Question about Distributor Advance - Team Camaro Tech
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post #1 of 51 (permalink) Old Jun 6th, 19, 12:03 AM Thread Starter
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Question about Distributor Advance

The distributor I have in my setup is a Summit Billet Distributor 850050. I actually have it locked out on it's mechanical advance. I have a pretty noticeable bog when I first give it gas on the throttle. It runs really good otherwise. It is still not tuned by a person with knowledge. It was done by me. Below are the curves for the springs that I could install in the distributor. What do you think I should do? I can also get different accelerator pump cams, or jets. I have a Holley 750 DP. By my inexperienced opinion, I still think it's too much air/not enough gas, but timing could be the culprit as well.

By the way, I just LOVE the Fidanza aluminum flywheel. This thing has some amazing throttle response, especially if I can tune out the initial bog.

Thanks!

Brett......




1969 SS 396 X66 - RS Conversion - TKO600 - 3.73 Posi - Paint Code 71-LeMans Blue
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post #2 of 51 (permalink) Old Jun 6th, 19, 12:50 PM
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Rufas
 
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Re: Question about Distributor Advance

Ahs....NO vacuum advance, mechanical locked out, dyno hero's delight, car must be a Top Fueler strip car, not for street. Looks like this really needs a sign.
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post #3 of 51 (permalink) Old Jun 6th, 19, 01:29 PM
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Re: Question about Distributor Advance

Quote:
Originally Posted by Brettallen59 View Post
The distributor I have in my setup is a Summit Billet Distributor 850050. I actually have it locked out on it's mechanical advance. I have a pretty noticeable bog when I first give it gas on the throttle. It runs really good otherwise.

By the way, I just LOVE the Fidanza aluminum flywheel. This thing has some amazing throttle response, especially if I can tune out the initial bog.

]
so you have mechanical advance locked??...meaning Centrifugal advance is locked?

what is your timing advance at idle and at 2500 rpm?

what ignition box you running?

a lighter distributor spring will bring the centrifugal advance in sooner

regarding the light weight FW...yeah it will have quicker rev response but suffer on off the line (aka bog) unless you have the rpm's up or slip the clutch. Inertia from standard weight FW is much better for street/Strip. Lightweight FW are more suited for AutoX
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post #4 of 51 (permalink) Old Jun 6th, 19, 02:05 PM
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Re: Question about Distributor Advance

If mechanical is all you have to adjust in the distributor and limited knowledge of timing curves, Maybe try the timing curve 2, and set you initial timing around 15~18 and try it. tune and adjust from there.

It would work much better if you had a vacuum advance to work with.

dave ray knows his spark, he's just ornery. lol

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post #5 of 51 (permalink) Old Jun 6th, 19, 05:21 PM Thread Starter
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Re: Question about Distributor Advance

So let me re-phrase my verbiage. It's not a "Bog". When my engine is idling, and I give the carb linkage a quick "Pull", it will hesitate, or just not raise rpms immediately. When I am driving it, I have not yet been able to try to accelerate aggressively yet, because I am still breaking in the tranny & clutch. Sorry for the confusion.

Brett.....

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post #6 of 51 (permalink) Old Jun 6th, 19, 05:27 PM
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Re: Question about Distributor Advance

So..... if it's not a secret, how much initial spark advance do you have that doesn't advance at any time ever?

Jon N

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post #7 of 51 (permalink) Old Jun 6th, 19, 05:46 PM Thread Starter
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Re: Question about Distributor Advance

Quote:
Originally Posted by SoCal805 View Post
so you have mechanical advance locked??...meaning Centrifugal advance is locked?

what is your timing advance at idle and at 2500 rpm?

what ignition box you running?

a lighter distributor spring will bring the centrifugal advance in sooner

regarding the light weight FW...yeah it will have quicker rev response but suffer on off the line (aka bog) unless you have the rpm's up or slip the clutch. Inertia from standard weight FW is much better for street/Strip. Lightweight FW are more suited for AutoX

I can definitely put the lighter springs on it. I will put a timing light on it again and verify the timing. It just seems like it is an accelerator pump shot that is either too much but it really seems to me like it's not enough. Once i am off of a dead idle, it ramps up RPM's really nicely, so I think the timing is good. When the engine is at operating temp and I shut it off, there is a small amount of starter drag, so I know I am at the most advance I want to be at. My AFR is at 12 at idle. I still need to watch it while I'm at WOT to see where it is then....

Brett.....


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post #8 of 51 (permalink) Old Jun 6th, 19, 05:53 PM Thread Starter
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Re: Question about Distributor Advance

Quote:
Originally Posted by dyno jonn View Post
So..... if it's not a secret, how much initial spark advance do you have that doesn't advance at any time ever?
It's not a secret..It's an unkown. I don't know. A long time ago when I put the stupid light on it, it read 46. That's kinda why I took the centrifugal out, I didn't want it advancing any more. Now I know that is incorrect, so I kinda gave up using the stupid thing. I am not sure if the timing indicator is just not in the right location, or if the harmonic balancer moved from the rubber insulator that's on it. I have just been going by how well it is running. It is running real good, it's just from a dead idle the second I give it gas, it hesitates, then rpms go after that. I don't know anyone local that can come over and mess with it and tune it. It's really not bad....

Brett.....

1969 SS 396 X66 - RS Conversion - TKO600 - 3.73 Posi - Paint Code 71-LeMans Blue

Last edited by Brettallen59; Jun 6th, 19 at 05:55 PM. Reason: typo
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post #9 of 51 (permalink) Old Jun 6th, 19, 07:29 PM
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Re: Question about Distributor Advance

I'll try to answer the "bog" issue. I believe your Holley 750 comes with a #28 squirter installed in the primary side of this carb and a #31 squirter installed in the secondary side. I used to have the same type of bog/hesitation from a standing start that you are experiencing. I suggest you remove the #28 squirter from the primary side and replace it with a #31 squirter. Do not change the secondary squirter.

If this does not completely solve your issue, you may also need to purchase (and experiment with) a Holley accelorator pump cam assortment kit.
https://www.summitracing.com/parts/hly-20-12

With regards to your timing, I suggest you unlock your centrifugal/mechanical advance in your dizy, purchase a basic timing light, and check your timing specs. If you are not sure if your balancer TDC mark is correctly oriented, purchase a TDC tool that can be inserted thru a spark plug port to confirm. Just do a search on how to correctly use this tool.
Below is a link to a post the discusses timing and finding TDC. Post #17 starts to address finding TDC.
https://www.camaros.net/forums/18-en...questions.html

You may also want to see if your current distributor can accept a vacuum advance canister. For a street car, you really should consider using both mechanical and vacuum advance.

Good luck!
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post #10 of 51 (permalink) Old Jun 7th, 19, 12:10 AM Thread Starter
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Re: Question about Distributor Advance

Quote:
Originally Posted by oldschoolchevy View Post
I'll try to answer the "bog" issue. I believe your Holley 750 comes with a #28 squirter installed in the primary side of this carb and a #31 squirter installed in the secondary side. I used to have the same type of bog/hesitation from a standing start that you are experiencing. I suggest you remove the #28 squirter from the primary side and replace it with a #31 squirter. Do not change the secondary squirter.

If this does not completely solve your issue, you may also need to purchase (and experiment with) a Holley accelorator pump cam assortment kit.
https://www.summitracing.com/parts/hly-20-12

With regards to your timing, I suggest you unlock your centrifugal/mechanical advance in your dizy, purchase a basic timing light, and check your timing specs. If you are not sure if your balancer TDC mark is correctly oriented, purchase a TDC tool that can be inserted thru a spark plug port to confirm. Just do a search on how to correctly use this tool.
Below is a link to a post the discusses timing and finding TDC. Post #17 starts to address finding TDC.
https://www.camaros.net/forums/18-en...questions.html

You may also want to see if your current distributor can accept a vacuum advance canister. For a street car, you really should consider using both mechanical and vacuum advance.

Good luck!
Thank you very much Mike for your suggestions. These are the things that I was hoping to hear from the knowledge base here at TC.
Brett....

1969 SS 396 X66 - RS Conversion - TKO600 - 3.73 Posi - Paint Code 71-LeMans Blue
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post #11 of 51 (permalink) Old Jun 7th, 19, 06:42 AM
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Lynn
 
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Re: Question about Distributor Advance

Brett:

No one can give you much in the way of guidelines without knowing more about your engine.

Cubic Inches (assuming from your sig you are running a big block)
Heads
Camshaft
Static Compression Ratio
what is the engine vac at idle?

Without the above, it would be impossible to give you a good starting point. Even back in 1969, Chevrolet used different different distributor specs for each engine. Even used a different distributor for the same 295 horse 350 depending on if it had manual or auto trans. Manual trans got 1111488 and auto got 1111489. The curve is slightly different.

Most street cars respond better with a vac advance. But, you can still make this one work pretty well. You are giving up some effeciency.

Do you know where you have things set right now? I realize the advance mechanism is locked out. Have you put a timing light on it to see where it is?

Lynn
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post #12 of 51 (permalink) Old Jun 7th, 19, 07:39 AM
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Re: Question about Distributor Advance

Brett,
I know there a lot of people that will say otherwise but personally I don't see how you can run a street engine and not use vacuum advance. If you want to prove it, start the car and bump your base timing up to about 40 degrees. See if your problem goes away. Obviously you cant run the car down the road that way but it will tell you if your lack of vacuum advance is the problem.

An engine always wants to have as much advance as possible without getting into detonation. You simply cannot do this under all rpm and load conditions on a street engine without using a vacuum advance distributor. Simply cannot be done. You might get a compromise that will work ok but it will never be as good as it can be. A locked advance will only be correct at a single rpm and load combination. Nowhere else. If you are racing and are only concerned with WOT then it can work but thats the only time.
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post #13 of 51 (permalink) Old Jun 7th, 19, 08:07 AM
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Re: Question about Distributor Advance

I am running a 540 horse SB with no advance with 38* timing @ 3000. I can idle through slow traffic at 35 mph in 4th gear and get 15 mpg on open road
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post #14 of 51 (permalink) Old Jun 7th, 19, 08:18 AM
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Re: Question about Distributor Advance

Quote:
Originally Posted by flat tire View Post
I am running a 540 horse SB with no advance with 38* timing @ 3000. I can idle through slow traffic at 35 mph in 4th gear and get 15 mpg on open road
That doesn't mean that it would not be even better with the correct amount of advance under all conditions.

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post #15 of 51 (permalink) Old Jun 7th, 19, 08:33 AM
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Re: Question about Distributor Advance

Quote:
Originally Posted by BillK View Post
That doesn't mean that it would not be even better with the correct amount of advance under all conditions.
I am very pleased with throttle response and general running of the engine. if it aint broke don't fix it
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