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  #16 (permalink)  
Old 03-07-2005, 05:11 AM
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Alright.. Thanks.. So say if it pings with 2 2400's in then I should just go back up to a mix of a 2400 and a 3400 spring correct? Instead of going back up to 2 3400's.

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  #17 (permalink)  
Old 03-07-2005, 05:56 AM
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Trying to use your engine for a Distributor Machine can get frustrating and a little hard on the motor.

Sending your distributor to a qualified Ignition shop with years of experience and 5,000 successfully curved distributor will usually net you better results.

Even after you get it set up you wamt to spin it to the moon to be sure the advance mechanism in these aftermarket distributors don't jump timing and can hold the advance steady. There's some real junk out there in the market, be very careful on what you choose for your application, if your not sure consult with a professional and that's not some kid at a mail order house.

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The only time we have ever had a problem with Demon's has been due to debris somehow remaining in the casting assembly somewhere. On Demons we typically will disassemble and inspect prior to running on the dyno, just in case. Otherwise they perform well with very good brake specifics.

I understand fully, this is why we disassemble, inspect, clean and baseline set every Demon Carb before it leaves our shop. We charge $25.00 but when they leave here they compare to your experience with a Brazwell...few minor tuning adjustments and mash the loud peddle.
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  #18 (permalink)  
Old 03-07-2005, 10:32 AM
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cooling problems

I have a 79 Vette. The motor that was in it when I purchased it had the vac adv connected to the manifold and a Q Jet. I put a 375 HP 350 in the car with a Holley 4150 and have had overheating problems ever since. I am now installing a 400 sb. I have done everything I can think of to nix the cooling problems.

I read the first post on vacuum advance. I figured that hooking vacuum adv to manifold may help my cooling at idle.

I contacted Holley tech. They told me to use the port on the carb or the vac adv would come on right from idle and cause a flat spot.
Quote:
Distributor Tuning and Theory - Part 1
Holley does not agree with your theory.

Last edited by bracketeer; 03-07-2005 at 04:02 PM.
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Old 03-07-2005, 11:42 AM
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Well, as one who has ALWAYS pushed for "Ported vacuum" advances, i'll bite and say I've seen the light. Guess I'll go take the plug off my advance and try manifold and see how it goes.

Since everyone seems to now be on the same page here, i'll ask a question.
My truck is a 1/2 ton chevy, .030 350. 9.2 comp, cam is a Crane 276 ( I think). Headers, Q-jet, mild head work on my 882's with automatic tranny.

I run about 10 to 12 degrees initial timing, plus my weights push the timing to 35 full in by 2600rpm. My normal cruise speed in town is about 2100 and freeway is 2700@65mph. So....according to the article, I can use another 10+ degrees of vacuum advance at idle? My truck idles fine and does not overheat at all. Is this extra 10+ degrees really necessary in my case? Or is it overkill? I guess the plus side is more timing at cruise speed hopefully giving me a little better mileage. My biggest problem is actually hearing the pinging. I never do anymore since my hearing has gone south. Guess I'll have to take my son along for the testing.

Feedback welcome!!

Mark
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Old 03-07-2005, 03:03 PM
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Quote:
Originally Posted by Jmark
Well, as one who has ALWAYS pushed for "Ported vacuum" advances, i'll bite and say I've seen the light. Guess I'll go take the plug off my advance and try manifold and see how it goes.

Since everyone seems to now be on the same page here, i'll ask a question.
My truck is a 1/2 ton chevy, .030 350. 9.2 comp, cam is a Crane 276 ( I think). Headers, Q-jet, mild head work on my 882's with automatic tranny.

I run about 10 to 12 degrees initial timing, plus my weights push the timing to 35 full in by 2600rpm. My normal cruise speed in town is about 2100 and freeway is 2700@65mph. So....according to the article, I can use another 10+ degrees of vacuum advance at idle? My truck idles fine and does not overheat at all. Is this extra 10+ degrees really necessary in my case? Or is it overkill? I guess the plus side is more timing at cruise speed hopefully giving me a little better mileage. My biggest problem is actually hearing the pinging. I never do anymore since my hearing has gone south. Guess I'll have to take my son along for the testing.

Feedback welcome!!

Mark
From how I understand it. Because at cruise and idle the motor isn't under a load or much stress it can actually handle the extra 10 degrees of advance. I mean after all haven't we grown up with the idea of getting as much advance as possible without detonation? So since the engine is crusing along nicely without stress from hard accelleration, it can accept the extra timing more effeciently. But when you punch it, that's where ported and manifold go in completely opposite directions. Now that you're under hard accelleratoin the engine is under a pretty good load and can't tolerate as much advance. So since the engine is under a heavy load there shouldn't be any manifold vacuum. So the extra advance is taken away from the engine to prevent any detonation.

But on the other hand.. If you have it hooked up to ported as soon as you punch it and are under hard accelleration, instead of no vacuum, ported actually increases vacuum. So now your adding even more advance to an engine that is now under a great amount of stress. Pinging occurs, so our first reaction is to just simply retard the timing. Well now at idle and cruise the engine is running even more retarded to compensate for the extra vacuum advance that is being added at full throttle.

So really with full throttle heavy load conditions your timing should be set up to provide the full 36 degrees of advance purely through mechanical. Then the vacuum advance is used on the highway to add advance at cruise to make the engine more fuel effecient and create a better burn in the cylinders since its at a constant speed and can tolerate more advance.
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Old 03-07-2005, 03:49 PM
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Quote:
Originally Posted by Silver_Camaro
But on the other hand.. If you have it hooked up to ported as soon as you punch it and are under hard accelleration, instead of no vacuum, ported actually increases vacuum. So now your adding even more advance to an engine that is now under a great amount of stress. Pinging occurs, so our first reaction is to just simply retard the timing. Well now at idle and cruise the engine is running even more retarded to compensate for the extra vacuum advance that is being added at full throttle.

Ported will see the same manifold pressure (vacuum in other words) under wide open throttle as manifold hookup. Which should be zero vacuum, or close to it under wide open throttle

So really with full throttle heavy load conditions your timing should be set up to provide the full 36 degrees of advance purely through mechanical. Then the vacuum advance is used on the highway to add advance at cruise to make the engine more fuel effecient and create a better burn in the cylinders since its at a constant speed and can tolerate more advance.
Minor detail, ....you want the full 36 degrees of advance purely from your base timing plus the mechanical.

Jmark, What you should notice when you hook the vac advance to a manifold source is your idle speed will increase. So you will have a bit of adjustment to do. It would also be a good time to check the idle mixture adjustment to fine tune as well. The engine should idle a bit smoother under this tune. If you currently are running ported all other operating conditions of the vac advance are the same. Once you tip in the throttle the vac can sees vacuum and dials in the advance. If your not running any vac advance then you should have better throttle response and get better fuel mileage on the hwy.
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  #22 (permalink)  
Old 03-07-2005, 04:04 PM
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Well, I think my sons adjustable light is still here so I'll go give it a try. I'll double check the mechanical and total again. I redid it a week ago when I noticed my weights had gone stuck AGAIN fully advanced. Getting tired of pulling the dist and tearing it down and cleaning the shaft!
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  #23 (permalink)  
Old 03-07-2005, 05:57 PM
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WAY over my head, shewwww

Ok, a little help here...

This article completely hypnotized me.. And what i got outta it was, dont buy that new Pertronix Flamethrower that was recommended in the 383 stroker article ive followed for my build?
And i should go and buy the distributor w/points and use the vac. control can you suggested?

I dont mean to sound ignorant, LOL but i am at this point, but im reading...
I need a little clarification... in a more layman's term...PLEASE..

thanks DJ
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  #24 (permalink)  
Old 03-07-2005, 07:26 PM
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Quote:
Originally Posted by Jmark
Well, as one who has ALWAYS pushed for "Ported vacuum" advances, i'll bite and say I've seen the light. Guess I'll go take the plug off my advance and try manifold and see how it goes.

Since everyone seems to now be on the same page here, i'll ask a question.
My truck is a 1/2 ton chevy, .030 350. 9.2 comp, cam is a Crane 276 ( I think). Headers, Q-jet, mild head work on my 882's with automatic tranny.

I run about 10 to 12 degrees initial timing, plus my weights push the timing to 35 full in by 2600rpm. My normal cruise speed in town is about 2100 and freeway is 2700@65mph. So....according to the article, I can use another 10+ degrees of vacuum advance at idle? My truck idles fine and does not overheat at all. Is this extra 10+ degrees really necessary in my case? Or is it overkill? I guess the plus side is more timing at cruise speed hopefully giving me a little better mileage. My biggest problem is actually hearing the pinging. I never do anymore since my hearing has gone south. Guess I'll have to take my son along for the testing.

Feedback welcome!!

Mark

The real meat of the entire thread is that regardless of what means you use to provide spark lead to your engine, your engine is going to like a specific amount of timing under specific operating conditions (for ideal combustion burn). This is going to be a trial and error process for each individual vehicle, but with the information available, one should be able to design something that is close to ideal, and could be fine tuned to perfect the entire curve.

This thread by Rick W is pretty much how I've always done it myself, and it's not a difficult process to comprehend.

In this day and age of EFI and DIS, it's not that common anymore to find mechanics that can tune older carbureted, distributor type engines.

I've seen tons of fresh tune-ups that ran like crap. Many of them run poorly because somewhere in the fray, the engine's spark advance was plumbed into ported vacuum. The difference between the two in my experience has been night and day, and I have ALWAYS used manifold vacuum, even when the if the factory used ported. The sound of an engine's "sweet spot" is readily evident when you get it right. Anybody can tailor their own custom curve if they've got an advance timing light or timing tape properly installed, and a vacuum guage. No black magic involved at all.
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Old 03-07-2005, 07:44 PM
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Quote:
Originally Posted by 57NAPCO
Ok, a little help here...

This article completely hypnotized me.. And what i got outta it was, dont buy that new Pertronix Flamethrower that was recommended in the 383 stroker article ive followed for my build?
And i should go and buy the distributor w/points and use the vac. control can you suggested?

I dont mean to sound ignorant, LOL but i am at this point, but im reading...
I need a little clarification... in a more layman's term...PLEASE..

thanks DJ
Kinda like when the wife goes on and on and on and.....anyway I digress.

Although I don't use Pertronix that is the type of distributor (electronic) you'd want to use. You would not want a points type.
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  #26 (permalink)  
Old 03-07-2005, 08:06 PM
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Let me ask something here. You know the so called old red neck way of moving the spark plug wires one over in either direction on the terminals. How much timing does that acount for. Would it be kinda like moving a dis. one tooth or two? I mean I know you then have to turn the dis. to get your mech. adv. but as far as int. goes if you move the dis. how much does that effect timing? SOmething I have been wondering.
Thanks

Chris
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Old 03-07-2005, 08:25 PM
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Yes moving the wires on the terminals would be like stabbing in the distributor one tooth off.
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  #28 (permalink)  
Old 03-07-2005, 08:35 PM
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Ok, thanks for the clarification...just need a little directional shove...and as far as the wife, LMAO.... WELL....she's LONG GONE ...
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  #29 (permalink)  
Old 03-07-2005, 08:38 PM
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Thanks Rick. I know someone around here had said something about that and it got me thinking. I just wanted to know what it did. Again thanks great post by the way very useful.

Chris
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Old 03-07-2005, 09:03 PM
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Originally Posted by 57NAPCO
WELL....she's LONG GONE ...
I could use some tips on how to accomplish that, cheaply.
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