Awesome. I heard the R4 has a punchier top end. Ijust purchased the kart and it came with the R2so I will give that a try for now. Does the R2 make less power in general or just make the power in a different RPM range like the midrange? Thanks for the info with the sound. I have a 12″ RLV on there now so I prob will have to pick up a 14 to run at F1.