What to tell the exhaust shop.

I agree. And testing has shown that Flowmasters don't flow that well. Dynomax Super Turbos flow better than most Flowmasters, and are quieter than the Ultra Flows if that's important. Another chart:

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That's one of the charts I was referring to when I was talking about the Ultra Flow numbers. Kinda hard to wrap your head around, but I'm sure it's accurate. You know how technology and all that goes nowadays.