Maybe I wasn't clear. If everything was perfect, the best you could get is 14.7psi atmo pressure at sea level x 8.9:1 compression ratio, which equals about 131psi. The piston rings have a gap, so air leaks past the rings. The slow rotation speed means there is a longer time for the leak to leak, so it's relatively bigger. Thus, at the low cranking speed of 250rpms, you won't see 131psi of compression. Replace the cast iron piston rings with the gap with rubber orings and you might see 130ish, but once the engine fires, it gets a little toasty for rubber orings. Volumetric efficiency is not great at cranking speeds, either, and the throttle may be partially closed, so the engine is pulling against less that 14.7psi in the manifold. There are places in the rpm range where the measured pressure would be above 131, because the ram effect built into the intake (the long runners) sets up a helmholtz resonance which has a pressure wave hitting the back of the intake valve just as it opensm and the measured intake mani pressure will be much higher, say 18psi.