It should also be said that all X-pipe designs are not created equal. Most are just jump on the trend/copycat designs, and some are truly awful. Even slight differences in X-over location, X-over size, angles, they all make a difference. This doesn't even get into some manufacturers lazy workmanship.

There was a good thread on this at Speedtalk a while back, and i think the general consensus is that it matters which one you get, where it is put in the system, and how well the rest ov your system is designed and built. The results CAN be good, and 12-15HP doesn't seem out ov reach, but do it wrong, or buy the wrong brand, and you'll quickly negate any benefit or possibly end up with less power.

But... done right or wrong, they sound damn cool, though some people dont like to lose that low old-school rumble. They quiet the system up, which again, some like and others dont.

My Charger picked up serious power going from no X-over 3" press-bend to an X-pipe 3" mandrel. The brand i used was a bad one and i would never use it again. It was cheap, and i got what i paid for. Sounded really mean, even with the junk 440.

My girl's 96GT Mustang went from the stock 2 1/2" H-pipe to a Dr. Gas 2 1/2" X-pipe and the difference was immediate, even going from Borla dumps (on the stock H) to a full Spintech cat-back (on the X). The sounds was/is absolutely glorious... even on a stock 215HP 4.6L.

I highly recommend Dr. Gas. You'll pay 3 times as much as Dynomax... but again, you get what you pay for.