Timing
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 750
Likes: 82
From: Bedford IN
Timing
I recently rebuilt the motor in my 1976 vette L-48. I believe i raised the compression to about 10 to 1. I put a 270 dur xtreme energy comp cam in it. i have had to take the timing clear up to and 24 degrees advanced. Does this seem right? sure does run good when i do it though, haha.
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 750
Likes: 82
From: Bedford IN
Well i didnt have to disconnect it, i was told to put the vacuum advance on the side that has no vacuum at idle so when i am timing it doesnt change if you take it off or not. is this right? i thought that it should be on the vacuum at idle side.
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
Originally Posted by speedsk899
I recently rebuilt the motor in my 1976 vette L-48. I believe i raised the compression to about 10 to 1. I put a 270 dur xtreme energy comp cam in it. i have had to take the timing clear up to and 24 degrees advanced. Does this seem right? sure does run good when i do it though, haha.
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 750
Likes: 82
From: Bedford IN
When would i read the total timing? I dont remove the vacuum advance hose because it doesnt make a differnece. do i need to change the hose so that i have vacuum to the vacuum advance at idle?
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Instructor
Joined: Mar 2006
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From: Cumming GA
speedsk99........ There are lots of opinions on how to set up your timing, but, at the end-of-the-story it always is what your total advance becomes at lets say 3000rpm. That should be between 34-36max.
What will happen is if you start with too high of an advance, when you distributor "adds" to it and you hit over that 34-36 mark, you will start to knock and it will run like crap at top-end. Car no-doubt will run great at bottom end with what seems like quick response. (plus may run hotter). Same with how it sounds. When you advance it at idle it always sounds better with more advance.
Best way to check it is if you can get a hold of a timing light with an advance function.
What distributor are you using? (weights, spring combinations, and some even have bushings on the weight posts that all come into play)
BobR
What will happen is if you start with too high of an advance, when you distributor "adds" to it and you hit over that 34-36 mark, you will start to knock and it will run like crap at top-end. Car no-doubt will run great at bottom end with what seems like quick response. (plus may run hotter). Same with how it sounds. When you advance it at idle it always sounds better with more advance.
Best way to check it is if you can get a hold of a timing light with an advance function.
What distributor are you using? (weights, spring combinations, and some even have bushings on the weight posts that all come into play)
BobR
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 750
Likes: 82
From: Bedford IN
I have an HEI dist with weights and springs. I set the timing up the take the car out and run it wide open throttle to make sure it doesnt spark knock. It runs great through all the RPMS. It just seems wierd that i have to advance it so far. To 0 mark on the balancer is all the way at the top at idle. Am i crazy or does this sound correct?
Tech Contributor
Joined: Aug 1999
Posts: 14,384
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From: At my Bar drinking and wrenching in Lafayette Colorado
Sound normal. Initial timing around 18-24 with total timing (without vac advance) limited to 36 is where you want it to be for a performance cam.
Safety Car
Joined: Jun 2004
Posts: 4,652
Likes: 80
From: Lakeland Florida
Originally Posted by speedsk899
When would i read the total timing? I dont remove the vacuum advance hose because it doesnt make a differnece. do i need to change the hose so that i have vacuum to the vacuum advance at idle?
There may be some confusion here. What I think you are referring to here is setting the timing at approx. 36 degrees. This is with the vac advance hose to the distributor off, and plugged. The 36 degree should come in at approx. 2500 -3000 rpm. To change when you get full timing at 2500rpm the spring weight can be changed ( this is when the color of the springs are referred to as silver, bronze, gold ). After you set the total timing to 36 degrees at 2500-3000 rpm, or whenever it cannot advance anymore, then you can check the inital timing at idle. This may be around 12-16 degrees. This would be your inital curb idle condition. After this you can then reconnect the vacuum advance hose. The vacuum advance unit is what will bring the additional timing in to compensate for the load on the engine under acceleration.
That may explain why you are seeing your timing setting so high. Do you have a digital timing light with the advance feature to see the timing set so high?
kdf
Safety Car
Joined: Jun 2004
Posts: 4,652
Likes: 80
From: Lakeland Florida
Originally Posted by lars
Sound normal. Initial timing around 18-24 with total timing (without vac advance) limited to 36 is where you want it to be for a performance cam.
I was hoping you would add your wisdom to this. For a performance cam it appears you need more initial timing than a stock cam. Would a stock cam still be in the 12-18 degree range.
kdf
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 750
Likes: 82
From: Bedford IN
Ok, I guess my next question would be that, should there be vacuum to the vacuum advance at idle. Mine does not have any. by the way i have an edelbrock 600CFM carb on it. Thanks for all the help already
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
Originally Posted by speedsk899
Ok, I guess my next question would be that, should there be vacuum to the vacuum advance at idle. Mine does not have any. by the way i have an edelbrock 600CFM carb on it. Thanks for all the help already
Ported = no
Manifold = yes
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
Originally Posted by speedsk899
I have it hooked up to the front of the carb. Should i change it?
I think you should get it all set up as is and see how it runs. Once you get it running right, you can then experiment with changing vacuum sources. Both work fine, but some get better results using Manifold vacuum.
