The exuast might be holding you back. Idk what that type of exhaust as far as the muffler puts out. But when i had a muffler stuck on the end of my car vs a cat back. I had full exhaust and intake i dynoed at 131whp. After i changed it i dynoed at 138whp. Paid a lot for the cat back went with skunk 2. I highly recommend it btw! umm i went and got a new clutch and 7lb fidenza flywheel for 230. Made a HUGE DIFF!! they said i should be at 155whp now