I'm using G4S too and I'm very satisfied with the performance of the engine. I'm using Skyline VR12Plus pipe, black extra hard clutch spring, red hard clutch shoe, two weights installed in the fly weights, and 1.6 mm preload. My gearing is 18T first gear pinion and 25T 2nd gear pinion, with stock spur gears. My track is fairly big, with very long straight. I try mugen 2501 pipe too, but with skyline pipe I can adjust the engine more stable manner. Good luck.