... well wonder no more. The Vincent Foucart 205 V16 is your answer:
It's based on a tubular chassis and uses four de-stroked CBR600 engines put together
The whole car:
A shame there's no word on power output...
EDIT: there is. According to one of their competitors, power output would be 437hp. That's twice the specific output of a Honda S2000!
That power is channeled through all four wheels and a 6-speed sequential gearbox.
Photo credit: Rallye TT