Timing Question
Thread Starter
Melting Slicks
Joined: May 2006
Posts: 2,590
Likes: 403
From: Nashville TN
St. Jude Donor '09
Timing Question
I set my timing according to Lars and John Hinckleys white papers -- I have 36* all in before 2800 RPMs, but that leaves my initial at 25-26*. Car starts fine, idles fine and has good off-idle throttle response with no pinging. The 25-26* initial just seemed higher than I was expecting. Also, is 10-11* of centrifical good or do I need a broader range? I've read that I can change the bushing to adjust the range but was more curious what the impact was with the way it is currently setup.
My distributor is GM HEI upgraded with Pertronix FlameThrower coil, electronics and weights/springs kit.
My distributor is GM HEI upgraded with Pertronix FlameThrower coil, electronics and weights/springs kit.
Tech Contributor
Joined: Aug 1999
Posts: 14,370
Likes: 6,364
From: At my Bar drinking and wrenching in Lafayette Colorado
A 10-degree advance curve is certainly a little short, but can be made to work just fine. If the car has a big cam, the short curve is exactly what you want, but a smaller cam tends to like a little less initial timing.
You might want to install some stiffer springs just as a test - see if the initial timing comes down with stiffer springs installed. If it does, the initial timing is simply a matter of some of the centrifugal timing coming in at your idle rpm. You can then gain some range back by using some springs that brings in the total timing just a tad higher, say 3000-or-so.
If you car runs well with the advanced intial (and most will), I would keep the curve and simply use a vacuum advance with a very short advance range - run a vacuum advance with about 10-12 degrees of advance. This will get you a vary nice setup with excellent throttle response.
Lars
You might want to install some stiffer springs just as a test - see if the initial timing comes down with stiffer springs installed. If it does, the initial timing is simply a matter of some of the centrifugal timing coming in at your idle rpm. You can then gain some range back by using some springs that brings in the total timing just a tad higher, say 3000-or-so.
If you car runs well with the advanced intial (and most will), I would keep the curve and simply use a vacuum advance with a very short advance range - run a vacuum advance with about 10-12 degrees of advance. This will get you a vary nice setup with excellent throttle response.
Lars
Thread Starter
Melting Slicks
Joined: May 2006
Posts: 2,590
Likes: 403
From: Nashville TN
St. Jude Donor '09
Thank you Lars, that is EXACTLY what I needed to know. 
My cam is not that big, but everything seems to be working fine . . . just didn't want to leave anything on the table.
Lunati 60102L Advertised Duration (Int/Exh): 256/262
Duration @ .050 (Int/Exh): 213/219
Gross Valve Lift (Int/Exh): .454/.468 LSA/ICL: 112/108
RPM Range: 1000-5500
My cam is not that big, but everything seems to be working fine . . . just didn't want to leave anything on the table.Lunati 60102L Advertised Duration (Int/Exh): 256/262
Duration @ .050 (Int/Exh): 213/219
Gross Valve Lift (Int/Exh): .454/.468 LSA/ICL: 112/108
RPM Range: 1000-5500
Tech Contributor
Joined: Aug 1999
Posts: 14,370
Likes: 6,364
From: At my Bar drinking and wrenching in Lafayette Colorado
As long as you don't run into low-rpm detonation there is nothing wrong with bringing the timing in quickly. Your car should perform very well as set up - just make sure it doesn't knock if you lug it around.
Lars
Lars
