Yea, they are better than OE, but you do a lot better opening up the exhaust system. Headers, high flow cats, and free flowing mufflers, (NOT Flowmasters) X pipe, will all help. You need a muffler that you can look straight through before installed. If you look inside and see stuff in there this will impede flow. You want your exhaust to flow as freely as possible. Keep in mind that an engine is just a big air compressor. The more air-fuel you can get into it, and the more exhaust, you can get out of it, the more power it will make.
