Okay, here are the specs for the two engines

Megatech NEO .16 ST

Max RPM 31,500
B.H.P. .74@29,500 RPM
Bore 15.1 mm
Stroke 13.77 mm
Displacement 15.99cc

HPI 15FE

Displacement 2.48cc
Bore 15.3 mm
Stroke 13.5mm
PS/RPM .56hp/29,00 RPM
RPM Range 3,000-32,000

So can someone tell me which ones better? It looks like the NEO is better, but it is such a pain to tune, any suggestions would be helpful