Being that you got some negative- I will try to advise.. What year RC-51 do you own?
OEM SP-2 is 2 1/4 or 57mm with a D-shaped inlet.. Which is an (dyno numbers) 8hp on the top of the RPMs.. The SP-1 exhaust header doesn't have the D-shape.. And has smaller cylinder head exhaust ports/ except were the header bolts to the head.. You gain the benefit of the D-shape pipe
This is the reason I specified using the SP-2 OEM header -reguardless which year RC-51 you own..
THE ONLY benefit to a FULL EXHAUST SYSTEM is at full throttle.. Which / sorry.. I have not been able to do - for long periods of time (ON THE STREET).
Building a header/ IMHO is pointless/ time "IS" money.. You are going to spend more time/ than you could just buying a SP-2 header from WHOMever...
Last edited by 1971allchaos; 02-04-2012 at 10:59 PM.