Steve wrote:
But there are more and more small diesels that run just as fast as
gasoline engines. There's no fundamental limit thats any different than
a gasoline engine, really, but up until now there's not been a demand
for high-RPM diesels.

When I was reading about the Volkswagen TDI engine, I vaguely remember
coming across someone who said that the redline of that engine was set
by the speed which which the burning fuel expanded.

Sounds rather fundamental to me - but, then again, I'm a computer guy.

-Luke