Originally Posted by DaveK
Assuming you mean any engine, then you are into the realms of F1 V8 engine @ approx 100 kgs and 800 bhp or the Moto Gp 990cc engine which i figures must only weight 50 kgs and produced approx 260bhp.
Dave's probably right. Although one or several of the <2007 F1 V10's probably went over the 1000bhp per 100kg mark.
One thing hillclimbing has proved time and time again, is that brute power to weight is academic if the way the engine delivers the power, or the logistics of it's design (low c of g, it's installation, the gearbox needed to transmit the power) is wrong for the application.
Mr Wight, who posts on here can attest to that. A few years ago he bought an ex DTM Opel/Cosworth 2.6 V6 into the sport. The combination of a lighter nimbler chassis with a more "drivable" engine compared to the 4.0l V8 brutes that were popular at the time, wiped the floor with everybody and reset the standards of the sport. True, eventually, higher BHP won the day. But not before the point was emphatically made.