From the Japanese side, I would say that the HARC PRO pipes are definately the best design (though unchanged since 1995), not to mention thier perfect construction. They are the benchmark over here the others strive to follow. The TSR pipes are actually made by HARC PRO, the only difference is they make thier own silencers.

As for the others, only the latest versions match the HARC PRO's in performance. The older versions are not real great. The peak numbers were usually close, but the HARC PRO design gave a little more mid and definate better overrev.

As for the Tyga's, well, Matt used to work for HARC PRO, so they have a great background. Tyga designed their pipes using TSR software, which was released in 1996. I would say their design is just a tad better than HARC PRO's, only because they implement the latest technology in pipe design. I have a set of the GP pipes, and absolutely LOVE them. Together with my recent overbore, it really brought the power alive in my bike.
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Paul Herr
2000 Honda RS250
1994 NSR250SE, far from stock.