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Old 09-22-2019, 01:09 PM   #21
Ol' Ron
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Default Re: timing advance how much is to much

I run 28 in cruise.
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Old 09-22-2019, 02:01 PM   #22
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Default Re: timing advance how much is to much

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I run 28 in cruise.
Yes, but that's with a vacuum advance/retard distributor isn't it Ron? The vacuum advance/retard capability allows for more total advance in a cruise condition (high vacuum) and pulling it off in an acceleration condition (low vacuum). So, with say 10 degrees of vacuum advance the total advance would be around 18 degree accelerating.
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Old 09-22-2019, 09:43 PM   #23
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Default Re: timing advance how much is to much

Yes, the engine in my truck is a "stock" 280ci engine, a former 276 with rusty cylinders. I put a stock cam in it and bored it .020 with new Egge pistons. Now with the milled EAB heads I have aprox 8.2 CR so I can burn a lean mixture in cruise, But WOT is only 20 degs. This winter I plan on modifying a set of 8BA heads to see how small of a combustion chamber I can make with out running the flow. Might have some Brazing in the future.
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Old 09-23-2019, 08:35 AM   #24
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Default Re: timing advance how much is to much

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Yes, the engine in my truck is a "stock" 280ci engine, a former 276 with rusty cylinders. I put a stock cam in it and bored it .020 with new Egge pistons. Now with the milled EAB heads I have aprox 8.2 CR so I can burn a lean mixture in cruise, But WOT is only 20 degs. This winter I plan on modifying a set of 8BA heads to see how small of a combustion chamber I can make with out running the flow. Might have some Brazing in the future.
Ron , i think your 28 is a overlap of vacuum with mechanical..Vac is high and you have x amount and then vac drops and mech advance is high= x.
The typical vac advance is 14 degrees and the mech is 14 ( using a example) the 14 and 14 overlap as you cant have both at the same time . ( the reason for vac advance to start with) Engine then has 17 total all the time , thats the logic for using the vacuum....is that right ???
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Old 09-23-2019, 11:58 AM   #25
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Default Re: timing advance how much is to much

Why can't you have full vacuum and full mechanical at the same time? If you have the mechanical all in in at say 2000 rpm, at light load you'll still be pulling 16 - 18 in hg.
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Old 09-23-2019, 12:20 PM   #26
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Default Re: timing advance how much is to much

I agree with flatjack9. I agree with Bubba that the two advances do overlap, at times. I think you can have both at the same time. My 276" with a L100 cruises at 2500 rpm with vacuum of 17". The spec on the vacuum canister is all in at 13". Why wouldn't the mechanical and the vacuum be cumulative?
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Old 09-23-2019, 12:57 PM   #27
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Default Re: timing advance how much is to much

Exactly.
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Old 09-23-2019, 01:22 PM   #28
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Default Re: timing advance how much is to much

If you have centrifugal advance weights and your vacuum advance chamber is attached to the breaker plate. They work independently. The weights work on RPM, only. Then the breaker plate advances with vacuum, increasing the advance, given by the weights.

So, you have initial advance, plus centrifugal advance, plus vacuum advance. Each one changes the the total advance as it is designed to.
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Old 09-23-2019, 01:50 PM   #29
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Default Re: timing advance how much is to much

In reality, how it works, is that you set your initial, then with the vacuum advance, unpluged, rev the engine to 2000 or, what ever the book gives as max advance RPM and check the total advance. Then adjust the initial advance, to what you want or, what the factory says the total advance should be.

The vacuum advance is a economizer and is not available under load.

I set my total advance, before the engine goes in the car, with a degree wheel. You find TDC, on the wheel, then move it to what you want the total advance to be. You then twist the weights, to full advance. With a ohm meter hook to the points, you rotate the distributor until you see the points break, with the ohm meter.

Lock it down and you have it set for max advance. The only setting that counts, for max power.

While you have the degree wheel on the engine, you would mark the pulley for TDC and total advance, using a convenient pointer, to align with the marks.

Add more marks, if you like, for initial timing but those two are what you really need.
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Old 09-23-2019, 01:55 PM   #30
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Default Re: timing advance how much is to much

When I was a mechanic, on our Sun diagnostic machine, the timing light had a knob and once you reached total advance, you could turn the knob to align the light to the TDC timing mark and then be able to read the total advance. Not the norm for old hot rodders but, it works, too.
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Old 09-23-2019, 02:55 PM   #31
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Default Re: timing advance how much is to much

I have 20* at 2000 mechanical. 8* in the vacuum can. In cruise I usually turm between 2/2300 rpm. I set the AF at around 15+ Hard to get with the 2GC. Using 51 jets now. PV drops it to 12.8/13.1

I have a megasquirt universal engine management computer that was given to me. I've picked up a GM throttle body from a 90/96 truck/ I have a 4bl intake I can mount the TB and just run the computer for AF and Ignition timing. Got too many projects going for my age, and i feel like a roll of toilet paper. I;d jut like to know the limits of this tuning sh*t. Get fom facts, everybody has a different slant on it
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Old 09-23-2019, 04:17 PM   #32
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Default Re: timing advance how much is to much

Frnkore , I think you explained that real good ,
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Old 09-23-2019, 05:28 PM   #33
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Default Re: timing advance how much is to much

"ol' Ron" - You constantly amaze me. I have to say that what you are talking about (Megasquirt) is about the last thing I am thinking about these days".
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Old 09-23-2019, 07:06 PM   #34
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Default Re: timing advance how much is to much

Thank you, Ted.
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Old 09-23-2019, 07:18 PM   #35
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Default Re: timing advance how much is to much

You can get good vacuum and good mech with rpm. The discussion is forgetting the word load .
With load its very hard to have proper rpm and vac at the same time ,

expecially on a flathead.. I agree with all thats been said , a good set up with a vac can will get ya 2-3 mpg ....
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Old 09-23-2019, 07:19 PM   #36
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Default Re: timing advance how much is to much

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Frnkore , I think you explained that real good ,
I agree good explanation...
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Old 09-23-2019, 09:08 PM   #37
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Default Re: timing advance how much is to much

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Originally Posted by BUBBAS IGNITION View Post
You can get good vacuum and good mech with rpm. The discussion is forgetting the word load .
With load its very hard to have proper rpm and vac at the same time ,

expecially on a flathead.. I agree with all thats been said , a good set up with a vac can will get ya 2-3 mpg ....
Why would the flathead be any harder than any other engine? Most systems are a compromise. Engines are so much better today because they are controlled electronically.
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Old 09-24-2019, 07:03 AM   #38
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Default Re: timing advance how much is to much

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Why would the flathead be any harder than any other engine? Most systems are a compromise. Engines are so much better today because they are controlled electronically.
I think the flatheads are very different as they are pretty low cubic inch engines with the valves are in the engine block.

Just went to a car show this weekend and they had a new 840 horse power Dodge Demon drive in.

I agree the engines today are very much better today.
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Old 09-24-2019, 11:20 AM   #39
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Default Re: timing advance how much is to much

I've never had the opportunity to play with a "Stock" 239 engine, and if I had one in the 3400 lb truck, it would certainly have an affect on the tuning. I got the truck (47 Int.) back in 84, ran it stock f or a few years. Engine, steering and brakes were junk. So I replaced them with a 52 front axle, a 51 Merc engine and Merc o matic. 3.3 rqr xle. I needed a truck for my business. All this was stock and lasted for about 10 years with little or no problems. I replaced the Merc with a 350/350 Chevy and that lasted until I decided to install a blown flathead in it. Unfortunately, my Partner at the time passed away, and I got evicted from the shop. THe property was put up for sale in 06. and here I am. Putzin!!!
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Old 09-24-2019, 10:06 PM   #40
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Default Re: timing advance how much is to much

Is it fair to say timing and tuning is separate or the same. You can't time an engine with vacuum only if the top end is funky or leaking. Both are needed ultimately under load.



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