Thread: ? about a bbc running 8 degrees btdc, total 30 degree at 3200 rpms

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have a rebuild(not by me) 1974 454 bbc, which I have just put in a 39 chevy. I don't know the cam, but would say it is a mild cam. I have always been told you want to run total mech. between 32-34 degrees at 3000 rpms,
I have a mallory unilite 9000comp dist., which has 24 degree mech timing built in , no vacum. so the intial should be 10-12 degress btdc, but the engine runs best with 8 degrees intial timing & 30 total. will running with that low of total timing damage the engine? or should I run the intial up to 10? the rearend is running 3.00 gears with 29" tall rear tires. one more question, why doesn't the dist. need a vacum advance for the engine?

Originally Posted by hottrodd57

have a rebuild(not by me) 1974 454 bbc, which I have just put in a 39 chevy. I don't know the cam, but would say it is a mild cam. I have always been told you want to run total mech. between 32-34 degrees at 3200 rpms,
I have a mallory unilite 9000comp dist., which has 24 degree mech timing built in , no vacum. so the intial should be 10-12 degress btdc, but the engine runs best with 8 degrees intial timing & 30 total. will running with that low of total timing damage the engine? or should I run the intial up to 10? the rearend is running 3.00 gears with 29" tall rear tires. one more question, why doesn't the dist. need a vacum advance for the engine?

I would try and have the advance out before 3,000 rpm's.

I'm running 28 total so I can use 91 octane gas. I do have vaccum advance also. Its adjustable and is set for 10 to 15 deg. of advance. I get 13.3 mpg if I behave. BBC 454+.030- 10.7:1 comp -Iron heads- comp 280H cam. 308 HP at wheels on 91 octane

In general vacuum advance helps with mileage, emissions, and starting on street engines. You can run fine without it as long as you have a distributor that you can tune the mechanical advance on.

In general BBC's with no vacuum advance like about 12 deg initial and a fairly aggressive ramp to 34-36 all in by 3000 rpm. I could believe there are those that like 8 deg initial as well. In general w/o vacuum advance you run as much initial as you (and your starter) can tolerate.

Will it hurt anything? I don't think so as long as there is no detonation due to being too far advanced and you have a decent starter. 8 deg initial should be easy on starter.

Kitz

Shouldn't hurt, but you'll be more prone to run hot and fuel efficiency will not be so great without enough timing lead. Unless you have fairly high compression (>10:1) you ought to be able to run 34-36*+ with pump premium no problem, but there's too many variables we don't know such as compression ratio, cam timing, and fuel grade to say for sure.