not an engine suggestion, but a suggestion for a engine curently in game
the old vtwin sound was beter, the one we curently have sounds like a flat plane v8 with a misfire on all cylinders, or it sounds like a strange mix of a electric motor and a jet or something
so i say, bring back the old sound or impliment a new sound
another thing that could help make decent sounding engines is using ATG's engine simulator, its code based but its fairly easy to use, so easy in fact that i with just a few hours of tinkering managed to figure out what many things do,
and yes, i did make a vtwin with what i hope are similar specs to the hardy vtwin, and yes, it sounds amazing compared to the curent vtwin sound in game