My 1970 Z28 is a numbers matching car with the original LT1-350. It has been completely done over with slight upgrades in cam lift on the intake and exhaust. I have adjusted the floats on the carb and adjusted the vacuum on the carb using the set screws at maximum vac. I am running CAM2 race gas at 110 octane due to the 11:1 compression. Your website calls for total timing at 34-36 degrees and I am at 34 degrees. However, if you let the car idle and gun the gas, it appears to let out some unburnt fuel. It smells rich. The timing is set at about 11 degrees advanced. I am running a Mallory hifire box. I was told that will burn all the fuel in the cylinder yet I am seeing a whitish smoke at times and it smells very much like fuel. What could be the issue? Should I jet down the carb slightly? Oil pressure starts and 70 psi when cold then drifts down to about 25-30 when hot.

Regards in PA

Total timing of 34-36 degrees is not a hard limit, just the point where most Chevy small blocks seem to run best. Each engine is different, and yours may prefer more timing, particularly with the octane you are running. If it is a true 110 octane, I would think it is a little high. There are many cars with static compression ratios of 11:1 doing well on 92-octane pump gas. One of the properties of High octane fuel is that it will burn slower, thus reducing the potential for detonation, but if the burn rate is too slow, such as yours seems to be, there will be unburned gas in the exhaust. Have you tried running premium pump gas to see how it works in your engine? Might be worth a try (and save you some $$$). Good luck.

Will the unburnt gas cause cylinder washout?

Probably. Pull the dipstick and check it to see if you smell gas in the oil.

Total timing of 34-36 degrees is not a hard limit, just the point where most Chevy small blocks seem to run best. Each engine is different, and yours may prefer more timing, particularly with the octane you are running. If it is a true 110 octane, I would think it is a little high. There are many cars with static compression ratios of 11:1 doing well on 92-octane pump gas. One of the properties of High octane fuel is that it will burn slower, thus reducing the potential for detonation, but if the burn rate is too slow, such as yours seems to be, there will be unburned gas in the exhaust. Have you tried running premium pump gas to see how it works in your engine? Might be worth a try (and save you some $$$). Good luck.

I've got a similar setup as the threadstarter's car. '70 Z28 with orig carb, intake, dist, smog, etc......but also have a slightly larger cam, and some valvetrain goodies.

I don't have the cam spec's in front of me right now, but I was playing with the timing some tonight, and ended up at:

1100 rpm curb idle (can't get it to idle much lower)
16* initial advance
14* centrifugal
30* total adavance

Do these number's sound reasonable?

It seem's to run much better now except that I'm on pump gas only, and am getting some valve ping. I usually mix the CAM-2 (110 octane) with premium pump gas, and it work's well to keep the ping down, and the car run's much better. Time to head to the speed shop and refill the jug's $$$$$$$$$$.

30 degrees of total advance seems awfully low. I assume you arrived at that figure by adding the 16* of initial and the 14* of centrifugal. Remember that the advance in the dist runs off the cam, and that the cam runs at twice the speed of the crank, so advance at the crank equates to 2x that of the cam advance. If you did not account for this, you might actually be running 44* of total advance. This might account for your pinging and not being able to get the idle down. If you have or have access to an advance timing light, try to see what the total timing is around 2500-3000 rpm. If you can get the total timing down around 38*, you might find you no longer need to mix the racing gas with premium and that $$$$$$$$$$ goes better in your pocket than it does in the tank. Good luck.

Oops! I must have been half asleep when I wrote the above. I confused the mechanical advance with the vacuum, in which the crankshaft advance is twice that of the camshaft.

Your total advance (initial + mechanical) should still be somewhere around 34-38 degrees, probably closer to 38 than 34 with the engine you are running. You might need to look at the mechanical advance your distributor has now and increase it rather than to try to add enough initial to bring the total up to 38. Sorry for any confusion.