Roadster Sport High-flow CAT for 94-97 Miata

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Roadster Sport High-flow CAT for 94-97 Miata

Postby Aruba » Wed Jan 01, 2014 1:33 pm

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: ... 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).
1995 Miata 97 Miata engine with head shave, RoadsterSport-3 CAT-back, custom CAI = Mustang Dyno SAE numbers-148 whp at 7000 rpm, 124 ft-lbs torque at 5200 rpm.
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Re: Roadster Sport High-flow CAT for 94-97 Miata

Postby Brian » Thu Jan 02, 2014 3:30 pm

Head mechanic Rocky recalls stock is 2.25, my recollection was that it was smaller than that but don't have one here to measure today. Regardless, I don't expect you would dyno much improvement going from 2.25 to 2.5 unless your factory cat is in failure mode and clogged. The point of moving to the bigger size was for customers running boost to have the entire system 2.5 all the way out.
Brian Goodwin
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