"Why are the 2023 Acura Integra's Exhausts Are Shaped Like Curly Fries?"
https://www.integratalk.com/threads/why-are-the-2023-acura-i...
Excerpt:
By snaking the exhaust piping into that circular route, Honda is lengthening the exhaust pathway, lowering the resonance frequency without using a traditional muffler . Honda engineers tell us that the design as first installed in the Si also emphasizes the 300Hz to 600Hz frequencies "to deliver a more aggressive sound." Skipping the muffler, Honda also was able to achieve that sound with a 27-percent increase in exhaust flow.
I bet this saves the money, too; a muffler is an extra component you need to source and/or build. Bending some extra pipe seems a lot cheaper.
Now hold on, extra length on the exhaust manifold / headers are not going to reduce sound so much you don’t need a muffler. And the muffler is far from the most expensive part in the exhaust system, which would be the catalytic converter.
For the gotchas - I'd guess that the exhaust manifolds would make a huge difference in terms of sound, and they seem hard to simulate. For example, engineers tune the individual per-cylinder exhaust distance - this way, the exhaust fumes from each individual cylinder align nicely once the exhaust from each cylinder merge into the final exhaust pipe. Otherwise, if, for example, the firing pattern is 1-5-..., then the air from cylinder 1 might arrive to the exhaust pipe at the same time as air from cylinder 5, given high RPMs and limited speed of sound.
And the fluid dynamics of the cylinders are something that is extremely critical to modern cars, too. And I'd guess that this is where things like misfires can be simulated.
Disclaimer - this is all based on my highly unsophisticated mental model,