Need help finding horsepower gains for a magnaflow muffler.

I looking into buying a magnaflow muffler. It specs are: 2.25" inlet single 4" dia. circular, 4" long straight cut double wall tip. I heard a good muffler averages about 10 extra hp. Does this muffler fall under that category? Also, I have a '98 civic EX if that helps.

Unfortunately, very few cars can gain 10 horsepower from a muffler swap. Some cars from the '70s when cars were fitted with notoriously bad mufflers and powered by extremely detuned V8 motors could do that. But these days, manufacturers are doing a much better job at selecing mufflers for their cars and designing mufflers that keep the sound down without sacrificing performance.

If you're curious, you could stick a pressure gauge in your exhaust and see how much your muffler is holding you back. There's a couple kits to do this if you don't want to cobble something together yourself, starting at around $50. If your backpressure is around 1 psi or so, your muffler is not slowing you down. Note that if you add serious internal mods or forced induction, this could make a muffler that previously was adequate no longer acceptable.

Without any measurements, I'd guess you might gain 1 or 2 horsepower at most.

You will gain mostly noise thats about it. As Slanter said car companies are pretty good these days designing exhuast's and intakes for that matter as well.

You need to get the car on a dyno to get some base hp numbers.

Also don't do "ricer" math. ie if the muffler claims 10hp and an airbox claims another 10hp you did not add 20 hp to your engine. It doesn't work that way.

I have the magnaflow too and love it, they are cheaper on ebay but I wanted a warranty(salt in winter kills an exhaust) so I got it here. magnaflow 17905, or you can try one of the vendors :thumbsup: