Since a lot of 986Forum owners seem have the Top Speed Pro 1 catback exhaust, I thought I'd publish my results (before and after dyno runs).
1999 2.5L base engine, 135000 miles, underdrive pulley, LWFW, spec clutch, otherwise completely stock. ONLY the catback exhaust was installed, stock headers and cat's still installed (early cars like this only have one cat per side). No cat delete pipes. Nothing else was changed between the two runs.
Each major vertical gridline is 10 hp. Lefthand vertical axis (HP) not labeled for competitive reasons. A/F Ratio scale has been adjusted.
The green line is the stock muffler, the red line is the Top Speed Pro 1. The squiggly red line is the A/F ratio with the Top Speed exhaust. We did not measure A/F ratio with the stock muffler (other green line is flat).
Net result: +7hp @ 6150rpm. Peak +2 hp. All of the gains come above 5800 rpm. No appreciable difference in hp up to 5800.
I find the sound of the Top Speed catback to be awesome throughout the entire RPM range, though sound preference is subjective. The Top Speed exhaust also saves 18 lbs in weight. For $315, its a great deal.
