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Re: vacuum advance on 110hp...best practice?
Posted by: Frank DuVal ()
Date: September 26, 2022 06:58AM

Also, what emissions regulation was Chevrolet trying to meet on the old Stovebolts back in the 40s? They also ran ported vacuum to the distributor! That's why I say this ported vacuum is only to meet emission regulations is historically inaccurate!eye popping smiley

Hard to remove that steel vacuum line to set timing... It is threaded fittings at both ends.

[www.chevytalk.org]

Frank DuVal

Fredericksburg, VA



Edited 1 time(s). Last edit at 09/26/2022 06:59AM by Frank DuVal.

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Re: vacuum advance on 110hp...best practice?
Posted by: potvinguy ()
Date: September 26, 2022 12:03PM

Frank DuVal Wrote:
-------------------------------------------------------
> 110 with PCV valve? AC car? Or 110 in an earlier vehicle (pre 64)?

It's not a conventional PCV valve, but just a "fixed orifice", I.E., a pinhole. A hose connects from the manifold balance tube to the hose that goes from the crankcase to the air cleaner. I guess the idea was to suck some of the crankcase fumes into the balance tube and on into the manifolds to be burned. The orifice is somewhere in that tangle of hoses. Looks like more of the emission stuff they were trying back then.

Page 61 of the Clark's catalog has diagrams: PCV and such



Edited 2 time(s). Last edit at 09/26/2022 12:12PM by potvinguy.

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Re: vacuum advance on 110hp...best practice?
Posted by: PequotMonza64 ()
Date: September 26, 2022 01:52PM

Maybe I'm missing something here, but I thought that at idle there was not supposed to be any advance - neither mechanical or vacuum. I thought those advanced were supposed only factory in when load or rpm or both were factored in.

If you have full vacuum advance on at idle won't it RETARD as you step on the gas pedal?

Also, what are you guys using to measure 24 or 45 degrees of timing on a Corvair engine? Not a timing light. Whatever tool you are using needs a mechanical reference. I'm aware that some harmonic balancers have a scale on them.

Glen in Ohio
1964 Monza Sedan Powerglide 110 hp
Low mileage survivor, stock as delivered
Records back to 1967 in Pequot Lakes, Minnesota
Original dealer Mike Turk's in East Liverpool, Ohio
Located in Cleveland, Ohio area


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Re: vacuum advance on 110hp...best practice?
Posted by: potvinguy ()
Date: September 26, 2022 02:31PM

PequotMonza64 Wrote:
-------------------------------------------------------
> Maybe I'm missing something here, but I thought that at idle there was not supposed to be any advance - neither mechanical or vacuum. I thought those advanced were supposed only factory in when load or rpm or both were factored in.
>
> If you have full vacuum advance on at idle won't it RETARD as you step on the gas pedal?
>
> Also, what are you guys using to measure 24 or 45 degrees of timing on a Corvair engine? Not a timing light. Whatever tool you are using needs a mechanical reference. I'm aware that some harmonic balancers have a scale on them.

At idle you should have full vacuum advance and no mechanical advance. Vacuum advance compensates for engine load by advancing spark when load is low (and it is lowest at idle). As load increases vacuum advance decreases. Mechanical advance compensates for engine rpm and increases as rpm increases.

To measure timing we use a digital or dial-back light like this one.dialback light



Edited 2 time(s). Last edit at 09/26/2022 02:32PM by potvinguy.

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Re: vacuum advance on 110hp...best practice?
Posted by: PequotMonza64 ()
Date: September 26, 2022 02:44PM

potvinguy Wrote:

> At idle you should have full vacuum advance and no mechanical advance. Vacuum advance compensates for engine load by advancing spark when load is low (and it is lowest at idle). As load increases vacuum advance decreases. Mechanical advance compensates for engine rpm and increases as rpm increases.
>

I thought you had max vacuum at idle. Isn't that why you're supposed to disable vacuum advance and plug the advance vacuum hose at idle? You want the vacuum advance to be disabled when adjusting idle.

I'm not sure I understand how there can be two (or more) schools of thought on this subject. It certainly would be helpful if people would restrict this discussion to Corvair engines and also to respect that the Turbo is its own beast. I think the original poster was asking about a bread and butter 110 hp engine.

Glen in Ohio
1964 Monza Sedan Powerglide 110 hp
Low mileage survivor, stock as delivered
Records back to 1967 in Pequot Lakes, Minnesota
Original dealer Mike Turk's in East Liverpool, Ohio
Located in Cleveland, Ohio area


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Re: vacuum advance on 110hp...best practice?
Posted by: wittsend ()
Date: September 26, 2022 03:00PM

PequotMonza64 Wrote:
-------------------------------------------------------
>...
> If you have full vacuum advance on at idle won't it RETARD as you step on the gas pedal?
>
> Also, what are you guys using to measure 24 or 45 degrees of timing on a Corvair engine? Not a timing light. Whatever tool you are using needs a mechanical reference. I'm aware that some harmonic balancers have a scale on them.

That is correct having full vacuum advance (manifold) at idle will cause it to drop when accelerating. Ported vacuum (the way GM and most car manufactures designed it) comes in at a certain point after the throttle has opened from idle.

The POTENIAL problem is that if you use the vacuum advance at idle it will require turning the idle speed down to its normal setting. You then run the risk of the RPMs dropping as the vacuum advance (and thus the timing) falls off upon acceleration POTENTIALLY to a level below what is common with ported vacuum.

The other POTENTIAL problem is instead of the vacuum dropping and the RPM's falling below normal is the vacuum resides higher than normal and there is too much advance on the engine causing ping or detonation. The other thing is that under full throttle there is no vacuum advance. But if you lowered (static/mechanical) the timing for ping or detonation caused by the manifold vacuum advance you effectively have less timing overall.

I'm careful to use the word POTENTIAL because these things may not happen. Remember that a manufacture has to warranty the engine and the engine has to run in many different climates under varying loads, and many different elevations. So, is there room to "cheat" a little more power out of an engine -YES! Is it wise under any circumstance, No. The requirements for a near sea level car, on a cool/cold day with only the driver aboard, on a level road are quite different from someone at an 8,000 ft. elevation, on a hot day, a car full of people and luggage, going up hill.

From GM's reasoning and that of others it is wrong to use manifold vacuum. That doesn't mean that some have used it without consequences but it shouldn't be a blanket prescription for everyone as was somewhat implied in the original post.

Regarding reading higher advance markings there are calibrated adhesive tapes that have a higher number of measured degrees that can be applied to harmonic balancers. The issues is that the tape needs to be calibrated to the diameter of the balancer. I do not know if any exist for a Corvair. Since the Corvair has the markings on the cover you would reference zero on the tape to zero on the Corvair cover and then use zero as your reference point to what the tape was showing.

As an economical means you could use Calipers to reference say, 5 or 10 degrees and then using difference colored paint markings denote those on the balancer again referencing to zero when reading the actual advance. There is however, nor guarantee of accuracy.

------------------------------------------------------------------------------

***'61 Lakewood, a "Freebie" in hibernation for 27 years - In the process of applying CPR.***

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Re: vacuum advance on 110hp...best practice?
Posted by: potvinguy ()
Date: September 26, 2022 03:01PM

Glen, I feel your pain. Timing, particularly vacuum advance, seems to make people crazy. It shouldn't, because the science is quite simple.

I always adjust idle with the vacuum advance operating; if you disable it and set idle, then when you plug it back in the idle is gonna jump up.

I am the OP with my stock 110 motor. But all ICEs obey the same physics regardless of number of cylinders, V or flat, etc. Here's a paper that some guy wrote to explain it.



Edited 1 time(s). Last edit at 09/26/2022 03:01PM by potvinguy.

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Re: vacuum advance on 110hp...best practice?
Posted by: potvinguy ()
Date: September 26, 2022 03:19PM

Here's another article on timing. It does confuse AFR and AF density, but still gives the right info.

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Re: vacuum advance on 110hp...best practice?
Posted by: PequotMonza64 ()
Date: September 26, 2022 03:58PM

Something to keep in mind when we're posting is to remember that some people here are doing magical non-standard things to their cars while others are just trying to establish a baseline benchmark with a car that's been messed with by various people over the years.

I'm currently happy to have sorted all of my engine issues and gotten to a situation where my engine responds as expected to instruction from GM and Bob Helt. I had a carb with some sort of deep internal fault that stumped the previous owner and stumped me, as well. After rebuilding it more than once, I smartened up and spent the net $162 for a rebuilt one from Clark's. Oh, the wasted (if educational) hours I spent on that.

Then I found photos that finally showed me that my harmonic balancer was shifted about 40 degrees and walking toward my oil filter. The rubber was like brand new, and as many times as I read that the marks had to line up, no one ever said that there were THREE marks not TWO that had to line up. Imagine how much time I spent playing with that.

Now, if I want to try something a little bit non-standard, I'm in a position to do so. I think, however, I'm going to try and get it just as good as I can with standard tuning method , and then see about going further.

Glen in Ohio
1964 Monza Sedan Powerglide 110 hp
Low mileage survivor, stock as delivered
Records back to 1967 in Pequot Lakes, Minnesota
Original dealer Mike Turk's in East Liverpool, Ohio
Located in Cleveland, Ohio area


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Re: vacuum advance on 110hp...best practice?
Posted by: red monza ()
Date: September 26, 2022 08:15PM

I believe the orig poster mentioned he had an idle issue but when he hooked up to a constant vacuum supply, his engine responded in a positive manner and smoothed out nicely. It does not matter if you have a 4, 6, 8, 10, 12, or 16 cylinder engine they all operate the same way in older cars. You have static advance, vacuum advance, and mechanical advance. My post was to tell the gentleman it was okay to have full time vacuum as my 283 also operated best like that. It is always comforting to know someone else has done it and it worked fine.

If one reads the books on timing, think about this...it states to disconnect the vacuum advance and plug it...what does that mean? It means that it is getting vacuum from the engine already and advancing the timing on its own. I believe that tells me also its already using the engines vacuum regardless where its connected and that it is perfectly fine to advance the timing with vacuum...agreed? Static timing in a Corvair can be 4 to 24 degrees. I think some carbs do not produce any vac advance and no need to disconnect or block to set the static timing with a low idle speed. Check the timing with it hooked up and not hooked to see your circumstance.

"Chevy made 34 different distributors for the Corvair, all interchange. but will give undesirable results if the incorrect distributor is used". Remember what I said about the 339 dist I bought that had mostly 298 dist parts in it.

What most books say about timing for Corvairs...actually almost any engine, even Fords and, yes, 283's even included, is to have a total of 37-38 degrees of total advance. I marked my Corvair H/B once to give a total of 40 degrees reading. There is a simple way but can't remember exactly now how to. Anyway, the only ones that count is the static at about 20 and 18 on the mechanical, my 140 was really close as I remember but did not go over the 40 mark. I did not change anything as it runs strong like that.

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Re: vacuum advance on 110hp...best practice?
Posted by: 63turbo ()
Date: September 26, 2022 08:33PM

PequotMonza64 Wrote:
-------------------------------------------------------
> Maybe I'm missing something here, but I thought that at idle there was not supposed to be any advance - neither mechanical or vacuum. I thought those advanced were supposed only factory in when load or rpm or both were factored in.
>
> If you have full vacuum advance on at idle won't it RETARD as you step on the gas pedal?
>

Yes this happens, but just because the vacuum advance is going away doesnt mean the power drops! ideally the vacuum timing keeps the engine at full power for the vacuum level, so as the vacuum goes away, the timing is falling only enough to be a good match for the current manifold pressure... remember, it takes time for the air to rush into the canistor and change the timing, and it also takes time for the air to rush into the engine. The bugger with those mechanical based timing controls is that they were severly compromised and never really track what the engine really needs, both because they dont respond fast enough, and because the resulting curve just isnt the right shape for all the possibiltys. Its one vacuum advance curve for all rpms, and because of the wild possible changes in volumetric efficiency, cant possibly be right for all situations with one VA curve. It WILL be wrong somewhere and one of those "somewhere's" is the point at which they stop adding any timing. On Corvair VA's this is somewhere in the neighborhood of 5 to 7", which is a lot like the engine being at 5000 to 7000 ft in altitude... a lot less air is present at 5000-7000ft and wont develop as much power as it could if it is not timed for that. This part of the reason you can sometimes feel the engine bog if the load gets a teeny bit too much. This is one of the many reasons why programmable timing is so cool, you can get rid of those timing bugs that are friggin impossible to take care of with springs weights vacuum cansitors and a whole host of other "band aids".

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car
Test Start#2 [www.youtube.com]



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Re: vacuum advance on 110hp...best practice?
Posted by: PequotMonza64 ()
Date: September 26, 2022 08:35PM

red monza Wrote:
-------------------------------------------------------
> I believe that tells me also its already using the engines vacuum regardless where its connected and that it is perfectly fine to advance the timing with vacuum...agreed?

Not necessarily. How much vacuum and how much is needed to actuate the vacuum advance?

>Static timing in a Corvair can be 4 to 24 degrees.

That may be your experience, but that's not what's published in what I've read. My 110 with PG is 12 degrees. Maybe I've missed something. I have it set at 10 because a Corvair bud suggested it would be better on our available fuel.

> Anyway, the only ones that count is the static at about 20 ...

I'm sure you have much more experience tuning the engines, and I may need to be schooled, but that makes absolutely no sense to me.

Maybe later on I'll understand why what works for you seems to be so far from the norm. Maybe you forgot to mention you are not using factory standard parts in the standard configuration. In the meantime, I'll just assume that I'm still in the dark

Glen in Ohio
1964 Monza Sedan Powerglide 110 hp
Low mileage survivor, stock as delivered
Records back to 1967 in Pequot Lakes, Minnesota
Original dealer Mike Turk's in East Liverpool, Ohio
Located in Cleveland, Ohio area


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Re: vacuum advance on 110hp...best practice?
Posted by: Frank DuVal ()
Date: September 26, 2022 09:25PM

Quote
pot
I always adjust idle with the vacuum advance operating; if you disable it and set idle, then when you plug it back in the idle is gonna jump up.

Not on a correctly operating stock Corvair engine (or a Stovebolt six as I mentioned earlier). If the idle speeds up when reconnecting the vacuum advance, the carburetor throttle plates are open too much.

Quote
pot
> 110 with PCV valve? AC car? Or 110 in an earlier vehicle (pre 64)?

It's not a conventional PCV valve, but just a "fixed orifice", I.E., a pinhole. A hose connects from the manifold balance tube to the hose that goes from the crankcase to the air cleaner. I guess the idea was to suck some of the crankcase fumes into the balance tube and on into the manifolds to be burned. The orifice is somewhere in that tangle of hoses. Looks like more of the emission stuff they were trying back then.

Gee, you said PCV valve, that's why I asked the question. Of course I know what the PCV system is on a stock 110 or 95 HP engine is. Sounds like you have an issue with trying to make engines run cleaner for our health. Do you understand what a PCV system does? It is not a hinderance to a properly operating engine. It scavenges the vapors in the crankcase, burning them in the engine rather than spraying the fumes out in the open like the road draft tube did. Also, the road draft tube did not do a good job of removing the vapors from the crankcase, causing sludging and other engine issues.

Hoses for PCV are easy to understand. The orifice is right in the side nipple on the horizontal tube. Don't make the hole bigger trying to clean it. Usually it is not really dirty unless it is a high milage engine.

Frank DuVal

Fredericksburg, VA

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Re: vacuum advance on 110hp...best practice?
Posted by: Frank DuVal ()
Date: September 26, 2022 09:34PM

Quote
Glen
Static timing in a Corvair can be 4 to 24 degrees.

That may be your experience, but that's not what's published in what I've read. My 110 with PG is 12 degrees. Maybe I've missed something. I have it set at 10 because a Corvair bud suggested it would be better on our available fuel.

Glen, he was saying over all the Corvair engines made, the factory specs ranged from 4 BTC to 24 BTC. 1961 80 HP manual transmission is 4 BTC and the turbos are 24 BTC.

You can step yours up to 12 and see if it pings, especially when the Powerglide just shifts into high.

Frank DuVal

Fredericksburg, VA

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Re: vacuum advance on 110hp...best practice?
Posted by: potvinguy ()
Date: September 26, 2022 09:45PM

Just a clarification: is "static timing" and "initial timing" the same thing? We should all be using the same nomenclature.



Edited 1 time(s). Last edit at 09/26/2022 09:46PM by potvinguy.

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Re: vacuum advance on 110hp...best practice?
Posted by: red monza ()
Date: September 27, 2022 07:10AM

potvinguy Wrote:
-------------------------------------------------------
> Just a clarification: is "static timing" and "initial timing" the same thing? We should all be using the same nomenclature.

Yes, same same. Who should we assign to be the "static" or "initial" police and make everyone use the same name for the same thing? Bob Helt says "static" for timing, I am with him, you others who call it "initial timing" report to the jail house please, lol lol.
Years back, here in NC, the "filling stations" or is it "gas stations" had "Hi Test" and regular gas, now called "Premium" and Regular. Same same.

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Re: vacuum advance on 110hp...best practice?
Posted by: PequotMonza64 ()
Date: September 27, 2022 07:16AM

potvinguy Wrote:
-------------------------------------------------------
> Just a clarification: is "static timing" and "initial timing" the same thing? We should all be using the same nomenclature.

I would think static timing would be the timing that is simply determined by the gearing and the position of the distributor with no modification by centrifugal advance or vacuum advance. Since that's where you normally set your baseline before adding in other factors, I guess you could call that initial timing.

However, if you are starting with the vacuum advance already connected and having an effect, it seems to me that you have skipped a step. I am assuming that connecting the vacuum advance to the non-ported vacuum would have an even stronger vacuum at idle than the ported vacuum, but I'm not clear on that.

I don't have that much experience with Corvair engines, but I have EXTENSIVE experience calibrating complex electronic systems with multiple analog feedback loops, and you always had to start at certain baselines and proceed in an orderly manner. Otherwise, you never knew where you stood. The system might function perfectly at one point in its range and look beautiful but be junk in every other point in its operating range.

I don't doubt that some people can use a seat of the pants approach based on extensive experience and end up with an engine tune they like. However, the title of this thread refers to best practices.

I maintain that there must be a proper procedure for setting up the timing that we all can agree with that's relatively straightforward and science-based. What setting you choose to use beyond that are at your personal option, meaning that if you are working to achieve a certain sort of curve you will choose your degree of advance, where you port your vacuum advance from and even which springs you have inside your distributor in the centrifugal advance.

I'll just follow the factory procedure to set a baseline and then do any sort of "customization" built upon that.

Glen in Ohio
1964 Monza Sedan Powerglide 110 hp
Low mileage survivor, stock as delivered
Records back to 1967 in Pequot Lakes, Minnesota
Original dealer Mike Turk's in East Liverpool, Ohio
Located in Cleveland, Ohio area


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Re: vacuum advance on 110hp...best practice?
Posted by: potvinguy ()
Date: September 27, 2022 07:41AM

Yes, Frank, PCV systems are good when they work. OEM PCV valves are calibrated to the engine they will be on. If the engine is modified so as to lower the manifold vacuum (say with a big cam), then the PCV valve may open at idle, not a good thing.

The SEMA guys sell generic PCV valves, all billet and shiny, but who knows their calibration? And fixed orifices are always drawing crankcase fumes into the engine, even at idle. Now this may not be a problem as long as the orifice is not so big that it is impossible to set the desired idle speed (the orifice or a wrong PCV valve is just like a vacuum leak) and the plugs don't foul.

There is a company Wagner that makes an adjustable PCV valve, which I use on my hot rod.

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Re: vacuum advance on 110hp...best practice?
Posted by: potvinguy ()
Date: September 27, 2022 07:47AM

PequotMonza64 Wrote:

>
> I don't have that much experience with Corvair engines, but I have EXTENSIVE experience calibrating complex electronic systems with multiple analog feedback loops, and you always had to start at certain baselines and proceed in an orderly manner.

Glen, did you by chance work in process control? I did for a while and it is a fascinating business.

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Re: vacuum advance on 110hp...best practice?
Posted by: potvinguy ()
Date: September 27, 2022 07:56AM

PequotMonza64 Wrote:
-------------------------------------------------------

>
> I maintain that there must be a proper procedure for setting up the timing that we all can agree with that's relatively straightforward and science-based.

Absolutely. Set initial timing at idle with no vacuum advance. Then rev the engine such that all mechanical advance is in and check the added advance. Then back at idle, connect the vacuum (manifold of course) and check the added advance. If the numbers match the book, then you are correct per GM. This procedure doesn't reveal the curves, but to do that takes more time and a tachometer and a vacuum gauge and a bit of OCD.

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