add power/speed on 1994 BMW 325is

what would be the best parts to use for gaining power/speed?
and if i put a new muffler on it what would be the best for bmws

Asked by for the 1994 BMW 325is
1 answer
Running highest octane fuel available and freeing up the intake and exhaust would be the best step

Anything further might reduce the market value of your car and running values