My opinion is
Dynomax; long 3-pass. mine are 3" all the way.
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my car is a manual trans and has run about every rear gear in the catalog, and with double-overdrive, down to the equivalent of 1.97 and even as low as 1.79, and currently 2.77. It has cruised as slow as 65=1450 rpm, and as high as 65=2870; all with the same Dynomax mufflers that TTI provided in their 3" dual exhaust kit, back in 1999. The cruise exhaust sound is a most pleasing at 2240, which is what I have been running for a few years now; no drone.
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My 367 has alloy heads and the dynamic compression ratio has run; as low as 8.75 and high as 9.23, and pressure from 178 to nearly 200 psi. In straight hiway mileage, she scoffs at filling stations. I used to fill it up at day's end after having driven all day on the same tankful. I figure that I got the cost of the alloy heads back before the end of the second summer, in fuel savings alone.
Eventually, I traded away some fuel economy for some top-end power, a thing I soon regretted after the novelty of said top-end power wore off, with 3.55 gears.
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IMO, the 262 cam is a good choice, with the price of gas ever-climbing, and
IMO, if you put some pressure into your 340, keeping the quench in check, she will love the 3.23s.