It fits in the same space and uses the same engine mounts as a .12, but the comparison ends there. To start with, the Pro.15 has a 20% larger displacement than a .12 engine. It includes such high-tech features as a grooved oil-ring piston for long life, a trick machined aluminum cooling head, ball bearings, finned aluminum backplate*, and a channeled-beam connecting rod which improves oil flow. The carburetor is all new, with a larger 6mm intake and reuseable low-restriction foam air cleaners. Double O-ring seals on both the high and low-speed needles eliminate power-robbing air leaks. The Pro.15 is an incredibly rugged and long-lasting powerhouse, with its strict quality control, ABC (aluminum, brass, chrome) construction, and the toughest recoil pull starter in the business*. The TRX Pro.15 comes in four tire-shredding versions, to fit almost any application, including any .12 equipped Traxxas model. Covered by a Two Year Limited Warranty and a Lifetime engine replacement policy.