Magnaflow Exhaust recently got their hands on a 2015 Mustang GT and strapped it on a dyno with the dyno graph (released with the consent of Ford) showing the 5.0L V8 putting down around 375RWHP and 355RWTQ in stock form. We now have the aftermarket exhaust company providing Mustang6G with many more details about the dyno.
Magnaflow claims its Competition Catback Exhaust adds up to an impressive 30RWHP/25RWTQ with OEM cats, no tune, no headers, and no other modifications. According to them, the Mustang GT was 100% stock with 30 miles on it and the original gas in the tank straight from Ford. The car was dynoed on a Dynojet in 5th gear with 1:1 drive ratio with the baseline dyno done around noon time in 80-degree weather and low humidity and the dyno with the catback performed two hours later.
How can a catback possibly add up to 30RWHP/25RWTQ you ask? Magnaflow weighed in on this also, stating the piping size of the manifolds and the entire exhaust is smaller than that of the outgoing Mustang, in part to comply with global noise regulations and resulting in sizable power gains left on the table. The 3 muffler/resonator setup (opposed to the previous 2 muffler/resonator setup) contributes to the apparent restricted power of the 2015 Mustang OEM exhaust setup.
Needless to say, if true, this is excellent news for S550 Mustang fans and provides an easy and affordable way for owners to add significant power and torque.