On my GRP.28 I run a fioroni 70/30 split clutch with 3 standard springs, GRP 4 & 5 PLUG (usually #5) 30% byrons gen2, the jp3, or dyn 053 pipe. The GRP.28 is a great .28 engine. With the standard fior. clutch springs this engine has a very soft bottom end but great overall power. Compared to the old Nova 528 xr, JPX 28, OS 28 it has a much smoother power delivery with better run times, but does not feel it has as much power as the others I listed.