does anyone now the h.p. gains for any particular aftercat exhaust i'm looking to buy one for the 01 cobra i just bought (19$thousand with 45000 miles triple black convert) wondering which is best (gains) and which sounds best...any info much appreciated
For performance gains, definitely go with a straight-through design muffler (ie - Dynomax, Magnaflow, Bassani, Borla, etc, etc) instead of a chambered style (ie - Flowmaster) muffler.
For sound - go with whatever sounds best to your ears. The mustangexhaust.com website is a pretty good source for mustang exhaust reviews, sounds, videos, etc, etc.
The midpipe and catback are fairly restrictive on the 99/01 snakes but not nearly as restrictive when compared to a forced induction application such as the 03/04 cobras.
You will still free up a decent amount of power by swapping the midpipe and catback, at least I did (see sig).
If you're gonna leave the stock headers and stock mid-pipe on, dont expect performance gains. Just a couple horsepower. Youd be better off putting on some long tube headers and an offroad H or X pipe.
I spent $85 putting on simple 13 inch glass packs. The power gain over the stock mufflers felt like a turbo. even the 4:11 gears did not feel like this much power. I have had catless H pipe and 2 chamber flowmasters but with current Bassani catted x pipe with these glass packs the torque and power is the best by far. I drive 75 to 80 mph with no drone. As yall know the Flowmasters have a terrible drone.
I have to disagree about the power gains. I think a catback will give you some very good horsepower gains. Swapping out my mufflers for 3" Magnaflows was the most noticable power gain yet on my car.
If you want more power get a straight thru design like a Magnaflow catback. Chambered mufflers = piss poor flow, but some prefer the sound. I think the Maggies sound kick ass myself.
People will preach straight though = performance ....not so true, while you will get better power on the high end your low end torque will suffer.....greatly...as i had the full magna flow 3 inch system and i was quite happy with it on the high end it left something to be desired down low....if you're willing to spend the $$$ overall the best exhaust i've seen and now use is the ford performance dual mode system these mufflers have a valve inside of them that gives you the necessary restriction for throwing people into the seats at low end, and open wide for incredibly good topend power.....you should look into these as they were used on the infamous fr500 project (One of the most versatile and wicked cars built by ford for under 50k)