Well I wanted to add some rumble to the Jeep. I kept the stock tail pipe size. I think it is better for lower end torque. I ended up getting a 50 series for a mustang GT. It works great and is not to lound on the highway. The Flowmaster 50 Series Delta Flow muffler is designed to produce a mellow, deep sound in most vehicle and truck applications. It is milder than the 40 Series mufflers on the outside of the vehicle, and is significantly quieter inside the vehicle, yet it still has the right performance sound and feel which is achieved with the use of a special Resonant Tuning Chamber within the muffler. Performance is comparable to the 40 Series.