The sirio evo 4 is insanely fast, jilles groskamp used it at the last dutch nationals.
We have a speed trap in the track and he reached 110Km/h
He did have trouble making the 5 minutes though.

For me it's the JP stock engines, with the 2602 pipe and the ifmar crankshaft these engines are also really fast. On top end no one will pass me, i can overtake guy's with mf engine and last race i was faster on the straight then a 353 engine. And that for a engine which cost half of it.