4st engines are much cleaner than there 2st counterparts the smaller amount of slime I clean off my planes tell me that,also the props I use on my 4st engines will bog the 2st equivelent reducing the HP produced through higher rpm.
if you are crashing your planes then you need to either inspect them closer for potential problems and correct them before they become fatel and practice more, things happen of course, but it seems alot of them could be avoided through due dillegence something my club preaches quite a bit.