The Ford Barn

AKCJ · 01-13-2016, 01:07 PM

Great discussion guys. For my build (53, EAB shaved heads, 4" crank in a 50 shoebox) I'm planning to use the converted distributor. I think I want one with both mechanical and vacuum advance as I'd like to take advantage of the timing advance under light load. I have heard more than once that the flathead may not benefit much from this? And/or it's difficult to set up? Could someone explain the procedure to set up the vacuum advance. This would help me and probably many other guys.

flatheadmurre · 01-13-2016, 01:26 PM

Quote:

Originally Posted by AKCJ

Great discussion guys. For my build (53, EAB shaved heads, 4" crank in a 50 shoebox) I'm planning to use the converted distributor. I think I want one with both mechanical and vacuum advance as I'd like to take advantage of the timing advance under light load. I have heard more than once that the flathead may not benefit much from this? And/or it's difficult to set up? Could someone explain the procedure to set up the vacuum advance. This would help me and probably many other guys.

First you need to know the maximum limits you need for mech/vac.
Next is to install the right weights/springs to get a curve that fits the engine in your application.
Vacuum you can tweek around with different size of diaphragms and restrictors.
I would say shipping it of to Bubba and taking advantage of his skills is cheaper then the time you invest doing it yourself, if its not for learning.
And just about any distributor can be tweaked to fit a flathead just takes more or less job.

Richard in Florida · 01-13-2016, 03:51 PM

Quote:

Originally Posted by AKCJ

Could someone explain the procedure to set up the vacuum advance?

Converted GM distributors, both the early points version and the "big cap" HEI version, are very easy to adjust, even on the engine. The only thing you have to do to start adjusting is remove the cap and rotor. The springs and weights are right on top.

However, adjusting vacuum advance -- which I think is a real advantage to have -- can't be done with the distributor on the engine because you can't replicate the variations in vacuum while sitting in your driveway.

All the vacuum does is add some degrees (amount is up to you - I use 8 degrees) when manifold vacuum is high. This is great for cruise economy AND a cooler, smoother idle.

The trick is to set your vacuum advance using a simple fixture like you see below. This simple fixture lets me see and set both mechanical advance and vacuum advance; you need a vacuum pump for the vacuum.

I won't eat up space here describing the fixture in detail; it should be obvious. But I'll glad answer questions about it.

AKCJ · 01-14-2016, 12:15 PM

Richard - that's pretty cool! Thanks!

Richard in Florida · 01-14-2016, 04:08 PM

Quote:

Originally Posted by AKCJ

Richard - that's pretty cool! Thanks!

The upper pointer indicates mechanical advance, and the lower pointer reads vacuum advance.

The fixture is good for close ballparking, but final settings should be made on a distributor machine if at all possible.

Ol' Ron · 01-14-2016, 04:22 PM

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Richard is building a Frankenstein (Big cap) distributor for the Loudon Engine and has just informed me that the Phasing id very far off. And this id a GM Manufacturing error. Which I don't check very often. If something can go wrong, it will go wrong. Fortunately, it got fixed.

Richard in Florida · 01-14-2016, 05:30 PM

Quote:

Originally Posted by Ol' Ron

Richard is building a Frankenstein (Big cap) distributor for the Loudon Engine and has just informed me that the Phasing is very far off. And this is a GM Manufacturing error. Which I don't check very often. If something can go wrong, it will go wrong. Fortunately, it got fixed.

Actually, this is a problem with the Chinese ACCEL vacuum canisters. It's easily fixed by elongating the canister mounting holes.

Oh, and we're calling Ol' Ron's big cap Igor.

scooder · 01-15-2016, 08:44 AM

Richard,
What make is the vacuum can your using? As I understand some aftermarket cans are adjustable for vacuum value you want it to operate at, say 15"hg tunable down to 5"hg, and some do this aswell as limit the amount of timing they add, not all do both.
Thanks,
Martin.

Richard in Florida · 01-15-2016, 11:01 AM

Quote:

Originally Posted by scooder

Richard,
What make is the vacuum can your using? As I understand some aftermarket cans are adjustable for vacuum value you want it to operate at, say 15" hg tunable down to 5" hg, and some do this as well as limit the amount of timing they add, not all do both.

The most commonly adapted vacuum canister is from ACCEL but I think the same way-offshore factory packages the same canister for Crane and a few others but there's only one canister.

Vacuum canisters do only one thing: pull on the breaker plate or magnet/pickup coil inside the distributor. Claims of being able to set the amount of extra advance AND the rate at which it comes in I think are misleading. Only the amount is actually adjustable.

Stock non-adjustable canisters have various rates of vacuum vs pull-rod travel, but that rate is fixed for each model.

To my knowledge there is only one adjustable canister for the early Chevy points conversion, #31034, and one for the big cap Chevy HEI conversion, #31035, and the only thing adjustable is the distance the pull-rod travels.

tubman · 01-15-2016, 12:51 PM

The Corvette guys really have this SBC vacuum advance thing down pat. Some of the guys on the forums have spent a lot of time researching this stuff. I think Echlin still makes various advance units with specific "pull-in" levels that can be purchased at NAPA. If you can stand it, go over to the Corvette Forum and search for the "vacuum canisters" and you can glean a lot of information. I know their overall reputation, but there are a few serious tuners over there that do more than re-arrange their gold chains. They follow something called the "2 inch rule" that basically says the vacuum advance should start to come in at least 2 inches below the engine vacuum at idle (or cruise; I forget).

Lawson Cox · 01-15-2016, 01:19 PM

Way over my head fellows. LOL

BUBBAS IGNITION · 01-15-2016, 03:37 PM

Quote:

Originally Posted by richard in florida

the most commonly adapted vacuum canister is from accel but i think the same way-offshore factory packages the same canister for crane and a few others but there's only one canister.

Vacuum canisters do only one thing: Pull on the breaker plate or magnet/pickup coil inside the distributor. Claims of being able to set the amount of extra advance and the rate at which it comes in i think are misleading. Only the amount is actually adjustable.

Stock non-adjustable canisters have various rates of vacuum vs pull-rod travel, but that rate is fixed for each model.

To my knowledge there is only one adjustable canister for the early chevy points conversion, #31034, and one for the big cap chevy hei conversion, #31035, and the only thing adjustable is the distance the pull-rod travels.

kinda like this :

CA Victoria · 01-15-2016, 04:34 PM

I did a search and found this info on operation and identification of the different GM vacuum units. Interesting.....

http://www.corvette-restoration.com/...c_Adv_Spec.pdf

Lawrie · 01-15-2016, 05:26 PM

This is just a thought,
If you want to be able to adjust the amount of timing that the vacuum controls,could you not use a helmet or crab type distributor with the vac brake,you can use the 21a advance unit and they look a lot nicer fitted down on the front of the engine instead of that after thought up the top on the later engines.
Lawrie

Ol' Ron · 01-15-2016, 07:01 PM

The biggest problem with the early distributors is: there isn't any easy way to adjust the mechanical advance. You can grind down the springs and add or subtract weight. Inlarge the slots, etc. but it's still a crap shoot. The Delco unit on the other hand can be nade to accomplish almost any curve you can come up with. At present the springs are the most dificult to come up with, so Richard makes his own. But then again, he's kinda fussy.

Lawrie · 01-15-2016, 07:18 PM

Ron ,I knew after I posted, that was a problem,as I,m in the process of limiting the advance on a 40b advance,
On our old dragster engine we used to have an MSD set up ,that was so easy to change the curve or advance amount,
But the front mount distributors are nice though,like they are meant to be there,
Lawrie

Ol' Ron · 01-15-2016, 09:56 PM

On our stock car our first distributor had the advance plate welded up at 16 degs adv ( 11A) then we just set the initial where it ran best off the corners. To start the engine, we'd spin the starter before turning on the ignition. This worked quite well. WE then went to a SBC dist with the max adv at 17. The trouble with short track racing the engineisn't as important as the driver han handling.

01-13-2016, 01:07 PM	#41
AKCJ Member Join Date: Oct 2013 Location: Fairbanks, Alaska Posts: 92	Re: Ignition requirements Great discussion guys. For my build (53, EAB shaved heads, 4" crank in a 50 shoebox) I'm planning to use the converted distributor. I think I want one with both mechanical and vacuum advance as I'd like to take advantage of the timing advance under light load. I have heard more than once that the flathead may not benefit much from this? And/or it's difficult to set up? Could someone explain the procedure to set up the vacuum advance. This would help me and probably many other guys.

01-14-2016, 12:15 PM	#44
AKCJ Member Join Date: Oct 2013 Location: Fairbanks, Alaska Posts: 92	Re: Ignition requirements Richard - that's pretty cool! Thanks!

01-14-2016, 04:22 PM	#46
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,860	Re: Ignition requirements Sponsored Links (Register now to hide all advertisements) Richard is building a Frankenstein (Big cap) distributor for the Loudon Engine and has just informed me that the Phasing id very far off. And this id a GM Manufacturing error. Which I don't check very often. If something can go wrong, it will go wrong. Fortunately, it got fixed.

01-15-2016, 08:44 AM	#48
scooder Senior Member Join Date: Jul 2010 Posts: 2,593	Re: Ignition requirements Richard, What make is the vacuum can your using? As I understand some aftermarket cans are adjustable for vacuum value you want it to operate at, say 15"hg tunable down to 5"hg, and some do this aswell as limit the amount of timing they add, not all do both. Thanks, Martin.

01-15-2016, 12:51 PM	#50
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 10,319	Re: Ignition requirements The Corvette guys really have this SBC vacuum advance thing down pat. Some of the guys on the forums have spent a lot of time researching this stuff. I think Echlin still makes various advance units with specific "pull-in" levels that can be purchased at NAPA. If you can stand it, go over to the Corvette Forum and search for the "vacuum canisters" and you can glean a lot of information. I know their overall reputation, but there are a few serious tuners over there that do more than re-arrange their gold chains. They follow something called the "2 inch rule" that basically says the vacuum advance should start to come in at least 2 inches below the engine vacuum at idle (or cruise; I forget). Last edited by tubman; 01-15-2016 at 01:31 PM.

01-15-2016, 01:19 PM	#51
Lawson Cox Senior Member Join Date: May 2010 Location: Above the gnat line in Georgia Posts: 7,009	Re: Ignition requirements Way over my head fellows. LOL __________________ Life is like a roll of toilet paper. The closer to the end, the faster it goes. It is better to be seen, than viewed. "We sleep safe in our beds because rough men stand ready in the night to visit violence on those who would do us harm".

01-15-2016, 04:34 PM	#53
CA Victoria Senior Member Join Date: Feb 2011 Posts: 2,113	Re: Ignition requirements I did a search and found this info on operation and identification of the different GM vacuum units. Interesting..... http://www.corvette-restoration.com/...c_Adv_Spec.pdf __________________ Tim Downtown, Ca

01-15-2016, 05:26 PM	#54
Lawrie Senior Member Join Date: May 2010 Location: Qld, Australia Posts: 4,215	Re: Ignition requirements This is just a thought, If you want to be able to adjust the amount of timing that the vacuum controls,could you not use a helmet or crab type distributor with the vac brake,you can use the 21a advance unit and they look a lot nicer fitted down on the front of the engine instead of that after thought up the top on the later engines. Lawrie

01-15-2016, 07:01 PM	#55
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,860	Re: Ignition requirements The biggest problem with the early distributors is: there isn't any easy way to adjust the mechanical advance. You can grind down the springs and add or subtract weight. Inlarge the slots, etc. but it's still a crap shoot. The Delco unit on the other hand can be nade to accomplish almost any curve you can come up with. At present the springs are the most dificult to come up with, so Richard makes his own. But then again, he's kinda fussy.

01-15-2016, 07:18 PM	#56
Lawrie Senior Member Join Date: May 2010 Location: Qld, Australia Posts: 4,215	Re: Ignition requirements Ron ,I knew after I posted, that was a problem,as I,m in the process of limiting the advance on a 40b advance, On our old dragster engine we used to have an MSD set up ,that was so easy to change the curve or advance amount, But the front mount distributors are nice though,like they are meant to be there, Lawrie

01-15-2016, 09:56 PM	#57
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,860	Re: Ignition requirements On our stock car our first distributor had the advance plate welded up at 16 degs adv ( 11A) then we just set the initial where it ran best off the corners. To start the engine, we'd spin the starter before turning on the ignition. This worked quite well. WE then went to a SBC dist with the max adv at 17. The trouble with short track racing the engineisn't as important as the driver han handling.