What are some of you running in terms of cylinder pressures on your aluminum headed 215s or 300s? I have read that anything more than 175 psi was too high for pump gas, but then aluminum heads could go higher due to faster heat disipation. Also read that a longer stroke motor was better at prevention of detonation than a shorter stroke. Quench is a factor here also, and I have no idea what the accepted ideal quench is for one of these motors. My motor will be a 266 cu in 215 with 300 heads. Initial plans for 9.6 static CR must be changed due to the cam which has a .050 opening of 7 degrees ATDC. With a static of 9.3, dynamic calculates at 186 psi. Is that going to grenade the motor?
While asking my motor expert about Jim's 300 spark plug hole question, I asked about the detonation/cranking pressure issue. After mentioning another's statement that 175 was the max on pump gas he said "they dont know what they are talking about!", and thinks 186 would workout given the alum. heads, and long stroke to bore ratio. Still looking for that optimum quench (squish, piston to head clearance) figure. On the Ford Ys the optimum is somewhere between .038 and .040, which requires the piston to be dead even with deck. But it seems like that is too tight for an all aluminum motor. A friend suggested he take me in to meet with a big time race car motor builder he knows and see what info can be had there. Looking forward to it.
0.040" is a generally accepted figure for quench with non-aluminum rods. 185 psi cranking equates to roughly 8.0 DCR which is fine for 93 octane and aluminum heads. Don't use 0.050" numbers for DCR calculations, they are too far away from the actual closing to be accurate. There are DCR calculators around which use advertised (seat) numbers. And it's the intake closing number that you want to use.
