[userbinator]

You can model it as a series of tubes of different diameters.

Look up "digital waveguide" for some more details. This technique is mostly used in speech synthesis, where it can make pretty realistic human-speech-like sounds by modelling the vocal tract, but there's no reason it can't be applied to a car exhaust system.

[ynniv]

The better car simulators already do this: “Physically informed car engine sound synthesis for virtual and augmented environments” https://air.iuav.it/bitstream/11578/264484/1/SIVE15_submissi...