I'm thinking about installing a 3 inch cat back exhaust I already have the gt500 mufflers on my car. would I be loosing a lot of back pressure and loosing some performance or would I actually gain anything?

 

zero gain. your stock 2.75" piping is already pretty much too big for your GT. The GT500 uses the same 2.75" piping your car already has. You'll need around 500hp to even consider the need to go bigger than 2.5", and 2.75" would need north of 650hp. 3" would be good until over 800hp. you're at half of that roughly. it's overkill. Even at those numbers (650rwhp for 2.75" you aren't leaving much on the table not going bigger. you could in theory go down to 2.5" piping and have enough to support your GT.

 

You will not gain anything in performance but your sound will be a bit deeper.

 

Ok thanks for the info what about headers is that something to put money into or factory ones are good enough

 

our cars have factory shorties. do them if you have a hole burning in your pocket. you can spend a lot of money to make a minor gain N/A, but all of it only gets really awesome if you have a power adder.

 

What do you mean by power adder?

 

power adder= Supercharger, turbo, nitrous. As far as headers are concerned. You'll see aprox. 20 Whp.gain. Have you tuned the car yet?

 

If you're going to do headers at least do long tubes.

 

No I haven't tuned the car yet I'm new to v8s so trying to learn the best ways to ad power without supercharging it or turbo

 

Longtubes are an excellent addition to a N/A or boosted mustang. They have a decent amount of power and sound to be gained. Shorty headers dont really do much for you. I mean if you are going to go through all the trouble of getting under the car, unbolting the factory headers, tuning it (which is 100% necessary), and bolting new headers up, then go ahead and go the whole 9 yards and get the most out of ur time and money. Get longtubes. preferably ceramic or natural finish. its not really an easy install either.

added bonus: its awesome to open ur hood and show who ever those longtubes going down the side of the engine.