I hve a question what makes some cars sound loud but not others
In the game? The racing exhaust is loudest, then the semi-race, then sports, then stock. It seems that, in a lot of cases, the stock exhaust is too quiet - see my namesake for an immediate example.
In real life, it's that wonderfully broad field of acoustics, coupled with the breathing habits of the engine.
In short, as an example, the exhaust system can be likened to a filter network that attenuates and accentuates certain frequencies and gives a distinct sound according to the design intentions. On a racing car, at least historically, little mind is paid to the reduction of sound (from all sources) whilst the focus is on power output and reliability, so they tend to be pretty loud.
Also, generally speaking, the harder an engine is working (relative to its displacement), the louder it is, especially with regard to compression ratio, valve timing and all forms of supercharging.
