Low Compression/High Boost and Pump Gas

I am of the opinion that each engine is different as to what is doable. Two engines that appear to be the same will accept different amounts of boost. I can only relate what has worked well for me. I built my 340 eleven years ago and this spring was the first time I had any problems. I pushed out a head gasket but no other damage. This is what I have. 1968 340 bored .030 over. Stock crank, TRW pistons with a static compression of 8.2 to 1. Eagle H-beam rods. The "X" heads have been very heavily ported and I run a custom cam from Steve Morris Racing. The intake is an Indy Mod man that I had to massage a little to get to work. My head gasket is a Fel-Pro 1006 that has a .039 compressed thickness. I run a Dyers 6-71 roots blower at 9 lbs of boost. My timing is locked at 31 degrees. Now back to my first sentence, I have been told by more than a few so called experts that I can't run that boost and timing without destroying the pistons with pre ignition. After 11 years of running this combo my pistons looked pretty darn good when I replaced the head gaskets this spring. I started with 6-7 lbs of boost and my timing at 28 degrees and started to sneak up on it a little at a time by adding boost and timing in small increments. As I said I ended up at 9 lbs of boost and 31 degrees of timing and thats where the engine seems the happiest. On a side note I did up the boost to 12 lbs a few years back and although it was fun while it lasted I did break my harmonic balancer which took out my timing cover. My guess is that the added pressure from trying to turn the blower faster was to much for the stock balancer.

Just my 2 cents from personal experience. And I run 91 octane.

Jack