A stock Audi S4 and RS4 horsepower and performance from the factory is nothing to ignore. But if you are looking to get even more out of your car, check out all our aftermarket Audi S4 performance parts below. Need an intake? We have them. How about upgrading your S4 exhaust? Yea we have those too. Or if you are a serious car enthusiast and building a track car, make sure to check out our S4 gauges to keep an eye on your car's health as you tune it.