H or X CROSSOVER?

340sFastback said
TTI headers, TTI 2 1/2 inch H pipe, Ultra Flo mufflers, TTI 2 1/2 inch tail pipes with tips, no drone. Ultra Flo on my car not loud at all unless I go wide open throttle and even then the roar from carb sucking in air is much much louder then the exhaust.

Dynomax mufflers that are offset in and center out have a botched up flow when exhaust crosses over the center outlet internal to the muffler. Cut one apart and you'll see. Dynomax offset in/offset out have a much nicer internal path for exhaust to travel.

I don't care for that exotic car sound of an X pipe but that is a subjective opinion because other people love X pipe sound.

340S, When we did our testing it was on GM style offset offset. I was running the Dynomax 17748, which are offset center, on my 69 340 S fastback. A recent test with similar "turbo-stye with flow director" mufflers and comparing the offset offset to offset center showed it only had about a 1 to 2% loss when it has that pipe in the flow path. I guess it makes sense since air likes to go aorund round objects and since the muffler was 4.25" thick and the pipe was only 2.5" OD, it was not as much flow restriction as I would have thought. So, I no longer worry about the 17748 to 17749 and 17733 and 17334 Dynomax SuperTurbo differences.