RE: roto start on a mammoth?
HPI engines...I think Force makes their engines...I mean the Force .21 and Force .26 are exactly the same as the HPI ones in the Savage's.
XTM's engines are made by SH Engines in China actually...SHOCKING ISN'T IT? XTM and SH probably used a Force engine to design their engine. It's not an exact copy on the inside, but the Pull start is similar.
1 major difference...Force/HPI uses steel backplates, while XTM/SH uses plastic, nothing wrong with plastic though...
Also another fun note: SH Engines makes the Mach .26 for Dynamite/Losi/Horizon Hobbies.