People are allready paying a ton on engines. A 4stroke deosn't cost $400.
I think dropping a couple rocks in the stock tank should even the expected run times to keep things intersting for tracks with shorter mains. But with 30min to 1hr mains it's a non issue. Your not going to get 15min run time, especially when supercharged.
I'm looking to make a kit conversion for Saito engines for the D8t and Mbx6t. but don't hold your breath, my stuff is 1.5+ years away. Mount, Cooling head, header, and a buggy center diff gear and a huge pinion/clutch bell. It alot of dreaming, and ya'll ain't the easiest bunch to please.
But I'm going to probally go bigger than the IFMAR rules allow. .40 seems small to me. .56 sounds better for truggies.