Basic kit for improving the performance of GX390s, 420 Predators, 13/15 hp Chinese OHVs. Simple to install and provides a significant performance increases

As step up from the Stage 1, this kit is designed to improve the power for the GX340s and GX390s along with improving the durability.

The Stage 4 kit starts with package similar to that of the stage 3 but adds a Ported and Milled Head with stainless, stainless valves, stud kit, & HD valve train components. This kits allows up to 35+ HP out of a GX390 and 40+ out of 420/440cc engines.