Basic kit for improving the performance of GX390s, 420 Predators, 13/15 hp Chinese OHVs. Simple to install, you can expect 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 kist allows up to 35+ HP out of a GX390 and 40+ out of 420/440cc engines.