If you are concerned about maintaining exhaust velocity (the real aspect at work to that whole "backpressure" element), what you do is keep your stock pipe size, but you can up-size your muffler (an SRT8 component, for example). Naturally, you will need adapter couplers to connect from your stock pipe size to a muffler with larger core pipe size, but that's how you do it. The pipe size is nearly never the bottleneck unless you are dealing with tiny 1.5" size or something. It's the muffler that is the bottleneck (where sound attenuation is typically at direct odds for maximum flow that muffler could accommodate).
09 Challenger R/T automatic...4 tires, stick-on convex mirror, seats
It's not that I really needed 370 hp...but having 150+ hp riding shotgun at a moment's bidding w/o a 6000 rpm moonshot is what makes me feel like I'm in the right car for me. The roar of a v8 seals the deal!
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