The Good-Win description for the Federal 49-state version of the Roadster Sport High-flow CAT states the diameter of the CAT pipe is 2.5-inch; but what is the diameter of the OE factory CAT pipe? My Miata is in the body shop recovering from a very solid hit in the right-rear wheel well by a Z06 Corvette, or I would go out and measure the factory CAT pipe myself: http://www.youtube.com/watch?v=F-ZDH9Jb ... VDghmW-NwQ .
I have a '95 track/street Miata with a very strong running '97 engine which has the head milled 30/1000s inch (compression ratio after milling should be about 9.8:1), plus I designed and installed a very free-flowing CAI (based on the K&N enclosed universal Apollo model intake) that sucks 100% outside air via a three-inch duct through the cowl -- and that free-flowing CAI is paired with a very free-flowing Roadster Sport 3 CAT-back exhaust. What kind of rear wheel hp boost -- if any -- might I expect with addition of the 2.5 inch Roadster Sport High-flow CAT (the current OE factory CAT has about 110K mi on it). My 69K-mi '97 engine now shows 148 peak HP at 7000 rpm and 124 foot-lb torque at about 5200 rpm (110 at 7000) on a Mustang dyno (raw dyno power numbers were normalized to sea-level and 77 F air temp vs Tucson elevation of 2500 ft and air temp of about 90 F when dyno tuning of cams was done).