Here's an interesting take....
Details are scarce, but this Jet Ski is powered by a V8 made from fusing two MV Agusta F4 1078RR 312 engines together. The resultant 2156cc, 308bhp, carbon fiber–hulled monster is called the F4 Interceptor. Motorcycle engines have long served duty in jet skis. Previously, the most powerful was powered by a 250bhp, supercharged Kawasaki ZX-14 engine with a top speed of 68mph.