[Excaliber]

It has actually has more to do with the stroke than the piston size. Those really large diesels have a really long stroke and a smaller piston size.

High rpm is much easier to achieve with a short stroke. Classic drag racing "formula", short stroke BIG bore builds rpm faster and revs higher than vice versa. Porsche is famous for short stroke big piston engines. The down side of short stroke? You loose torgue, which is the "leverage" effect you get from a longer stroke/rod combination.

Torque falls off with high rpm, but horse power increases! H.P. is a measure of "time to distance", torque is more a measure of "pulling power", slow but more "force". A Mack Truck is in no hurry, but can pull a 80,000 pound load up a mountain road with a mere 300 horse power, but might have 700 ft lbs of torque at 1800 rpm!

In a Cobra, your probably in a "hurry", need more horse power!

Ernie