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  #61  
Old Oct 29th, 11, 02:08 PM
olschl69 olschl69 is offline

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Default Re: Timing & Vacuum Advance 101

I just recently purchase an original 69 camaro ss with 396/375 hp. The engine still has the points system. I was debating on replacing the dist with an GM HEI system. Does the HEI work with a vacuum advance system? The guys at the speed shop is pushing the MSD "Ready to Run" distributor w/extenal coil. When I replace the dist, I will also go to a 759 dbl pumper carb (mech secondaries). The car is basically will be street driven on weekends, occassionally running through the gears. Your thoughts and advice?????
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  #62  
Old Oct 29th, 11, 02:15 PM
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Default Re: Timing & Vacuum Advance 101

Quote:
Originally Posted by olschl69 View Post
I just recently purchase an original 69 camaro ss with 396/375 hp. The engine still has the points system. I was debating on replacing the dist with an GM HEI system. Does the HEI work with a vacuum advance system? The guys at the speed shop is pushing the MSD "Ready to Run" distributor w/extenal coil. When I replace the dist, I will also go to a 759 dbl pumper carb (mech secondaries). The car is basically will be street driven on weekends, occassionally running through the gears. Your thoughts and advice?????
Leave it alone, run the factory points dist! What's the point in having an orig engine car that is not kept original! You asked... Of course I'll be the first to say it's yours so do as you wish with it!
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  #63  
Old Oct 29th, 11, 02:54 PM
olschl69 olschl69 is offline

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Default Re: Timing & Vacuum Advance 101

Should I just change the carb, with the 750 dbl pumper w/ mechanical secondaries? I like for the back pumps be activated with the accelerator from the start.
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  #64  
Old Oct 29th, 11, 06:08 PM
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Default Re: Timing & Vacuum Advance 101

Quote:
Originally Posted by olschl69 View Post
I like for the back pumps be activated with the accelerator from the start.
Why? The 396/375 is a bad a$$ combo when tuned properly and the factory gave you everything you need short of a performance tune-up. Think about headers before a carb unless your carb is actually needing to be replaced.
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  #65  
Old Jan 16th, 12, 06:34 PM
bigblockragtop bigblockragtop is offline
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Default Re: Timing & Vacuum Advance 101

Ok here goes I do not have a vacuum advance that is the way my car came It is a street car but not a mild one. I can not afford a distributor right now but not so sure I have to get one. Here is why, I have an ignition control box I am locked out at 40 degrees the box kicks timing back so starting is not an issue(starts right up no kick back every time even hot. The motor is a 496 with a procharger so the compression is low 8-1 since it has the low compression and blower cam it helps with the starting. My question is do I really need to get a vacuum advance since I am able to run locked so advanced already with no problems? BTW the ignition box kicks the timing back 1 degree per lb of boost, afrs are 13-14 while cruising and 11-11.5 wot Thanks
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  #66  
Old Apr 16th, 12, 07:10 PM
armstrong6 armstrong6 is offline
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Default Re: Timing & Vacuum Advance 101

ok I am running a 350HO with a 650DP on it. I have always had a rough idle and a stumble off idle if I goosed it a little to fast. I thought this was just how the carb was and have lived with it. Holley has a "ported vacuum" line that I had the vacuum advance hooked to. I changed it over to the full manifold vacuum, and man what a difference! I gained 3" of manifold at idle. It now idles smooth as glass. I was able to lean it out to where it does not stink like raw fuel all the time too. Thanks for the article, definetly helped me out.
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  #67  
Old May 19th, 12, 08:30 AM
Zman Zman is offline
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Default Re: Timing & Vacuum Advance 101

Quote:
Originally Posted by armstrong6 View Post
ok I am running a 350HO with a 650DP on it. I have always had a rough idle and a stumble off idle if I goosed it a little to fast. I thought this was just how the carb was and have lived with it. Holley has a "ported vacuum" line that I had the vacuum advance hooked to. I changed it over to the full manifold vacuum, and man what a difference! I gained 3" of manifold at idle. It now idles smooth as glass. I was able to lean it out to where it does not stink like raw fuel all the time too. Thanks for the article, definetly helped me out.
I have to ask a stupid question but could you be specific on where the two vacuum lines are exactly located, I hear the terms ported and manifold and think I know the difference, but just want to verify. My understanding is manifold vacuum is at the base of the carb and ported is up by the air screw on the metering block.
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  #68  
Old May 19th, 12, 09:17 AM
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Default Re: Timing & Vacuum Advance 101

It's not a stupid question.

The port for full manifold vacuum is located "below the throttle plate".

Check Figure 6 in this document.
http://www.holley.com/data/Products/...9934-3rev2.pdf
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Last edited by bcm66; May 19th, 12 at 09:31 AM.
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  #69  
Old May 19th, 12, 02:21 PM
Steptoe Steptoe is offline
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Default Re: Timing & Vacuum Advance 101

Manifold has vaccuum all the time...except WOT when drops to 1.5"
Vaccuum is taken below the butterflies
Ported only has vaccuum when the butterflies move off idle
Vaccuum is taken from above butterfies
If u have significant vaccuum with butterflies at idle...the carb has not been set up right.
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  #70  
Old Jan 21st, 13, 07:56 AM
keithl1967 keithl1967 is offline
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Default Re: Timing & Vacuum Advance 101

quick question (hopefully)...The cam I am looking at for a new build makes 9" of vaccum at 800 rpm idle...I assume the B28 (1810) VA can is the way to go?
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  #71  
Old Jan 21st, 13, 09:12 AM
JohnZ JohnZ is offline
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Default Re: Timing & Vacuum Advance 101

Quote:
Originally Posted by keithl1967 View Post
quick question (hopefully)...The cam I am looking at for a new build makes 9" of vaccum at 800 rpm idle...I assume the B28 (1810) VA can is the way to go?
That's correct. Here are the current numbers for the "B28" vacuum advance unit, depending on which source stocks them (ALL vacuum advance units are made by Standard Products, and are re-boxed by the various suppliers):

GM #88924985
AC-Delco #D1312C
Airtex #4V1053
BWD #V329
Standard #VC-177
Wells #DV-1810
Niehoff #DR-305

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  #72  
Old Apr 25th, 13, 09:03 AM
jrb70454 jrb70454 is offline
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Default Re: Timing & Vacuum Advance 101

I'm taking the plunge here too- a new MSD 8361 and a B28 can are due tomorrow! I can't wait to get into this!!

I'm sure I'll tweak until it is right, but I'm looking for a starting point. Should I set the curve and total on the new distributor the same as the non-VA distributor in the car now? I'm assuming I'll be leaning out the idle mixture too. Actually, does anyone have a step-by-step process they use?

Thanks!
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  #73  
Old Apr 25th, 13, 02:14 PM
Steptoe Steptoe is offline
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Default Re: Timing & Vacuum Advance 101

Yes a current thread now
http://www.camaros.net/forums/showthread.php?t=218611
And making use of the search function above u will come across many threads , even talking people thru , stage by stage over couple weeks of dialing an engines mixtures and timing in.
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  #74  
Old May 11th, 13, 06:21 PM
jrb70454 jrb70454 is offline
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Default Re: Timing & Vacuum Advance 101

Is there a total with the VA to shoot for? I have seen 52 "all in"- cruise idle. I have a B28 that was advancing the total to 62 (on top of the 37 mechanical total). The B28 advances 25?, or am I looking at something wrong? The motor was surging going down the highway, so I put a mechanical stop in to limit the advance. The stop eliminated the surge, but is there an optimal VA advance to shoot for?
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  #75  
Old May 12th, 13, 01:34 PM
Steptoe Steptoe is offline
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Default Re: Timing & Vacuum Advance 101

If dialing in an engine without knock sensors..
1/ u need the AFRs idle/ cruise around the low to mid 15s and WOT mid 11s to low 12s.
2/ do not exceed 40/42 degs idle +cent+ VA
3/keep intial as low as possible 8 to around 12.
4/ if a non EGR engine use manifold vaccuum, all in at no more than 1" above idle... MUST be all in at idle speed... ie idle = VA + intial. most mild to mid street engines require between 12 to 18 degs idle depending on cam.
5/The total (WOT) intial+cent will be between 32 degs and 36 degs all in around the to 3000 to 3200 rpms

How to change/ juggle cent advance degs and rate of advance, VA advance degs and ranges to meet the specs your engine requires is covered in links above and search function above.
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