If I replaced the factory muffler on my 97 Ranger with a cheap parts store turbo muffler, would I see any appreciable gains in power or mpg? I suppose it all depends on how (if at all) restrictive the stock muffler is. Also, how much louder would a turbo muffler be than the stocker? This is the only thing that's really kept me from going ahead and doing it already, since IMO the only good sounding 4 cylinder is one I can't hear.
I found the aftermarket turbos to be very effective on some vehicles, not so much on others. I have a habit of buying an oversize muffler and sleeving it down to match the pipes: the larger muffler seems to cut back on backpressure and run quieter. Mind you, I always drill a 1/4" hole at the back to allow moisture to drain out...
I got an el-cheapo from Advance that fits my 2.3. It also fits the 302. I figure if it can handle 302 cubes of exhaust, my 140 will go thru easily. It does, and I think it has more power. Factory quiet, too. Best $20 I ever spent. Don't like the rusticles in the eye, though.
I replaced my exhaust from the manifold back with 2.5" aluminized steel with high flow cat/2.5" cherry bomb muffler with a 3" tip turned in front of the rear wheel. Got about 1-2 mpg more and lots of mid range/top end power. Lost a little bottom end but thats ok with me. Although the sound police and neighbors dont like me.