Generally racing 40’s don’t explode until around 40K. Then the bottom end of the rod feeds the bushing material though the rest of the engine and out the exhaust. This can cause the engine to seize and the rotational energy to transfer to the case in a rapid and extremely violent manner.

My prediction for top speed in a terminal dive is 185 mph. This based on the data provided: speed in level flight, speed at a 45 degree dive, and 6 pound flying weight.