Engine for Super Nitro
The Picco .15 Rear Exhaust engines work really well. Problem is they've been discontinued by Trinity, though some shops still have some left.
In General, a .15 engine of the same manufacturer, will have more Torque than a .12 engine of the same type (smallblocks).
Sirio has a .15 Rear exhaust with a Standard Crank that will fit in the Super. Claimed 1.7 HP!!!
Not sure if they're out yet.
In MY Super, I have the 2003' Fantom .15 Side Exhaust and it is a very Powerful engine, even for the price.