MagnaFlow Exhaust Flowbench Test: Does a Quiet Muffler Impact Airflow Performance?
So this was a highly informative video. I know this is in a way, marketing for Magnaflow, but reserve your judgement until you watch the video. There's some interesting info in there with regards to airflow, as well as how offset designs can affect airflow.
So the size of the muffler doesn't affect airflow as long as it is a true straight pipe design. As soon as you introduce some bends into the flow, like on mufflers with offset inlet/outlet designs, you lose a bit of airflow compared to a straight pipe design.
Another interesting bit of info is that chambered resonators, which introduce obstacles for the air to flow around, flow less air than a straight through design.
Okay, I see where Magnaflow is poking at Flowmaster here, because Flowmaster typically uses chambered resonators. But again this doubles as a marketing video for Magnaflow, so take that with a grain of salt. For all we know, Flowmaster has figured out a way to make the air flow just as well using chambered resonator designs. But my basic knowledge in physics bear out the idea that, a straight through/pipe design will flow more air than one where the air has to go around obstacles.
Anyway, where was I? Ah, typically, OEMs will use chambered resonator designs. Great for reduction in exhaust volume, but not so much for performance. If you're driving a car with a turbocharged engine, you want straight through mufflers to get the best performance out of your turbo.
Knowing that, I now see why some aftermarket exhaust systems flow better and sound louder than other designs. It's all in the design of the mufflers, as well as how much bends there are in the exhaust system as a whole.