Couple questions -
- What kind of x-pipe crossover are you using ( brand matters due to location)?
- Cats - are you opposed?
- Sound deadening - do you have any?
X-pipe design matters. Without getting too deep into standing waves and speed, the practical side is that X-pipes like the
BBK have a
resonance with the 302w. This will change once you introduce a turbo to the exhaust stream.
Cats def take the edge/sharpness off of the exhaust sound too. If you look for the 6cyl Jeep Cherokee replacements that are CARB EO certified, the bodies are short (4") and 1 is certified for more GVWR than any mustang. Why this particular cat? It's small, can handle the heat, isn't junk, doesn't require AIR like the stone age cats that came with our cars. And because of how small it is, you can work it into the stream wherever you want.
Mufflers - Pretty much any non-chamber muffler will be good here. The larger the case volume, obviously the better. The Fox platform is limited with muffler space under the car. I'm a fan of the
Borla ProXS line personally. Pick the sound you want* (
see my last point below)
Sound deadening. Our mufflers sit up under the rear seats and have a sheetmetal wall that they can resonate through. Fix THAT. Add some sticky mass like Vibro to change the panel resonance, lay some MLV like Second Skin on top of that, and then stuff under the rear seats w/ some denim insulation. Do the same for the trunk/spare tire area. Done right and you won't hear the fuel pump from inside the car anymore.
Lastly...once you get your turbo's plumed and the car tuned, download a spectrum analyzer on your phone and go drive around. You'll very quickly find the resonate frequency that is annoying (it will spike, in Hz), note the RPM that it's the worst. Use a fancy web calculator to come up with the pipe length for a 1/4 wave resonator (aka a side branch). Go to an exhaust shop, have them weld that into the mid-pipe. You mentioned cut outs....put the cut out at the end of the resonator pipe and you'll get the best of both worlds.