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I'm trying to set the distributor initial timing for my SBC. It has a mid-range Crane cam with cam timing @.050 of 228 degrees duration intake and 234 degrees exhaust. Do these cams need more advance timing than stock cams? Crane Cams went out of business a few years ago so factory tech won't help. This is my first SBC so I hope you Hot Rodders can suggest a good starting point.

Thanks
Dan

You'll need to advance the initial timing about 10 degrees above stock, BUT, the centrifugal advance needs to be reduced by the same amount. With the vacuum advance disconnected and the line plugged, shoot for 37 degrees total advance at 2500-3000 RPM. It's usually necessary to have somebody recurve the centrifugal advance in the distributor to get those nunbers. Simply increasing the initial advance will result in too much total spark advance, and overheating and/or piston damage.
Jerry

Hotrod Lincoln:
That sounds like a good plan. I have an ACCEL performance distributor which came with a re-curve kit. I'll read the mfr.'s instructions for that.

Thanks
Dan

Does your distributor have a vacuum advance? Most Hi-po distributors don't have, which will cost you a little MPG at highway cruise. If not, go for 37 degrees total advance at speed. At light-throttle cruise, most small block engines will handle 45 degrees or a little more of total advance, which goes back to 37 as soon as the throttle is opened up to accelerate.
Jerry

Not questioning your expertise Jerry, but isn't 45 degrees exactly one cylinder in the firing order? Wouldn't that mean that the piston is already half way back down at detonation? I don't follow the idea that that could create very much power.

V8 engines fire every 90 degrees. It would take a 16-cylinder to get a cylinder firing at the 45-degree point. The ability to handle very early iginition timing is a factor of engine load, as well as speed. The idea is to have the flame front from the burning fuel meet the piston crown just as the piston rocks over TDC, and get the maximum amount of time to push the piston down the bore. As speed increases, the piston's dwell time at the top of the stroke is very short, and the flame front travels across the combustion chamber at almost a constant speed, regardless of RPM. Based on hundreds of dyno runs I've done on small block race engines, 36 to 37 degrees of timing advance is where these engines run best at full load, 2 inches of manifold vacuum or less.

As the vacuum increases, (light throttle) the timing can be advanced another 8 to 10 degrees for fuel economy reasons, as long as the timing is retarded again as soon as the throttle is opened and vacuum drops during acceleration, passing, pulling uphill, etc. A vacuum advance unit does this on older engines, or electronic timing advance accomplishes the same result on computerized engines. I've seen timing advance of up to 55 degrees on light-throttle coast conditions on a scan tool during road tests.
Jerry

Edit: The timing advance makes the plug fire before top dead center, not after. The plug fires, and starts the fuel burning BEFORE the piston reaches the top, not after. As speed increases, the plug must fire sooner, to get the flame and the piston together at the right time.
Jerry

Ah, I see said the blind man. I forgot to account for the piston making two cycles per revolution. I'm gonna try advancing my timing some more and see if the T'Mater will run a little better. I gots me one o' them crane cams too, although not quite as radical as Dan B.

I used to drag race at NDRA (defunct now) like ANRA, they used to run the March meet in bakersfield, i had a 70 camaro, 327 w/11.5 compression pistons, hogged out 2.02 cylinder heads, 750 carb and hooker super comp headers. I had timing tape around the vibration damper and I always ran 45 degrees of timing. I messed around with it but it always liked it there.. I ran 15's until i swapped out the heads with 76cc stock heads that had a mild porting, dropped to 14.6 ... there is something to be said about velocity. Timing is tied to cam and compression and is individual as the engine. Best thing is to use a timing degree wheel, that should tell you a lot.

Back in the mid-1950's one of the sponsors of the family race car was a trucking company that had a chassis dyno in their maintenance shop. Dad did a lot of race tuning on that old '34 Ford coupe with the alcohol-fueled flathead V8 on that dyno. Once they solved the wheelspin problem by building a ramp onto the rear bumper and pulling a road tractor partway up it to load down the racecar rear wheels, they started tinkering with ignition timing and carburetor mixture.

Once the fuel mix was sorted out, the ignition timing would be advanced one degree at a time with the engine running at full throttle until the horsepower maxed out, then the timing would be advanced one more degree, and the power loss recorded. Back to max power, and start retarding the timing. It was necessary to retard the timing 5 DEGREES to lose as much power as just one degree of over-advance would drop!

When in doubt, DO NOT over-advance ignition timing!
Jerry