C2 Timing Advance Settings

[Larry S.]

Maybe someone can tell me if the 36 degrees advance (which is approx 12 deg. initial and 24 deg. centrifugal with vac adv. out of the picture) that John Hinckley talks about in his very informative articles, should all be in at between 2500 - 2800 RPM's? Seems I read that somewhere. I am wondering if the 36 deg. should come in sooner if the engine is a SB 327-375 (FI) vs a BB 427-425 engine, or do you set them both up to achieve the 36 deg. basically in the same RPM range?

[Joe C.]

Re: C2 Timing Advance Settings

Should be all in by 2350.

[Paul H.]

Re: C2 Timing Advance Settings

36 degrees all in between 2500-3000 rpm's is how I have always done it, small block or big block. I have even gotten away with 38 degrees but you can get into detonation when you get into that range.

[Duke W.]

Re: C2 Timing Advance Settings

It depends on the engine configuration. C2 OE SB centrifugal curves range from 24 to 30 degrees and are all in at speeds ranging from 2350 to 5100. This is quite a wide range and big blocks cover almost as wide a range.

How quickly the advance can be brought in depends on detonation. Engines with late closing inlet valves can tolerate more advance at low revs.

The OE setup is usually a good place to start and other than the 365/375 HP engines you can try lighter springs to bring in the advance quicker to the limit of detonation. The 365/375 HP centrifugal curves are already very aggressive - all in at 2350 - and don't need to be made quicker. Also, the OE recommended initial timing for these engines is 12 nominal with a range of 10-14.

The 36 total (12 initial plus 24 centrifugal) all in at 3000 or whatever for small blocks is a guideline or decent starting point for most engines with 24 degree distributors.

If you have a 30 degree centrifugal distributor, you should run 6-8 initial and get the full 30 degrees in as quickly as possible without signficant low rev detonation, which is usually the limiting factor in how quickly you can bring in the centrifugal. It's a matter of experimenting with your specific engine, fuel octane, typical air density, etc.

The "36 total" is also a guideline. I say 34-40; 34 if the engine tends to detonate at high revs and up to 40 for peak high rev power, especially if you use high octane fuel like 100LL avgas. Again, it depends on the configuration, fuel octane, and experimentation. Big block best peak power timing might be as high as 42.

If the engine detonates at high revs with 34 degrees or more total, then you need to increase fuel octane or lower the CR.

If the high rev timing for peak power is, say, about 38 degrees, then retarding it 3 degrees will only lose about one percent power, which is barely consistently measurable on a dyno, much less the SOTP, so fretting over one or two degrees timing is ridiculous, and if your distributor isn't shimmed up to two to five thou end play, it's going to have at least that much spark scatter.

Duke

[Larry S.]

Re: C2 Timing Advance Settings

I have experimented with lighter springs in my '66 TI distributor (427-425) and am currently at 36-38 deg. around 2100 RPM. I will have to road test it and watch for detonation.
I also have a '64 327-375 FI car that I am going to review the timing,etc., as it seems "dead" when I stand on it. I know that the FI's are better at higher revs. So should the 327-375FI have all the 36-38 deg. advance in by say 2350 RPM's also ??

[Duke W.]

Re: C2 Timing Advance Settings

You really can't improve on the OE 365/375 HP centrifugal curves. Bringing it all in at 2000 or less won't do any good and could cause detonation assuming it has something close to the original CR.

These engines are notoriously torque-shy due to the 30-30 cam, which is way to big for a sensible road engine. The 375 HP FI engine is worst because it has a single plan manifold.

If you can get the centrifugal all in on a L-72 at 2100 I suspect that somewhere along the line the CR has been lowered. Even with the relatively lazy OE curve, some original L-72s detonate excessively with the OE recommended initial timing and the best available pump gas and either need to have some higher octane fuel added or reduce initial timing a few degrees.

Most OE SBs will operate detonation free on premium unleaded with the OE recommended initial timing and centrifugal curve and many can handle a more aggressive curve.

Duke

[Larry S.]

Re: C2 Timing Advance Settings

Thanks Duke. You are always very helpful and I appreciate it !
Larry