383 ignition timing help
Thread Starter
Heel & Toe
Joined: Mar 2005
Posts: 15
Likes: 0
383 ignition timing help
I just got my 383 stroker engine built and put into my 77 corvette and i'm wondering exactly where to set my timing at full advance. The engine is a 383, brand new bottom end, speedpro pistons, recon rods, nodular iron crank, moly rings, fully balanced. The top end has world sportsman heads with mild port/polish job, weiand single plane intake, edelbrock 600 cfm carb and has a big cam with solid lifters and roller tip rockers. The compression is 10.7:1. This motor is for street, and has a built turbo 350 transmission. What I am looking for is total advance for 93 octane and for 110 octane, (for occasional track use). I have a timing light with adjustable advance so what numbers should I be running for 93 and for 110 for good performance yet drivable. Thanks in advance. And I'm running vacuum advance, which is adjustable, but should I have it hooked to ported vacuum or manifold vacuum, I hear opinions on both places but what do you guys think?
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Back when I had iron heads and the same compression. I used 14 initial and 24 mech all in at 3200 rpm. I had ping until I started delaying how fast it got total timing. The adjustable vacuum advance I had added about 6 more while in the cruise mode high vacuum on a ported source.
It really depends on the cam. If you set it up like mine and you get ping at WOT retard it a couple of degrees. If your getting rattle going down the freeway at 70 turn down the vacuum advance
It really depends on the cam. If you set it up like mine and you get ping at WOT retard it a couple of degrees. If your getting rattle going down the freeway at 70 turn down the vacuum advance
Last edited by gkull; May 19, 2005 at 09:49 AM.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
How big is your "big" cam. That will have a lot to do with it. If the motor is setup properly you should not have much of a difference from running on the street and track. Try to run it on 93 all the time. No need for more expensive fuel if it is not needed. I agree the 600 carb will be a little small for what you have.
Burning Brakes
Joined: Nov 2003
Posts: 990
Likes: 0
From: North Texas
With the cam in my 383, I set my max timing for 34-35 degrees in by 2500. I could not set it by inital timing. The engine just wouldn't run correctly.
After talking to LARS, the solution was to let the Vacuum advance make up the different. So, I installed the vacuum advance LARS suggested and connected it back up. Once the car actually starts, the vacuum advance kicks in and adds timing to make the car idle.
Now, it idles great and works like a champ.
After talking to LARS, the solution was to let the Vacuum advance make up the different. So, I installed the vacuum advance LARS suggested and connected it back up. Once the car actually starts, the vacuum advance kicks in and adds timing to make the car idle.
Now, it idles great and works like a champ.
Thread Starter
Heel & Toe
Joined: Mar 2005
Posts: 15
Likes: 0
not sure on the specs for the cam but it is made for 3/8 mile dirt track racing, if this helps. I do agree the carb is a little small but I'll change it later when the money comes around. The question i'm still wondering, is should vacuum advance be connected to ported or manifold vacuum?
Team Owner
Joined: Feb 2003
Posts: 30,183
Likes: 313
From: Lake Norman NC
i run 38 degrees total advance...it runs at 36 fine, but feels stronger at 38. I will be getting some dyno times in shortly, and test a few different timing setups to find optimal performance.
Burning Brakes
Joined: Nov 2003
Posts: 990
Likes: 0
From: North Texas
Originally Posted by page454
not sure on the specs for the cam but it is made for 3/8 mile dirt track racing, if this helps. I do agree the carb is a little small but I'll change it later when the money comes around. The question i'm still wondering, is should vacuum advance be connected to ported or manifold vacuum?
I personally use manifold and that's my suggestion to you.
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Melting Slicks
Joined: Apr 1999
Posts: 2,010
Likes: 3
From: Moon Twp. PA USA
Originally Posted by page454
not sure on the specs for the cam but it is made for 3/8 mile dirt track racing, if this helps. I do agree the carb is a little small but I'll change it later when the money comes around. The question i'm still wondering, is should vacuum advance be connected to ported or manifold vacuum?
