eberg out to have him concede on this topic because unless I'm mistaken, he's always touted the benefits vacuum advance would have on NASCAR and other race engines.
Posted By: 68 HEMI GTS

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 02:03 AM

I run vacuum advance on my 10sec street car. Works well, gets great mileage, and the plugs always look great. Just requires the distributor to be set up correctly and you need a adjustable vacuum advance to limit the total.

Attached picture 1833BA56-2903-4A76-91F8-D376F4A39246.jpeg
Posted By: calrobb2000

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 02:04 AM

hi
why would you not use vac adv on a steet car ?

you are just wastin gas on any cruse time .

only people that i know that dont use it dont undestand it
Posted By: Hemi_Joel

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 02:53 AM

Every street engine will benefit from properly set up vacuum advance using non-ported manifold vacuum. Smoother, cleaner idle, better mileage, cooler running, longer life. You can plug it for racing. Drag race only engines should not have it.
I'm not saying nobody gets their car to run good on the street without vacuum advance, but you can make it run better and more efficiently at part throttle with it. Most of the time on the street is part throttle.
Posted By: Diplomat360

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 02:58 AM

Originally Posted by calrobb2000
hi
why would you not use vac adv on a steet car ?

you are just wastin gas on any cruse time .


Have to completely agree with that statement...no reason NOT to use a vac advance, it has a number of benefits and literally is one of those freebies that we can take advantage of.
Posted By: Hemi_Joel

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 03:40 AM

At part throttle, the air/fuel mixture in the combustion chamber is very sparse, so it burns much slower than the piston travels away from it. For efficient use of the fuel to make power, the maximum flame spread and cylinder pressure needs to occur near the beginning of the downward movement of the piston on the power stroke when it has the most mechanical advantage and before the exhaust valve starts to open. With the slow burning part throttle charge, it needs a bigger head start to be maxed out in the sweet spot. Vacuum advance gives it the head start it needs, so the piston is not past 90 degrees atdc when the flame front is at its peak. Ever try to pedal hard on a bike when the pedal is past 90 degrees? And the exhaust valve on a performance mill will start opening +/- 70 degrees before bottom dead center. Lack of advance will send part of that still expanding charge out the exhaust.
Posted By: Cab_Burge

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 04:07 AM

I've tried several different pump gas street motors both ways and really didn't see a performance gain with using the vacuum advance confused shruggy
I don't track the MPG either or drive them more than 50 miles in a single day usually shruggy
I do work on my carbs and distributors to get the mechanical advance and AFR the way I want them also up
I like to see between 14 to 18 BTDC at idle on the timing and between 34 and 36 degrees BTDC above 2000 RPM, 12.8 to 13.5 AFR at WOT and between 14.2 to 15.3 AFR at light part throttle cruise with the heat range spark plug that motor wants to stay clean at idle and at WOT wrench up grin
Posted By: sr4440

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 04:37 AM

Originally Posted by Hemi_Joel
At part throttle, the air/fuel mixture in the combustion chamber is very sparse, so it burns much slower than the piston travels away from it. For efficient use of the fuel to make power, the maximum flame spread and cylinder pressure needs to occur near the beginning of the downward movement of the piston on the power stroke when it has the most mechanical advantage and before the exhaust valve starts to open. With the slow burning part throttle charge, it needs a bigger head start to be maxed out in the sweet spot. Vacuum advance gives it the head start it needs, so the piston is not past 90 degrees atdc when the flame front is at its peak. Ever try to pedal hard on a bike when the pedal is past 90 degrees? And the exhaust valve on a performance mill will start opening +/- 70 degrees before bottom dead center. Lack of advance will send part of that still expanding charge out the exhaust.


hemi Joe has this correct, when setting up a street/strip engine always run some form of advance. On the dyno, with a part/ light throttle engine load, as soon as you start adding advance you will see the BSFC number start dropping like a rock. (BSFC measures how efficient the engine is. A lower number is more efficient)

How much to add, that is going to be trial and error. I wouldn't worry about "washing" out your rings or cylinder walls, you are under light load and the fuel is still being burned, just going out the exhaust.

Joe
Posted By: fastmark

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 11:34 AM

Originally Posted by Hemi_Joel
Every street engine will benefit from properly set up vacuum advance using non-ported manifold vacuum. Smoother, cleaner idle, better mileage, cooler running, longer life. You can plug it for racing. Drag race only engines should not have it.
I'm not saying nobody gets their car to run good on the street without vacuum advance, but you can make it run better and more efficiently at part throttle with it. Most of the time on the street is part throttle.


I am working on a 440 six pack with with the Promax metering block. It does not have the fitting in the metering block for the normal vacuum line for the distributor. Now that port on a stock metering block is ported, correct? Meaning it does not get vacuum at idle but at throttle, correct? So, I should run the vacuum line straight to manifold vacuum, right. I read on one of the Corvette forums and they were saying the first Tri powers had the vacuum advance straight to the manifold vacuum.
Posted By: fatman

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 01:07 PM

Thanks Everybody, I appreciate all the input. Now I have to find one that will fit, at least it's safe to call Indy these days lol
Posted By: mopar dave

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 01:19 PM

yes, manifold vacuum is what you want. I have seen it both ways, but my opinion is off manifold would be best.
Posted By: lewtot184

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 01:22 PM

the problem with a vacuum advance on a performance street/strip car is that people don't understand them and don't know how to tune one. typically it seems to be human nature to dislike what they don't understand. i use vacuum advances on both my cars and would never take them off; unless i was using the car in some sort of competition where the advance wouldn't work anyway. i made learning to tune for a vacuum advance a priority.
Posted By: madscientist

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 03:02 PM

Absolutely, positively for damn sure you NEED vacuum advance.

You also need to run a curve. Not sure why you only have 30 total, because that seems really low. Plus if you have ANY sort of ignition box, the timing WILL retard with RPM, so you actually will have LESS than 30 total with the distributor locked out and RPM retard.

So get a curve in it and add vacuum advance.

When you run the timing that far retarded you get a TON of heat way too late in the power stroke. On blow down, when the exhaust valve opens you still have combustion happening and all that heat goes into the exhaust valves, the exhaust port and out the exhaust.

That’s not only a power killer it’s a parts killer. So yeah, you are wasting fuel and power and I’d bet everything I have, everything you have and a bunch of stuff neither of us have that your exhaust gas temperatures are through the roof.

I used to see it all the time when I was tuning at the track and guys were logging EGT’s. The EGT would be where they thought it should be, or some other hero told them the EGT was too high, so they start adding fuel (usually wrong) and pulling timing (usually wrong) and the EGT would keep on climbing.

Then when you tell them they are doing it backwards, all the guys who’ve never looked at a data log ever tell them why they need to go to a colder plug ([censored]??????) and get the timing down some more.

Get some timing in it. And get a curve. And vacuum advance.
Posted By: madscientist

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 03:04 PM

Originally Posted by 68 HEMI GTS
I run vacuum advance on my 10sec street car. Works well, gets great mileage, and the plugs always look great. Just requires the distributor to be set up correctly and you need a adjustable vacuum advance to limit the total.





If there was a like button I’d hit that thing like a lab rat hitting the button for more meth until it killed me!!!!
Posted By: furious70

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 03:18 PM

To NOT need or benefit from vac advance, someone would need to be able to explain what they did to the engine to no longer require it, if we all agree that the OEM application of it is correct and useful.

Possible things people might say are modern shape combustion chambers, quench pistons, computerized engine controls....essentially trying to tell Hemi_Joel that the control he explained that is needed because of inefficiencies in the engine are combated in some new way.

I'm not saying that at all, just laying out the argument someone would need to make because what he said is still true with a big cam and more compression...
Posted By: DaveRS23

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 03:23 PM

Adding, let alone tuning vacuum advance is just about the same as choosing and tuning a carb for most guys. It is just over their head.

For a car that cruises at light load, steady throttle why wouldn't you want vacuum advance? What could possibly be the down side? I agree that on some combos the advantages could be modest but there would still be advantages. It would seem that the biggest hurdle to widespread use of vacuum advance would be the misunderstanding of it's benefits and the lack of ability to tune it.

I use a hand held vacuum pump to test and tune my vacuum advance. You can hear the difference in the exhaust note as you add advance at cruise. I find that finding a good amount of advance is not difficult at all. The hardest part is making the necessary changes to the advance stop.

It would be nice if there were some more definitive data on this. Maybe an episode of Engine Masters?
Posted By: polyspheric

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 05:18 PM

For engines close to stock tune (any size, but mild cam) full vacuum to the distributor works well.
As the cam approaches 240 degrees @ .050", full vacuum works at idle, but as you open the throttle vacuum quickly dies, which reduces RPM, etc.
Ported fixes this, since idle is based solely on initial advance it's completely stable until a later throttle position.
You can even fab a new port position by inserting a small tube right through the casting to a point (generally slightly higher to delay vacuum) than the original, which will not add vacuum until slightly higher throttle disc angle. Hint: doesn't need to be horizontal.
Try both, keep the one that works best, cap the other (don't blank it), it may help the next time you change your tune-up.
Posted By: Moparite

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 05:29 PM

Quote
I am working on a 440 six pack with with the Promax metering block. It does not have the fitting in the metering block for the normal vacuum line for the distributor. Now that port on a stock metering block is ported, correct? Meaning it does not get vacuum at idle but at throttle, correct? So, I should run the vacuum line straight to manifold vacuum, right.


Yes to the first question and a big NO to the second! The distributor vac advance needs ported NOT manifold vacuum. Manifold vac is high when the throttle blades are closed giving max advance until you open them up then it drops to nothing. This is backwards of the way it's supposed to work. Ported vac is higher during open throttle and nothing when it's closed. I can't comment on what GM did but this is the way Chrysler works. And to make it short the advantage in a street motor is it will apply vac advance before the rpm's get high enough to apply the mechanical advance. For a strip motor it doesn't make sense because as soon as the light turns it's full throttle and the rpms are up where the mechanical advance kicks in.
Posted By: jbc426

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 05:39 PM

I ran my RB locked out at 35*, and the motor loved it. It never hard started hot or exhibited detonation. I too wanted to add vacuum advance, and came across a relatively new distributor from Progressive Ignition that had a fully adjustable digital vacuum advance feature in terms of total added and at what vacuum. The rest of the distributor's timing adjustment was digital as well.

I now have the start timing set at 21, idle and total timing set at 35* and at high manifold vacuum it goes up to 42* with the addition of the vacuum advance.

I bought one and installed it last year. There is a small learning curve as far as set-up and dialing in, but it was quick and easy to learn, as I can see where the timing is in real time while driving the car around. Yes, I too follow the Four Seconds Flat method of hooking the advance to manifold vacuum.

Here's the link:

https://progressionignition.com/shop/ols/categories/chrysler
Posted By: lewtot184

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 05:39 PM

Originally Posted by fastmark
Originally Posted by Hemi_Joel
Every street engine will benefit from properly set up vacuum advance using non-ported manifold vacuum. Smoother, cleaner idle, better mileage, cooler running, longer life. You can plug it for racing. Drag race only engines should not have it.
I'm not saying nobody gets their car to run good on the street without vacuum advance, but you can make it run better and more efficiently at part throttle with it. Most of the time on the street is part throttle.


I am working on a 440 six pack with with the Promax metering block. It does not have the fitting in the metering block for the normal vacuum line for the distributor. Now that port on a stock metering block is ported, correct? Meaning it does not get vacuum at idle but at throttle, correct? So, I should run the vacuum line straight to manifold vacuum, right. I read on one of the Corvette forums and they were saying the first Tri powers had the vacuum advance straight to the manifold vacuum.
i believe the quickfuel aftermarket metering block does have a provision for a vacuum advance. might be worth looking at.
Posted By: Hemi_Joel

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 06:00 PM

Originally Posted by polyspheric
For engines close to stock tune (any size, but mild cam) full vacuum to the distributor works well.
As the cam approaches 240 degrees @ .050", full vacuum works at idle, but as you open the throttle vacuum quickly dies, which reduces RPM, etc.
Ported fixes this, since idle is based solely on initial advance it's completely stable until a later throttle position.
You can even fab a new port position by inserting a small tube right through the casting to a point (generally slightly higher to delay vacuum) than the original, which will not add vacuum until slightly higher throttle disc angle. Hint: doesn't need to be horizontal.
Try both, keep the one that works best, cap the other (don't blank it), it may help the next time you change your tune-up.


Good point, but mostly applicable to stock initial timing settings. If you run your initial timing at 15 to 20°, where it should be for a performance motor, there's still plenty of advance to prevent the motor from bogging or stumbling when the vacuum advance goes away upon throttle tip in.

If you run ported vacuum to your advance can, you still have the same ignition timing at low vacuum conditions that you would with manifold vacuum, except you give up the clean idle.
Posted By: Cab_Burge

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 07:18 PM

I started working is Service Station, AKA Gas stations in 1961 and learn most of what I learn to work on cars back then.
All the Chevy cars that came in for tune ups that i remember had manifold vacuum for the vacuum advances, you had to disconnect them and cap off the port to set the initial timing is what I remembering now work Not so on the Fords and Mopars shruggy
I do remember also that GM swap to ported vacuum some time after 1961 shruggy
Posted By: DrCharles

Re: Is Vaccum Advance Really Such a Bad Idea - 02/14/21 07:36 PM

Originally Posted by polyspheric
For engines close to stock tune (any size, but mild cam) full vacuum to the distributor works well.
As the cam approaches 240 degrees @ .050", full vacuum works at idle, but as you open the throttle vacuum quickly dies, which reduces RPM, etc.
Ported fixes this, since idle is based solely on initial advance it's completely stable until a later throttle position.


With a relatively small cam of 240@.050, that may be true. It's definitely not the case with my 272@.050 which idles at only 8" vacuum. Lumpy but stable with 27 degrees at idle.
The vacuum can doesn't even move at 8", but at cruise (15" Hg) it's advanced, which is exactly when the engine wants it. So it's working fine on manifold vac.

Everybody's setup is different and I agree experimenting is important.
Posted By: jwb123

Re: Is Vaccum Advance Really Such a Bad Idea - 02/15/21 01:49 AM

for what it is worth, I agree on a street engine an advance curve is what you want to make it driveable. I approach it this way, I use an engine program, that among other things will calculate an advance curve for the engine combination that I have. It also calculates what rpm ranges detonation will be a problem. So if you don't have access to a distributor machine, the best way is to have a helper raise the rpm in 200 or so increments, use an adjustable timing light, note the timing on some graph paper and connect the dots. If you are using a vacuum advance I like one of those hand pumps with a gauge to see what the advance unit does. Then I change springs or what ever method the distributor uses to try and make my graph match the computer program recommendations. It usually is close. Then fine tune from there.
Posted By: SomeCarGuy

Re: Is Vaccum Advance Really Such a Bad Idea - 02/15/21 05:40 PM

About 15 years ago on here I had guys ready to fist fight over me merely saying it was good to run. Maybe after years of seeing others say it works people have seen the light. Been a few topics like that over the years on here.
Posted By: SomeCarGuy

Re: Is Vaccum Advance Really Such a Bad Idea - 02/15/21 05:43 PM

Originally Posted by jbc426
I ran my RB locked out at 35*, and the motor loved it. It never hard started hot or exhibited detonation. I too wanted to add vacuum advance, and came across a relatively new distributor from Progressive Ignition that had a fully adjustable digital vacuum advance feature in terms of total added and at what vacuum. The rest of the distributor's timing adjustment was digital as well.

I now have the start timing set at 21, idle and total timing set at 35* and at high manifold vacuum it goes up to 42* with the addition of the vacuum advance.

I bought one and installed it last year. There is a small learning curve as far as set-up and dialing in, but it was quick and easy to learn, as I can see where the timing is in real time while driving the car around. Yes, I too follow the Four Seconds Flat method of hooking the advance to manifold vacuum.

Here's the link:

https://progressionignition.com/shop/ols/categories/chrysler


Those are really interesting and I believe you posted that before maybe last year. I’m interested in the durability of them since most anything electronic these days seems to fail easily. The features seem really cool on these.
Posted By: Hemi_Joel

Re: Is Vaccum Advance Really Such a Bad Idea - 02/15/21 05:47 PM

Originally Posted by jbc426
I ran my RB locked out at 35*, and the motor loved it. It never hard started hot or exhibited detonation.

https://progressionignition.com/shop/ols/categories/chrysler


not every motor wants to crank over and start at 35 degrees locked. What was your compression ratio?
Posted By: hooziewhatsit

Re: Is Vaccum Advance Really Such a Bad Idea - 02/15/21 06:38 PM

Vac advance will work fine on ported or manifold, but it needs to be set up and tuned specifically for the method used.

It won't work to just move the vacuum line and call it a day.

Personally I used manifold vacuum on my truck. From memory, I have ~14° initial, plus around 20 mechanical (reduced/limited from what stock allowed), plus another 15ish via vac advance. During cranking it sees the initial 14 and starts well, then goes to 30 something. At part throttle cruise, they all add up to ~50 something. At wot, the vac advance drops out to the ~34 total. Keep in mind most vac cans can be adjusted as to what vacuum they drop out at, which also makes a difference and also needs to be tuned.

Works great, and really cleaned up my idle.

I think stock called for ~5 degrees initial timing, then had an enormous amount of mechanical advance, which must be limited if you want to run more initial.
Posted By: ZIPPY

Re: Is Vaccum Advance Really Such a Bad Idea - 02/15/21 07:20 PM

I'll admit I never spent much time to try to dial in vacuum advance B/C I have had too many problems with those vacuum cans leaking.
I've run a quick curve for many years and it works all right, but there are improvements to be had that deserve a little more time and effort.

I have heard of overheating and fuel economy problems from not using it, but haven't really noticed much.

Originally Posted by DaveRS23
Maybe an episode of Engine Masters?


Seems like they run everything locked out?
Idle and WOT power on a dyno: "What else is there?" seems to be the attitude, LOL.
Dulcich/Frieburger both used to stop by here once in awhile, like 20 years ago.
Posted By: furious70

Re: Is Vaccum Advance Really Such a Bad Idea - 02/16/21 01:23 AM

Originally Posted by ZIPPY
I'll admit I never spent much time to try to dial in vacuum advance B/C I have had too many problems with those vacuum cans leaking.
I've run a quick curve for many years and it works all right, but there are improvements to be had that deserve a little more time and effort.

I have heard of overheating and fuel economy problems from not using it, but haven't really noticed much.

Originally Posted by DaveRS23
Maybe an episode of Engine Masters?


Seems like they run everything locked out?
Idle and WOT power on a dyno: "What else is there?" seems to be the attitude, LOL.
Dulcich/Frieburger both used to stop by here once in awhile, like 20 years ago.


well, they did the long/short hemi intake comparison to look at area under the curve smile
Posted By: polyspheric

Re: Is Vaccum Advance Really Such a Bad Idea - 02/16/21 02:03 AM

The dangerous part is when you have big vacuum advance, but it doesn't go off as quickly as you would like - result: destructive knock (even for a second or two).
Rather than tune it with an adjustable can (Crane etc.): a small air solenoid (I use Bimba, it's 3/4" OD, 1-7/8" long and cheap) in the hose right at the can shuts down in .1-.2 seconds when the micro-switch on your throttle linkage hits, or you can use a button on your shifter.
Yes, there will always be a delay while the plate relaxes to normal position, not sure if a stronger spring is OK.
For sustained light throttle cruising, 60 years ago J.C. Whitney, Warshawsky, Honest Charley, etc. used to sell a thumb wheel with a cable attached. Device goes on your dash, cable moves the advance plate through the original can's linkage hole. To use: watch your vacuum gauge and move it to get the highest reading. Depending on your cam and gearing, higher speed may need more or less advance. Yes, for those WOT bursts you have to invent a quick disengage so you don't have to thumb it 10 times.
If you like to fab, a mechanical solenoid can pull and release a similar cable from Position A (relaxed) to Position B (+20 degrees) instantly with a strong return spring. If it's on a bell-crank, different linkage holes allow choosing among several advance levels.
Cables: quality products only, lube well, only large bends, adjustable for slack. Your bike shop has some choices.
Posted By: lewtot184

Re: Is Vaccum Advance Really Such a Bad Idea - 02/16/21 02:13 AM

i doubt an engine dyno would give any real world info. setting up a performance curve with a vacuum advance isn't straight forward and seems to be specific to each engine/car/driving combo. i know i must've built more than 20 different combos, and still aren't perfectly satisfied with one engine combo. what works on one won't work on the other. i don't glean much from the magazine guys anymore. i do believe that the factory mopar distributor and factory vacuum units are the best to work with. finding usable springs and plates could be a challenge. the FBO plates i have are far from accurate. i don't think the general motors clone distributors are as flexible as factory mopar.
Posted By: Hemi_Joel

Re: Is Vaccum Advance Really Such a Bad Idea - 02/16/21 03:06 AM

What I do is get the initial, mechanical, and total all dialed in for wide open throttle. Vacuum disconnected. Then hook up the vacuum and street drive it. Test part throttle pulls in various situations with the vacuum advance unrestricted and listen for pinging. Keep dialing it back a little and re-testing until it doesn't ping under any circumstance and you're done. Then disconnect and plug it when going racing.
Posted By: ZIPPY

Re: Is Vaccum Advance Really Such a Bad Idea - 02/16/21 02:30 PM

Originally Posted by furious70
Originally Posted by ZIPPY
I'll admit I never spent much time to try to dial in vacuum advance B/C I have had too many problems with those vacuum cans leaking.
I've run a quick curve for many years and it works all right, but there are improvements to be had that deserve a little more time and effort.

I have heard of overheating and fuel economy problems from not using it, but haven't really noticed much.

Originally Posted by DaveRS23
Maybe an episode of Engine Masters?


Seems like they run everything locked out?
Idle and WOT power on a dyno: "What else is there?" seems to be the attitude, LOL.
Dulcich/Frieburger both used to stop by here once in awhile, like 20 years ago.


well, they did the long/short hemi intake comparison to look at area under the curve smile


.....at wide open throttle wink
Posted By: Diplomat360

Re: Is Vaccum Advance Really Such a Bad Idea - 02/16/21 03:34 PM

Originally Posted by hooziewhatsit
Vac advance will work fine on ported or manifold, but it needs to be set up and tuned specifically for the method used.

Personally I used manifold vacuum on my truck. From memory, I have ~14° initial, plus around 20 mechanical (reduced/limited from what stock allowed), plus another 15ish via vac advance. During cranking it sees the initial 14 and starts well, then goes to 30 something. At part throttle cruise, they all add up to ~50 something. At wot, the vac advance drops out to the ~34 total.

Works great, and really cleaned up my idle.

You know, this seems like a great recipe well worth trying out. I can certainly appreciate cleaning up the idle situation, my 360 with just a 238@0.050 duration struggled with this for a long time. I re-worked the Carter TQ circuits which greatly improved this, but I bet there is still a little more left in there given that the engine would run ever-so-nicer with more advance at idle, and yet the problem with startup with that much initial advance would prevent me from going further.

Nice setup! punkrocka
Posted By: jbc426

Re: Is Vaccum Advance Really Such a Bad Idea - 02/16/21 04:13 PM

Originally Posted by Hemi_Joel
Originally Posted by jbc426
I ran my RB locked out at 35*, and the motor loved it. It never hard started hot or exhibited detonation.

https://progressionignition.com/shop/ols/categories/chrysler


not every motor wants to crank over and start at 35 degrees locked. What was your compression ratio?


True. My RB is calculated to be 10.2 to 1. It cranks 200 psi. Same ratio and cranking compression on my 408 Magnum. Both are high quench.
Posted By: jbc426

Re: Is Vaccum Advance Really Such a Bad Idea - 02/16/21 04:16 PM

Originally Posted by SomeCarGuy
Originally Posted by jbc426
I ran my RB locked out at 35*, and the motor loved it. It never hard started hot or exhibited detonation. I too wanted to add vacuum advance, and came across a relatively new distributor from Progressive Ignition that had a fully adjustable digital vacuum advance feature in terms of total added and at what vacuum. The rest of the distributor's timing adjustment was digital as well.

I now have the start timing set at 21, idle and total timing set at 35* and at high manifold vacuum it goes up to 42* with the addition of the vacuum advance.

I bought one and installed it last year. There is a small learning curve as far as set-up and dialing in, but it was quick and easy to learn, as I can see where the timing is in real time while driving the car around. Yes, I too follow the Four Seconds Flat method of hooking the advance to manifold vacuum.

Here's the link:

https://progressionignition.com/shop/ols/categories/chrysler


Those are really interesting and I believe you posted that before maybe last year. I’m interested in the durability of them since most anything electronic these days seems to fail easily. The features seem really cool on these.


Time will tell, but so far so good. I keep my MSD stuff in the trunk just in case.
Posted By: lewtot184

Re: Is Vaccum Advance Really Such a Bad Idea - 02/16/21 04:42 PM

Originally Posted by polyspheric
The dangerous part is when you have big vacuum advance, but it doesn't go off as quickly as you would like - result: destructive knock (even for a second or two).
Rather than tune it with an adjustable can (Crane etc.): a small air solenoid (I use Bimba, it's 3/4" OD, 1-7/8" long and cheap) in the hose right at the can shuts down in .1-.2 seconds when the micro-switch on your throttle linkage hits, or you can use a button on your shifter.
Yes, there will always be a delay while the plate relaxes to normal position, not sure if a stronger spring is OK.
For sustained light throttle cruising, 60 years ago J.C. Whitney, Warshawsky, Honest Charley, etc. used to sell a thumb wheel with a cable attached. Device goes on your dash, cable moves the advance plate through the original can's linkage hole. To use: watch your vacuum gauge and move it to get the highest reading. Depending on your cam and gearing, higher speed may need more or less advance. Yes, for those WOT bursts you have to invent a quick disengage so you don't have to thumb it 10 times.
If you like to fab, a mechanical solenoid can pull and release a similar cable from Position A (relaxed) to Position B (+20 degrees) instantly with a strong return spring. If it's on a bell-crank, different linkage holes allow choosing among several advance levels.
Cables: quality products only, lube well, only large bends, adjustable for slack. Your bike shop has some choices.
i took a que from the factory distributors and use a primary/secondary mech advance to stage the mech timing. the factory vacuum cans are adjustable and that's a big help. i also limit the amount of vacuum advance in the units to try to keep total for mech and vacuum to about 50degrees. i adjust the vacuum opening to around 10" of vacuum so anything under 10" diminishes the vacuum advance quickly. a fly in the ointment here is there are 3 different types of springs used in the canisters. i much prefer the 9 degree factory units over any aftermarket and they use the medium spring. so far this works for what i have but i think the key to all this is how much vacuum the engine makes. my experience has been the higher vacuum (stock type engines) are more temperamental than lower vacuum performance engines.
Posted By: DaveRS23

Re: Is Vaccum Advance Really Such a Bad Idea - 02/16/21 04:49 PM

Most of my experience has been with our big blocks and Hemis. I have messed with a some small blocks, but have much more time with the BBs and Hemis which really respond to ignition advance so this is directed primarily at the BBs and Hemis.

I don't really understand the place that manifold vacuum has in this. Our big blocks/Hemis like a lot of lead at idle and the bigger the cam the more lead they like. They also like the advance in as soon as can be, but kept out of detonation. That is the part where for me, the manifold source fails. It drops advance at a time that my experience shows that the engine wants it.

On my street combos, I typically run 25+* of initial. As much as I can and it still not hit the starter on hot days. And then all in by 2,000. On the wedges the total is usually 32* to 34*. On my current Hemi, it likes 31* for what ever reason. As I said before, I use a hand held vacuum pump to experiment with how much it likes at cruise. The change in exhaust note is very noticeable as you change the amount of advance and is a good starting point to set the amount of advance for cruise.

I use a stock Mopar distributor and JB Weld the slots to get the amount of advance that it likes. I also use JB Weld to add weight to the advance weights along with micro springs from a hardware store to get the rate right. It takes some trial and error and multiple disassemblies of the distributor, but after a time or two, it goes pretty quick.

For me, the toughest part is getting the vacuum can stop at the right place. The opening point is easy of course, since Mopar made that adjustable. There used to be a wide selection of vacuum cans with different amounts of vacuum advance. But that is not true anymore, so modifying what we have or can get is the way to go.

So my preferred mix is modifying the weights and springs in the distributor to get the initial timing and the mechanical advance where the engine is happy and then using ported vacuum for a modified vacuum advance. That's the way Mopar did it and the way that has worked very well for me forever. twocents
Posted By: lewtot184

Re: Is Vaccum Advance Really Such a Bad Idea - 02/16/21 06:09 PM

Originally Posted by DaveRS23
Most of my experience has been with our big blocks and Hemis. I have messed with a some small blocks, but have much more time with the BBs and Hemis which really respond to ignition advance so this is directed primarily at the BBs and Hemis.

I don't really understand the place that manifold vacuum has in this. Our big blocks/Hemis like a lot of lead at idle and the bigger the cam the more lead they like. They also like the advance in as soon as can be, but kept out of detonation. That is the part where for me, the manifold source fails. It drops advance at a time that my experience shows that the engine wants it.

On my street combos, I typically run 25+* of initial. As much as I can and it still not hit the starter on hot days. And then all in by 2,000. On the wedges the total is usually 32* to 34*. On my current Hemi, it likes 31* for what ever reason. As I said before, I use a hand held vacuum pump to experiment with how much it likes at cruise. The change in exhaust note is very noticeable as you change the amount of advance and is a good starting point to set the amount of advance for cruise.

I use a stock Mopar distributor and JB Weld the slots to get the amount of advance that it likes. I also use JB Weld to add weight to the advance weights along with micro springs from a hardware store to get the rate right. It takes some trial and error and multiple disassemblies of the distributor, but after a time or two, it goes pretty quick.

For me, the toughest part is getting the vacuum can stop at the right place. The opening point is easy of course, since Mopar made that adjustable. There used to be a wide selection of vacuum cans with different amounts of vacuum advance. But that is not true anymore, so modifying what we have or can get is the way to go.

So my preferred mix is modifying the weights and springs in the distributor to get the initial timing and the mechanical advance where the engine is happy and then using ported vacuum for a modified vacuum advance. That's the way Mopar did it and the way that has worked very well for me forever. twocents
the base of the stem of the vacuum advance has a notch in it. the length of the notch is how many distributor degrees are in the can. i haven't hit this exactly but about .011"-.012" travel in that notch is one distributor degree. i will limit the travel by gluing a shim on the canister to limit stem travel at the notch. i use permatex ultra gray silicone so i change the shims if i don't like them. i try to limit travel to 6-7 distributor degrees. mech advance has .0154" inches of travel for every one distributor degree.
Posted By: Mopar Mitch

Re: Is Vaccum Advance Really Such a Bad Idea - 02/16/21 07:30 PM

There was some previous talk in this thread about the PROMAX metering block not having the vacuum port.. and that is what I'm using... about 8 years ago, they (Promax) told me that I didn't need the port for the vacuum advance. They knew my driving -- some street/highway and road course HPDE/HSAX autocross racing... so, yes, it has lots of part-throttle, only occasional flat-out WOT. The car runs great -- and also now with a new SB stroker if still runs great (SB six-pack recently professionally rebuilt).

When I was ordering the Promax setup (base plates, etc, etc), they wanted to know all my specs, etc. They said they would make the metering block to better match my overall setup.... I'm an easy sell.

But... I'm curious if I should put the original OE/Holley metering block WITH the vacuum port back on and see how it would run.

Interesting thread.

(Maybe the Quick-Fuel metering block WITH the vacuum port would have been the better choice?)
Posted By: DaveRS23

Re: Is Vaccum Advance Really Such a Bad Idea - 02/16/21 07:46 PM

[/quote]the base of the stem of the vacuum advance has a notch in it. the length of the notch is how many distributor degrees are in the can. i haven't hit this exactly but about .011"-.012" travel in that notch is one distributor degree. i will limit the travel by gluing a shim on the canister to limit stem travel at the notch. i use permatex ultra gray silicone so i change the shims if i don't like them. i try to limit travel to 6-7 distributor degrees. mech advance has .0154" inches of travel for every one distributor degree. [/quote]

Good info, thanks.
Posted By: DaveRS23

Re: Is Vaccum Advance Really Such a Bad Idea - 02/16/21 07:51 PM

Is ProMax till around? Send it back to them or find someone else to add the port. Adding a vacuum port to the metering block shouldn't be a big deal. That may be better than putting an entirely different metering block on.
Posted By: lewtot184

Re: Is Vaccum Advance Really Such a Bad Idea - 02/16/21 07:54 PM

Originally Posted by Mopar Mitch
There was some previous talk in this thread about the PROMAX metering block not having the vacuum port.. and that is what I'm using... about 8 years ago, they (Promax) told me that I didn't need the port for the vacuum advance. They knew my driving -- some street/highway and road course HPDE/HSAX autocross racing... so, yes, it has lots of part-throttle, only occasional flat-out WOT. The car runs great -- and also now with a new SB stroker if still runs great (SB six-pack recently professionally rebuilt).

When I was ordering the Promax setup (base plates, etc, etc), they wanted to know all my specs, etc. They said they would make the metering block to better match my overall setup.... I'm an easy sell.

But... I'm curious if I should put the original OE/Holley metering block WITH the vacuum port back on and see how it would run.

Interesting thread.

(Maybe the Quick-Fuel metering block WITH the vacuum port would have been the better choice?)
my guess is that promax wants all the info to set-up idle jets and emulsion bleeds. the problem with the factory metering block is the idle jet inside the main metering well. it's too small in relation to the idle air bleed. the idle jet can be replaced or opened up but an easier solution you may want to try for a vacuum advance may be the quickfuel qft-34-8qft metering block. i'm pretty certain they have the ported vacuum provision and replaceable idle jet. if i ever get back into 6paks this is something i'll try. i never did the promax stuff because i never seen the need worth the expense. i just have a do it yourself mindset minus the gadgetry.
Posted By: mopower440

Re: Is Vaccum Advance Really Such a Bad Idea - 02/18/21 01:24 AM

I was undecided on manifold or port vacuum and i was about to buy a distributor from one of 2 people that set them up on a machine to your combo. I ended up with the one set up for port vacuum but i wish i would have went with the manifold vacuum because the idle stinks like hell with the 284/484 cam and the manifold vacuum may have cleaned that up a bit..
Posted By: lewtot184

Re: Is Vaccum Advance Really Such a Bad Idea - 02/18/21 01:37 AM

Originally Posted by DaveRS23
Is ProMax till around? Send it back to them or find someone else to add the port. Adding a vacuum port to the metering block shouldn't be a big deal. That may be better than putting an entirely different metering block on.

i haven't looked at the promax metering block in a while but i'm pretty sure the channel for the vacuum port nipple isn't machined in their blocks. without that channel a vacuum advance port nipple can't be installed. their metering block is more orientated toward the race crowd.
Posted By: lewtot184

Re: Is Vaccum Advance Really Such a Bad Idea - 02/18/21 01:43 AM

Originally Posted by mopower440
I was undecided on manifold or port vacuum and i was about to buy a distributor from one of 2 people that set them up on a machine to your combo. I ended up with the one set up for port vacuum but i wish i would have went with the manifold vacuum because the idle stinks like hell with the 284/484 cam and the manifold vacuum may have cleaned that up a bit..
there's no reason why you can't try manifold vacuum if you want. i'm a port vacuum guy, but if engine vacuum is fairly low manifold vacuum use may be the best choice. i have to wonder if your distributor is set-up for proper initial and low rpm centrifugal timing. the 284/484 is fairly aggressive with the 108lsa and a hydraulic tappet doesn't help much.
Posted By: mopower440

Re: Is Vaccum Advance Really Such a Bad Idea - 02/18/21 02:36 AM

Originally Posted by lewtot184
Originally Posted by mopower440
I was undecided on manifold or port vacuum and i was about to buy a distributor from one of 2 people that set them up on a machine to your combo. I ended up with the one set up for port vacuum but i wish i would have went with the manifold vacuum because the idle stinks like hell with the 284/484 cam and the manifold vacuum may have cleaned that up a bit..
there's no reason why you can't try manifold vacuum if you want. i'm a port vacuum guy, but if engine vacuum is fairly low manifold vacuum use may be the best choice. i have to wonder if your distributor is set-up for proper initial and low rpm centrifugal timing. the 284/484 is fairly aggressive with the 108lsa and a hydraulic tappet doesn't help much.


Its supposed to be. I havent had a chance to try it yet. I have my current one at 18 initial and 34 total with no vacuum advance and it screams. I cant advance the total any more or it pings.Its all in by 2800 which could stand to be slowed down some. I wanted one custom curved to my combo with the vacuum advance so i had a guy on another mopar site build me one, which i have not tried yet due to icy roads. The current one i did runs great but like i was saying, i wanted the vacuum working and dialed in.
Posted By: DaveRS23

Re: Is Vaccum Advance Really Such a Bad Idea - 02/18/21 03:00 PM

18* initial sure isn't much with any cam at all.

If it were mine, I would want more initial than that. And it seems to me that the best route would be to shorten the advance slots. Can someone explain why manifold vacuum would be a better solution in this case than more initial in the distributor?
Posted By: lewtot184

Re: Is Vaccum Advance Really Such a Bad Idea - 02/18/21 04:08 PM

manifold vacuum isn't necessarily better, but with a given set of parts and low vacuum to begin with somebody may not have a choice. i always use ported but who am i to say manifold vacuum is off the table. i have one set-up on one of my cars that uses a 9 degree plate with 36 degrees total. i use a light primary spring that begins the centrifugal fairly quick and idle is about 23 degrees even though i know the initial is 18 degrees. my other car won't tolerate this kind of timing and this is why i believe that curves have to be individually set-up per engine/car/driver. i think it wouldn't be easy to buy something from a vendor, even if they have all the info, that will be perfectly tailored for an individuals combo.
Posted By: hooziewhatsit

Re: Is Vaccum Advance Really Such a Bad Idea - 02/18/21 04:58 PM

Originally Posted by DaveRS23
18* initial sure isn't much with any cam at all.

If it were mine, I would want more initial than that. And it seems to me that the best route would be to shorten the advance slots. Can someone explain why manifold vacuum would be a better solution in this case than more initial in the distributor?


I think the main concern is whether the engine can crank and start with too much initial.

If the engine likes 20+ initial timing, but can't crank with that much, pretty much the only option is to use manifold vacuum to give a lower initial, or some sort of start retard box.

If it does crank fine with 20+, then sure, limit the advance slots, and set the initial at 20+.


Also in general, the engine vacuum at idle needs to be higher than the vacuum in the advance (if using manifold). If they're similar, then the timing will change with vacuum, which changes the vacuum, which changes the idle speed, which change.... panic It will never settle down and be steady. Similar issue if the step up springs in an Edelbrock are the same as the idle vacuum.
Posted By: DrCharles

Re: Is Vaccum Advance Really Such a Bad Idea - 02/18/21 07:48 PM

Originally Posted by hooziewhatsit
If the engine likes 20+ initial timing, but can't crank with that much, pretty much the only option is to use manifold vacuum to give a lower initial, or some sort of start retard box.

If it does crank fine with 20+, then sure, limit the advance slots, and set the initial at 20+.


Or you can do what I did... one superlight spring, one heavier spring with loop. Initial timing is 16, but when the engine starts it immediately goes to the end of the loop which is 27 degrees idle timing. Slow advance to 36 after that (limited by rotor tower/plate).

Quote
Also in general, the engine vacuum at idle needs to be higher than the vacuum in the advance (if using manifold). If they're similar, then the timing will change with vacuum, which changes the vacuum, which changes the idle speed, which change.... panic It will never settle down and be steady. Similar issue if the step up springs in an Edelbrock are the same as the idle vacuum.


True about the unstable idle (same with centrifugal advance coming in too early). But it also works if the idle vacuum is lower than the can (again, like mine). 8" at idle and the can does not move. At cruise (15") it's all in.
Posted By: hooziewhatsit

Re: Is Vaccum Advance Really Such a Bad Idea - 02/18/21 09:54 PM

Oh, both of those are true up
Posted By: DaveRS23

Re: Is Vaccum Advance Really Such a Bad Idea - 02/18/21 11:45 PM

I think if it were mine, I would experiment with twisting the distributor to find the limits of initial when it starts to hit against the starter and then give it all it would take by shortening the slots.

Using either mechanical or vacuum advance to bring up the idle timing would very likely end up having a guy chasing his tail as you pointed out. Just putting it into gear or easing the clutch out would change the RPM/vacuum and thereby the idle speed/quality.
Posted By: dannysbee

Re: Is Vaccum Advance Really Such a Bad Idea - 02/19/21 04:53 AM

I’m using a Mopar tach drive distributor. I’m going to try this with it.
https://www.cbperformance.com/default.asp
Posted By: Cab_Burge

Re: Is Vaccum Advance Really Such a Bad Idea - 02/19/21 06:34 AM

Originally Posted by dannysbee
I’m using a Mopar tach drive distributor. I’m going to try this with it.
https://www.cbperformance.com/default.asp
Try what?
Posted By: madscientist

Re: Is Vaccum Advance Really Such a Bad Idea - 02/19/21 02:05 PM

Originally Posted by Cab_Burge
Originally Posted by dannysbee
I’m using a Mopar tach drive distributor. I’m going to try this with it.
https://www.cbperformance.com/default.asp
Try what?


LOL...I didn’t find anything from that link except a website with a bunch of pages to sort through. I certainly want to see what he is going to try.
Posted By: DaveRS23

Re: Is Vaccum Advance Really Such a Bad Idea - 02/19/21 02:34 PM

All I saw on that site was air cooler Volkswagon stuff.
Posted By: dragon slayer

Re: Is Vaccum Advance Really Such a Bad Idea - 02/19/21 03:33 PM

I think for a race car folks keep it simple. These discussions on other sites go on for 10s of pages. While folks understand all the individual piece, not sure folks have thought through all the integrated elements. Some times vacuum adv advances for motor needs, other times it retards timing.

Most know generically what vacuum does, but I doubt many have mapped vacuum under driving conditions.

For HP motors with dual points in the day, before emissions you would have around 8 to 12 degrees initial, and get another 16-22 out of the mechanical, with a light and heavy (gapped) spring. Vacuum added or takes away another 18-24 degrees. Stock motor, stock calibrated carb designed for the motor and the distributor. Once CAP hit in 66-67 initial was between -2 to +2 usually around 0 for BB certainly hemi. Mechanical gave 30 degrees, some unit 34. Vacuum still around 22.

So as you go down this path, what changes have you made. What is engine vacuum look like intake/ported. When does ported come in, or is it already on at idle because of cam, carb change and other things tuning changes you made for idle.

Seems a little dangerous to have a high initial, and vacuum on intake, especially if you made changes to mechanical adv springs to get all in earlier. As stated earlier, even when vacuum goes toward 0, the vacuum timing retards slower, and with mechanical advancing faster, your probably pretty close to detonation.
If your doing this in your drive way in neutral your really not testing a loaded motor.
Posted By: DaveRS23

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 12:53 AM

None of my vacuum advance units have ever retarded the timing. They drop out their added advance when vacuum drops, but the timing only returns to the initial or mechanical advance. I haven't had one retard the timing beyond that.

Determining what the engine likes is not that difficult with a tach, timing light, and a hand held vacuum pump.
Posted By: Cab_Burge

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 01:57 AM

Some of the Mopar ECU will retard the ignition timing a little (1 to 2 degrees per 1000 RPM above 5000 RPM :scope) above 5000 RPM shruggy
when I first started paying attention to drag race tuning a lot of the faster racers had a switch to turn off one set of points to retard the ignition timing in high gear shruggy
It seems like some of the street and strip MSD boxes would also, maybe not as i never used them confused
Posted By: 440_Offroader

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 02:02 AM

Originally Posted by dannysbee
I’m using a Mopar tach drive distributor. I’m going to try this with it.
https://www.cbperformance.com/default.asp


Is this what you were referring to?

https://www.cbperformance.com/CB-s-Black-Box-Programmable-Timing-Control-Module-p/2013.htm
Posted By: Diplomat360

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 04:59 AM

For all of you talking about having to shorten the advance slots, or make 'em longer, etc. etc...there is a far easier solution...this setup has been out for some time now and if you haven't picked this type of a distributor up yet, well, if the right price comes up it's well worth it. You simply use a plastic gauge to measure out how far to slide the plates in the distributor around (there is a gap provided already).

[Linked Image]

It is my understanding Mallory has been making this setup for MP for a few years now. The bonus is that you have a pile of adjustability (curve wise) with their spring kit...fast, slow, mid, etc., all the variations. That's kit# 29014.

That's what I have setup in my coupe right now.
Posted By: DaveRS23

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 02:28 PM

The kit you list appears to be for Mallory distributors. Not a lot of guys have those. The reviews for the kit are not stellar. And the kits do not seem to be available....anywhere.

And finally, this thread is about vacuum advance but the distributor you suggest doesn't even have vacuum advance. shruggy
Posted By: madscientist

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 02:32 PM

Originally Posted by Cab_Burge
Some of the Mopar ECU will retard the ignition timing a little (1 to 2 degrees per 1000 RPM above 5000 RPM :scope) above 5000 RPM shruggy
when I first started paying attention to drag race tuning a lot of the faster racers had a switch to turn off one set of points to retard the ignition timing in high gear shruggy
It seems like some of the street and strip MSD boxes would also, maybe not as i never used them confused



ALL ignition boxes retard with RPM. All of them. The best box I’ve tested for that is a early 1980’s DC Gold Box. It retards 1 degree in 10,000 RPM. I think it took 8,000 RPM to get that.

I just tested a well know box for street stuff and it retards 6 or 7 degrees (I can’t remember if that box was 6 or 7 because I tested 5 boxes that day and that one was one of the boxes that had the most retard) and IIRC started retarding at about 4,000 or so and kept retarding to 8,000.
Posted By: dragon slayer

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 02:51 PM

Originally Posted by DaveRS23
None of my vacuum advance units have ever retarded the timing. They drop out their added advance when vacuum drops, but the timing only returns to the initial or mechanical advance. I haven't had one retard the timing beyond that.

Determining what the engine likes is not that difficult with a tach, timing light, and a hand held vacuum pump.


I am talking total timing. Dropping out is retarding. Your cruising on the highway at part throttle. What is vacuum? How much of your total timing is mech and how much is vacuum? What happens when you punch it to pass? Vacuum goes away and total timing retards. The motor does not want all that timing under load and starting to accelerate. As RPM climbs mechanical runs up and vacuum timing is 0 and your at your total around 32-34. Prior you where probably around 44-46 total timing maybe more. The vacuum can adjust time up and down based on load. Mechanical adjust up and down based on RPM of motor. Both are factors in determining what timing is needed for peak efficiency.

Go read the Chrysler master training material on this. That will explain what the Chrysler engineers were doing, and why things changed for emissions. It really explains what the motor needs at various operating conditions.

So I have read were some race guys use a low adv vacuum can to help their car idle after start. The high initial keeps car from starting hot. So they dial back initial to start hot, but vacuum can on manifold gets total back to were it is needed for idle. Once they get on it, the vacuum drops out and they are on the mechanical. So you use it as you thing your combo needs it. Manifold versus ported is basically an on off switch for the vac can. Ported is off at idle an on at a specific point of throttle blade opening. Manifold is on all the time.
Posted By: 6PakBee

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 02:58 PM

Originally Posted by dragon slayer
Originally Posted by DaveRS23
None of my vacuum advance units have ever retarded the timing. They drop out their added advance when vacuum drops, but the timing only returns to the initial or mechanical advance. I haven't had one retard the timing beyond that.

Determining what the engine likes is not that difficult with a tach, timing light, and a hand held vacuum pump.


I am talking total timing. Dropping out is retarding. Your cruising on the highway at part throttle. What is vacuum? How much of your total timing is mech and how much is vacuum? What happens when you punch it to pass? Vacuum goes away and total timing retards. The motor does not want all that timing under load and starting to accelerate. As RPM climbs mechanical runs up and vacuum timing is 0 and your at your total around 32-34. Prior you where probably around 44-46 total timing maybe more. The vacuum can adjust time up and down based on load. Mechanical adjust up and down based on RPM of motor. Both are factors in determining what timing is needed for peak efficiency.

Go read the Chrysler master training material on this. That will explain what the Chrysler engineers were doing, and why things changed for emissions. It really explains what the motor needs at various operating conditions.

So I have read were some race guys use a low adv vacuum can to help their car idle after start. The high initial keeps car from starting hot. So they dial back initial to start hot, but vacuum can on manifold gets total back to were it is needed for idle. Once they get on it, the vacuum drops out and they are on the mechanical. So you use it as you thing your combo needs it. Manifold versus ported is basically an on off switch for the vac can. Ported is off at idle an on at a specific point of throttle blade opening. Manifold is on all the time.


George, do you have a link for this?
Posted By: dragon slayer

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 03:06 PM

http://www.imperialclub.com/Repair/Lit/Master/index.htm

These are great reads and a wealth of information.
Posted By: 6PakBee

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 03:13 PM

Originally Posted by dragon slayer
http://www.imperialclub.com/Repair/Lit/Master/index.htm

These are great reads and a wealth of information.


Wow. Thanks. up I have a number of Master Technician booklets from the day and they are a wealth of information.
Posted By: Diplomat360

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 03:23 PM

DaveRS23,

Originally Posted by DaveRS23
The kit you list appears to be for Mallory distributors. Not a lot of guys have those. The reviews for the kit are not stellar. And the kits do not seem to be available....anywhere.

And finally, this thread is about vacuum advance but the distributor you suggest doesn't even have vacuum advance. shruggy

Well, as I stated in my post, it was my understanding that Mallory became the distributor supplier to MP some years ago. The pic shows the guts, the focus being the adjustability given the design of the sliding plates. This setup has the VAC can provisions, it being a regular MP distributor replacement.

I went that route some years ago, have the kit here, the VAC can hooked up, all that. Working great for me, for what it's worth!

Bummer if the kit is out of production b/c it is pretty handy.
Posted By: DaveRS23

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 04:01 PM

What does your training materials say about tuning 500 inches, big cams, open plenum intakes, Dominator carbs, straight through exhaust, etc, etc? Good info to know, but not necessarily pertinent. Chrysler engineers had to make many, many compromises to accommodate every idiot with a payment book. Not necessarily what was best for the engine or even for peak performance at the time. Let alone half a century later.

This is a discussion of semantics. Retarding vs dropping out. Maybe the same thing, but to say that the vacuum advance retards timing could be confusing for those that are not as familiar with the function. To describe the vacuum can's function as advancing and dropping out that advance is just more explanatory. Saying that the vacuum can advances and retards the timing could lead someone to believe that it could take the timing both above and below the mechanical timing. It may be technically correct, but is not as clear.

With all the mods going on with our cars, it is possible that some unique combos, particularly drag cars, could benefit from manifold vacuum. But for most street combos, dialing in the distributor and adding a tuned vacuum advance with ported vacuum is the way to go.
Posted By: Moparite

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 04:43 PM

Quote
it is possible that some unique combos, particularly drag cars, could benefit from manifold vacuum.

No, Manifold vacuum drops to nothing as soon as the throttle opens. See post #2888120
Posted By: bee1971

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 04:54 PM

Originally Posted by madscientist
Originally Posted by Cab_Burge
Some of the Mopar ECU will retard the ignition timing a little (1 to 2 degrees per 1000 RPM above 5000 RPM :scope) above 5000 RPM shruggy
when I first started paying attention to drag race tuning a lot of the faster racers had a switch to turn off one set of points to retard the ignition timing in high gear shruggy
It seems like some of the street and strip MSD boxes would also, maybe not as i never used them confused



ALL ignition boxes retard with RPM. All of them. The best box I’ve tested for that is a early 1980’s DC Gold Box. It retards 1 degree in 10,000 RPM. I think it took 8,000 RPM to get that.

I just tested a well know box for street stuff and it retards 6 or 7 degrees (I can’t remember if that box was 6 or 7 because I tested 5 boxes that day and that one was one of the boxes that had the most retard) and IIRC started retarding at about 4,000 or so and kept retarding to 8,000.


Are we talking MSD boxes etc. or Mopar ECUs / Ignition Modules that like came from the factory 1972 and later ?



I literally have tested a handful on my 71 Superbee 383/432 Stroker , and none of these Chinese knockoffs , fake transistor ECUs , work well over 5,000 RPMs - Like mentioned a few start failing at 4,000 RPMs

Really had me digging deep over a few summers

My 1990s Mopar Performance Chrome ECU was the best unit , until that failed a few years back

Now I have some brand new never mounted Standard LX101s from 1986 and 1987 that where made in the USA I need to try out


I remember reading this some years back

https://www.hotrod.com/articles/mopp-1211-3-2-1-ignition-box/
Posted By: DaveRS23

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 05:08 PM

Originally Posted by Moparite
Quote
it is possible that some unique combos, particularly drag cars, could benefit from manifold vacuum.

No, Manifold vacuum drops to nothing as soon as the throttle opens. See post #2888120


I have never seen a situation where the manifold would be the best source for vacuum advance. But I did not want to make the statement that it was never the best place.
Posted By: bee1971

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 05:12 PM

So far so good with the Jegs / Firecore Distributor
Has the adjustable mechanical slots / numerous springs / and adjustable vacuum advance

I run ported vacuum

I can adjust the mechanical advance with the distributor in the engine using different size drill bits , very easy

https://www.jegs.com/i/JEGS/555/40504/10002/-1#
Posted By: dragon slayer

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 05:17 PM

Originally Posted by DaveRS23
What does your training materials say about tuning 500 inches, big cams, open plenum intakes, Dominator carbs, straight through exhaust, etc, etc? Good info to know, but not necessarily pertinent. Chrysler engineers had to make many, many compromises to accommodate every idiot with a payment book. Not necessarily what was best for the engine or even for peak performance at the time. Let alone half a century later.

This is a discussion of semantics. Retarding vs dropping out. Maybe the same thing, but to say that the vacuum advance retards timing could be confusing for those that are not as familiar with the function. To describe the vacuum can's function as advancing and dropping out that advance is just more explanatory. Saying that the vacuum can advances and retards the timing could lead someone to believe that it could take the timing both above and below the mechanical timing. It may be technically correct, but is not as clear.

With all the mods going on with our cars, it is possible that some unique combos, particularly drag cars, could benefit from manifold vacuum. But for most street combos, dialing in the distributor and adding a tuned vacuum advance with ported vacuum is the way to go.



Ok, Chrysler engineers just did things for idiots??? What does that even mean? It is not my semantics, it is the words the Chrysler engineer used. Yes the vacuum can reduce timing certainly below the mechanical. You are in the Racers forum, I think they can understand what was said.

My only point was this is a total integrated product. Too many variables can be changed and folks don't always recognize how they have changed the SLOPE of the timing curve when you add a vacuum can. You seem to be trying to simplify the solution.

In general, springs are linear. With an inflection point as the heavy spring is applied when the loop closes up. You can control when they apply, and rate of advance with a spring change and total amount of mech adv by cam stop plate. Without a vac can you move up and down that timing line based purely on RPM.

With vacuum can it is not just moving further up the line, you now have a variable slope depending on acceleration or deacceleration and load. Your RPM timing is now different under different conditions because vacuum adv may be going lower or higher depending on load.

For a street car you need a device that can advance timing more then the car can handle when under WOT and full load. You don't want 55 total timing at WOT and your not efficient at cruise with 34. And yes and engine is an engine. The principles and engineering laws have not changed because displacement increased and a cam was added. Principles are the same.

It is more pertinent to discuss the use of the car rather then the size of the motor. Street, Strip or both. Yes, no (unless solving a problem), yes (maybe). There is a ton of cars out there running no vacuum or running plugged. The car will still run and perform.
Posted By: dragon slayer

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 05:27 PM

Originally Posted by Moparite
Quote
it is possible that some unique combos, particularly drag cars, could benefit from manifold vacuum.

No, Manifold vacuum drops to nothing as soon as the throttle opens. See post #2888120


I gave one...hot starts on a race car that needs a lot of advance to idle. But cannot start with that much initial.

Above statement is not correct. You still have vacuum and now you have it at the ported position and they both are about equal. Vacuum lowers though.

Now under WOT and load vacuum goes to near zero, but guess what, so does ported. It is exposed to manifold vacuum because throttle blades are open.

Ported is a switch. Normal stock cars designed on ported (Chrysler). There is no vacuum to the cannister until the throttle blades open enough to expose the carburetor port to manifold vacuum. Turn your idle up to about 2K and you will probably see ported vacuum turn on and start advancing timing. That is why you remove the hose when setting initial timing.

Posted By: DaveRS23

Re: Is Vaccum Advance Really Such a Bad Idea - 02/20/21 07:08 PM

Well, you are welcome to your opinion.

Chrysler often had to engineer things just because of idiots. Manufacturers still do today. To deny that is to deny reality. Although they have never achieved true 'idiot proof' status, they do try.

And I do not agree that our typical Mopar vacuum advance cans retard timing below the mechanical. You accuse me of oversimplifying this, but you are really making this much more complicated and difficult than it needs to be. In fact, you are down right confusing.

It is vacuum advance. Been around since the 50s. A tach, timing light, hand held vacuum pump and a little knowledge and you are good to go. Shouldn't be above most guy's pay grade. Unless they make it way more complicated than it really is.

Posted By: dannysbee

Re: Is Vaccum Advance Really Such a Bad Idea - 02/22/21 12:29 AM

It’s in the ignition section. It’s called the black box and it’s a programmable vacuum advance.
https://www.cbperformance.com/CB-s-Black-Box-Programmable-Timing-Control-Module-p/2013.htm
Posted By: DaveRS23

Re: Is Vaccum Advance Really Such a Bad Idea - 02/22/21 03:20 PM

That is certainly an interesting timing box. First time I have seen it and the only videos I can find has it on 4 banger air cooled VWs. Their website says it is V8 compatible, but it would be nice to actually see it on them. $200 seems a bit steep just to control timing. And the initial set-up is more than a little convoluted: www.youtube.com/watch?v=E9dWYOe8Utg

That may be a good alternative for someone a bit more computer literate than myself and who cannot re-curve the distributor and tune the vacuum advance.
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