Hi so on my 2003 GT i still have all four of my stock cats, and i'm planning on taking those off and putting two high flow cats on there to give it slightly more volume. so my question is , is it the same to just keep the stock h pipe and put the two cats on it or would it be better to buy an offroad h/x pipe and just have someone weld those onto the pipe for me.Would there be any difference in sound???

 

Running no cats will be louder for sure. The factory midpipe is 2 1/4 diameter btw. Typically, a x pipe will be raspy while the h pipe will be a more throaty sound. This will also depend on the mufflers. Remember if you go with an offroad midpipe, it most likely wont pass emissions while most aftermarket catted midpipes will aand they are 2 1/2 diameter. Personally, I would buy a complete aftermarket midpipe, whether it be offroad or catted.

 

I would go O/R. I bought a catted mid-pipe and the cats went bad in a couple months.

You're probably better off going O/R and putting the stock mid back on for emissions.

 

I purchased an o/r midpipe back in early 2009, noticed how loud it was, how the car felt in the low end, and how it sounded at a certain rpm paired with the original 40s that I had at the time. So I ended up getting pypes high flow cats and having them mounted onto the midpipe. Imo the car sounded and felt quite a bit better and I didn't have to worry about the inspections also. I later changed the mufflers to the 10series though. But those cats have been on there since that time in 2009 and I haven't had an issue with them. And I later the next year added boost to the car. So that's 5 years on the car n/a with after market cats and 4 years boosted. Those are the pypes ceramic cats.

I have been running Magnaflow Ceramic high flow cats on my TBSS for well over a year. Its not boosted but they are aftermarket cats. The aftermarket cats are not nearly as quiet as the factory cats. My wife had factory cats on the TBSS she had and it sounded quite a bit different than my truck. The factory cats I had on my car sounded quite a bit different than the aftermarket ones I added later but I also changed out the factory mid to an X. Aftermarket cats don't clean up the exhaust(or quiet the exhaust) nearly as much as the factory cats.

 

Regardless of cat or catless, I would get an aftermarket pipe and be done.