what Lars said. Your setup is very similar to mine...same cam, headers, and duals. Except 670 SA carb, EPS intake, Mallory HEI and 9.7:1CR. I took Lars advice and am a happy camper.
Timing Curve Recommendations?
Thread Starter
Cruising
Joined: Jan 2008
Posts: 12
Likes: 0
From: Lake Charles LA
Timing Curve Recommendations?
I have a 76 Vette with original 350 (but with flat top pistons for a bit closer to 9:1 CR), XE 262, Perf RPM, 750DP, Headers, Duals, 3.08 gears...not a super hot setup, good cruiser. Stock HEI.
I am very familiar with Pontiacs........but Chevy performance specs are new to me.
Anyhow, the initial timing is currently 15-16 (seem to be what it likes). running up the rpms to 2500-3000 and it quickly approaches 40. Seems like alot of timing to me (relative to my Pontiac 400).
Wondering what timing curve (total timing, and timing from vac adv, mech advance) people are using with setups similar to mine. Wondering if I need to upgrade my distributor to an adjustable vacuum advance and/or fool with the mechanical advance.
Thanks for the advice
I am very familiar with Pontiacs........but Chevy performance specs are new to me.
Anyhow, the initial timing is currently 15-16 (seem to be what it likes). running up the rpms to 2500-3000 and it quickly approaches 40. Seems like alot of timing to me (relative to my Pontiac 400).
Wondering what timing curve (total timing, and timing from vac adv, mech advance) people are using with setups similar to mine. Wondering if I need to upgrade my distributor to an adjustable vacuum advance and/or fool with the mechanical advance.
Thanks for the advice
Drifting
Joined: May 2003
Posts: 1,634
Likes: 2
From: Melbourne, Victoria, Australia, the World
Search the forum for LARS and DISTRIBUTOR
You will find Lar's distributor set up papers which will tell you how to make the most of the stock distributors.
Lars is god when it comes to Qjet and Ignition.
Start with 36 deg all in by 3000, no vac, then add full vac to check you have no more than 52 all in. If this is all good, and it idles well, leave well enough alone. Chevies like a bit of advance at idle.
You will find Lar's distributor set up papers which will tell you how to make the most of the stock distributors.
Lars is god when it comes to Qjet and Ignition.
Start with 36 deg all in by 3000, no vac, then add full vac to check you have no more than 52 all in. If this is all good, and it idles well, leave well enough alone. Chevies like a bit of advance at idle.
Tech Contributor
Joined: Aug 1999
Posts: 14,356
Likes: 6,332
From: At my Bar drinking and wrenching in Lafayette Colorado
The Chevy timing curve is identical to the Pontiac - I used to be a dealer for Ken Crocie and H-O Racing working with the Pontiacs...
Run 36 degrees total timing and bring it in as fast as the engine can take it without detonation - just like the Pontiacs. This will usually be in the 2800-rpm range for the 36 total. What the engine wants for initial will depend on the cam being used, but something in the mid-teens is pretty safe. The bigger the cam, the more initial you want (I'm running a 463 Pontiac with 24 initial), but you want to limit total to 36. You might be able to run more than 36 total without detonation, but the torque curve is dropping off once you get over 36 total. Best power will be 34 to 36 in almost all cases (except with fast-burn heads). Limit your vacuum advance to no more than 16, and run it off manifold vacuum.
Run 36 degrees total timing and bring it in as fast as the engine can take it without detonation - just like the Pontiacs. This will usually be in the 2800-rpm range for the 36 total. What the engine wants for initial will depend on the cam being used, but something in the mid-teens is pretty safe. The bigger the cam, the more initial you want (I'm running a 463 Pontiac with 24 initial), but you want to limit total to 36. You might be able to run more than 36 total without detonation, but the torque curve is dropping off once you get over 36 total. Best power will be 34 to 36 in almost all cases (except with fast-burn heads). Limit your vacuum advance to no more than 16, and run it off manifold vacuum.
Le Mans Master
Joined: Jun 2005
Posts: 5,447
Likes: 3
From: Syracuse NY
The Chevy timing curve is identical to the Pontiac - I used to be a dealer for Ken Crocie and H-O Racing working with the Pontiacs...
Run 36 degrees total timing and bring it in as fast as the engine can take it without detonation - just like the Pontiacs. This will usually be in the 2800-rpm range for the 36 total. What the engine wants for initial will depend on the cam being used, but something in the mid-teens is pretty safe. The bigger the cam, the more initial you want (I'm running a 463 Pontiac with 24 initial), but you want to limit total to 36. You might be able to run more than 36 total without detonation, but the torque curve is dropping off once you get over 36 total. Best power will be 34 to 36 in almost all cases (except with fast-burn heads). Limit your vacuum advance to no more than 16, and run it off manifold vacuum.
Run 36 degrees total timing and bring it in as fast as the engine can take it without detonation - just like the Pontiacs. This will usually be in the 2800-rpm range for the 36 total. What the engine wants for initial will depend on the cam being used, but something in the mid-teens is pretty safe. The bigger the cam, the more initial you want (I'm running a 463 Pontiac with 24 initial), but you want to limit total to 36. You might be able to run more than 36 total without detonation, but the torque curve is dropping off once you get over 36 total. Best power will be 34 to 36 in almost all cases (except with fast-burn heads). Limit your vacuum advance to no more than 16, and run it off manifold vacuum.
I've got a ZZ430 clone, fastburn heads, hotcam. 1:6 rollers per GMPP specs.
I keep seeing you say " except with the fast-burn heads", what should I be shooting for?
I apologize to the OP for the high-jack.
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Tech Contributor
Joined: Aug 1999
Posts: 14,356
Likes: 6,332
From: At my Bar drinking and wrenching in Lafayette Colorado
Le Mans Master
Joined: Jun 2005
Posts: 5,447
Likes: 3
From: Syracuse NY
Should I set the initial timing in the mid-teens like you suggested for the others?
The motor came with the heads installed (Fastburn 385), I didn't even get anything from GMPP with the cam specs when I bought the cam.
I really appreciate the help.
Rick
