You can run whichever you like. If I recall correctly, SLP longtubes are meant to go with their X pipe and it is a direct bolt on connection, but you can always get a good exhaust shop to fabricate an H pipe for you if that's what you want to go with.I like the idea of adding a catted mid-pipe and full lenght headers (to my existing SLP's) - a few questions:
Should I run an X or H midpipe (can X come with cats)?
I cannot give you a definitive answer to this question, as SLP are the only headers I've had experience with. I can tell you that they are wonderful quality. I don't know about gains because I have not ever put my car on a dyno.How does the SLP full length headers compare to other brands?
If you run the long tubes/catted X/Loudmouths you will undoubtedly have the loudest Mustang in town, to put it bluntly. Just putting on the Loudmouths sounds quite louder than stock, but adding the headers and midpipe really make the car scream.How much louder is it....? When I installed my SLP (replacing my stock mufflers) - I had a grin from ear to ear...what can I expect from the headers/mid pipe?
Since he was running an O/R pipe, there was nothing there to muffle the sound. No cats + no mufflers = a horribly loud exhaust (and not in a good way). Like I previously said, I run a catted X and it is almost on the verge of being too loud.Stlwagon - what do you mean by god awful (I hope this is a good god awful) - why did you get rid of your SLP loudmouths?