When the PI was attacked a P-40E pilot jumped in his airplane and shoved the throttle as far it would go and tried to build up some altitude and airspeed. Then he was shocked to see the manifold pressure was only something like 10 inches. Figuring his engine was failing, he despaired, but then gradually realized the gauge had gone all the way past 60 inches and started another circuit. Allison got V-1710's up above 80 in MP on the test stand, the limiting factor not being the engine but the bolts that held it to the test stand.