You are not going to find much of a performance increase just by changing the cans. You really need a full exhaust.

From an engineering standpoint, I think Tyga and HARC PRO (they make TSR's pipes also) has it wrapped up. Their pipes are excellent! The newest JHA and Dogfight pipes are just as good, but the older sets are lacking a little. For the money, though, the Tyga's are hard to beat.
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Paul Herr
2000 Honda RS250
1994 NSR250SE, far from stock.