Nope...actually some of the dyno's have shown LESS power. Most people think it makes a difference because of the sound. Its louder, so it must be faster right?
Once again, think about my example earlier. You've got a 2.25 inch hose, and add a 3 inch hose to the end of it. Is the air flowing out of the hose any faster? The stock mufflers are not a restriction because the flow is divided. We've got a false dual exhuast. 2 pipes to 1 pipe to 2 pipes.
Here's a shot of the exhaust...one look at this convaluted mess, and you realize why catbacks do absolutely nothing.
The catback is actually the "LEAST" restrictive part of the whole exhaust.
Two inefficent cast iron exhaust manifolds with a precat on each one, plus a whole hella lotta stupid bends...giant dents in the pipe (from the machines which mounted the pipes) followed by some sort of "pre resonator", finishing with two main cat's.
And thats before you get to the two mufflers and the main pipe/resonator.
Replace the manifolds with headers, the two main cats with a single highflow cat...THEN the restriction will be at the catback. Wagners current header development is promising some excellent torque gains, and should be done in the next few months.
Based on the available dyno's, and the # of magnaflows being resold (people getting rid of them and yet still owning the car). I'd say they give about a 2-3 hp MAX gain...about the same you'd get from swapping your transaxle and engine oil to full synthetics.
