By keeping timing out of the cylinders at high load/low rpm, the motor stayed out of detonation and made power across the entire rpm curve. The key to running a 10:1 compression ratio with iron heads lies within the spark curve, which is why we used a box-stock Pertronix distributor set-up with a rather slow advance. With our camshaft specs, the motor was set up to pull 14 inches of vacuum at 800 rpm while running 36 degrees of total advanced timing. When combined with the 0.040-inch-thick head gasket and 64cc to 67cc combustion chambers, the compression ratio would range from 9.7:1 to 10:1. All tests would be on 91-octane pump gasoline, which is why our Hye-Tech mule motor had its valve-relieved Speed-Pro pistons sitting 0.010-inch in the hole. To even the testing ground for all of the heads, intake runners of 185 cc's-or-smaller would ensure every head was a true street contender and offer consistent torque at all engine speeds.
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