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Ryan,

Thanks for posting this...it goes to illustrating my point made on the header thread how a too small collector will (for want of a better word) "FORCE" the motor's torque to Peak at too low an RPM which acts like a cork onthe rest of the higher RPM Horsepower curve. Looks like the 3" collector peaked at 5300 where the 3 1/2 peaked up around 5900....look how much power that is.....I know the bigger ones are stepped but I'll bet 80% of the power gain was from the larger collector letting the motor keep "feeding".



Hard to say without knowing the primary lengths, I'd think the primary's dictate the RPM more then the collector size... But if they're close to the same, then you're definately right.