2 When it comes to the mufflers, there are many options to choose from in the Flowmaster line. Josh says "You want to look at the muffler's overall dimensions and check that against the space you have available under the car." This shot shows the difference in size between the 50 series (bottom) and the 40 series. The 50s are quieter, but are too big to fit without dropping them closer to the ground. We wanted a more agressive sound anyway, so we used the 40 series and also kept our ground clearance.