What give the subaru wrx sti dat unique rumbling sound?

Exhaust tuning

l believe your referring to the boxer rumble. This is caused by its unequal length exhaust manifold.

Take any boxer engine & slap on a free-flowing exhaust system, & u will get that distinct rumble. Even a ''tame'' Subaru (like a stock non-turbo Legacy) has a similar ''boxer rumble''. The cause of the sound is not just due to the length of the exhaust manifold--a lot of engines have unequal-length manifolds yet do not sound like a boxer engine.

An inline four has the four cylinders in a row, facing the same direction. The result is an evenly spaced firing from all four cylinders, creating a smooth, even pulsing in the exhaust--and hence, no ''rumble''.

However, a Subaru boxer engine has two cylinders on each side of the engine, facing opposite directions. The firing of the cylinders is still even, but the firing order has the two left (L) cylinders firing one after the other, followed by the two right (R) cylinders, & so on: L-L-R-R-L-L-R-R. In each of the two exhaust manifolds, the result is a ''pulse, pulse, wait, wait'' pattern.

So in addition to the even pulses from the four cylinders one after the other, there is a second left-right pulsing at half that frequency. That is the souce of the boxer rumble--it is like combining the sound of an inline four-cylinder engine with a two-cylinder engine.

The 3rd guy had it right on. Just wanted to comment to why the first 2 are wrong.

Exhaust tuning. has nothing to do with it.

An equal length exhaust manifold on a Subaru would make it sound like a Honda. FYI.