Ok, I am putting together a 421 Serval this month and will be dynoing it with Shearer small bores vs R-2s. The Bike will be a 421 Serval bought from M&M atv with Hinson Spring Loaded Basket w/Straight cuts, F.A.S.T. Clutch, Cut trans but not full override, Shift Star Mod, Billet Impeller, Stock Gearing 14-41, 34mm PJ's w/6" pods, V-Force reeds, Boss Billet Intake w/ built in crossover, Fluidyne over sized Radiator, NOSS Head w/ 24cc Domes. That's all I can think of for now so I will dyno it and run a comparison on these two sets of pipes. I'll keep you guys posted on the build and eventually the Dyno #'s.