TIMING SETTINGS

[Corzette]

Guys, I have a 350 with headers and Holley 600 and a mild CAM. What timing should I use at 800 RPM idle? also, what should my IDLE RPM be? Any help is appreciated.

 

CorZette

[John Scott]

CorZette: A mild cam, hotter than stock, can use a more agressive timing curve. Timing is never going to be the same for different engines. Without a run to a dyno or track, its going to be a trial and error approach. I'd shoot for about 12-16 initial (with the vacuum advance, if you're running it, disconnected when checking). If your balancer wheel isn't degreed up to 40 or so you'll have trouble getting the full advance #s down. Try raising the timing in 2 degree increments until you JUST notice detonation on the top end. DONT RUN IT THERE OR YOU'LL TRASH YOUR RINGS, PISTONS etc. Then back it of a couple. If you have access to a track, continue backing it off until performance decreases. You don't always make more power at the edge of detonation. (blower motors, for example, make more right at the edge, but its a risky game) With more initial advace its easier to adjust your idle/ and mixture circuit on the carb, too. Ideally you want to set your initial advance to an optimum level, good strong low end, not too hard to crank, AND your total mechan. advance usually in by 3000- 3500rpm. Put in more initial, sometimes you have to take out the total on the other end to keep it from pinging. Chevs. with around 9:1 comp. ratio like about 16 initial and 20-22 (read at the crank) more mechanical for a total of about 38 degrees. These are ball park figures. so try what seems to work. Listen carefully for detonation! Since stock distributers usually have too much advance built into them, get one of the spring/weight/limiter kits. Most come with fair instructions. Mallorys have set screws in the distrib. plate. My car idles great @ 700 rpm in gear due to my wide lobe sep. angle on my cam. In contrast my last big block was still sputtering @ nearly 2000 rpm in gear, and wouldn't really smooth out 'till 4000! 7-800 should be ok for a mild cam.

JS

 

[This message has been edited by John Scott (edited May 05, 2000).]

 

[This message has been edited by John Scott (edited May 06, 2000).]

[SpeedRacer]

Really hard to say on the idle because of so many different factors but most of all the cam. With the mild cam you should be close at ~750-800 RPM but again, hard to tell.

 

Most small block Chevy's like around 15 degrees advance at idle without the vacuum advance conected (if you have one). If you have a vacuum advance it should be hooked up to ported vacuum and not direct manifold vacuum.

 

Also, you should check full advance but again do this with the vacuum advance dis-connected. Full mechanical advance should not exceed 43 degrees to be safe. Most of the time an SBC can handle this but if it pings or knocks than back it down a few. This is important because pre-ignition caused by to much timing advance can destroy an engine.

 

At light loads the vacumm advance usually takes it up around 50 degrees for better fuel mileage.