I was thinking the opposite of your theory. I was guessing that since I have twice the area for the sound and air to escape from that I would need either the same amount of mufflers as someone with a single exhaust or possibly more because it would be like running a 4cylinder on a single 3" which usually shrieks. I like those AP mufflers they just don't have anything that will use all my provided space. I remeasured last night for about the 11hundreth time and I think I can actually squeeze 30" off muffler case length. I will have to chop the inlet and outlet down to almost nothing and welding it will suck but I'm gonna try doing it myself. My neighbor has a 4 post lift so I'll haul my little Hobart over there Friday and give it a shot. I am going to call Magnaflow today and ask about the 7x7x30" round 3 chambered/straight-through muffler. That gives me the most possible area of muffling, but I'm confused as to why it says straight through but also 3 chambered. I found 1 picture from amazon that shows that it is indeed straight through but I want to know why they list it as chambered because I think a key to cutting resonance is having some chambers for the sound waves to reflect off of. Also still probably going to cut the unknown cats out because I'm not sure if they are real cats or just shells to fake out the Texas emissions losers, either way, they are half the size of the vibrant ultra flows which I will replace them with.
Also, another reason I'm a little skeptical of the AP mufflers is I can't seem to find anywhere that shows exactly what they are packed with, and this truck will likely see boost of some flavor in the next year or two. I've had good luck with the magnaflows and vibrant not blowing/burning the packing out. Not sure how the APs would fare under high EGTs.
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