Audi Sport 90 Back Pressure
 

Alright... basically im looking into a new exhaust... my plan is to stay cheap and only buy essentials... right now ive the complete stock exhaust and have a cherry bomb muffler to work with... what i was thinking about doing is taking out everything from the ressonator to the muffler, and in place of the ressonator, i would put the cherry bomb and then just straight pipes out the back... would this kill my gas mileage and performance due to the back pressure... if anyone can give me a estimate at what a good backpressure would be and possibly how to calculate it, that would be great... thanks in advanced...