Postby smj999smj » Thu Mar 02, 2017 12:24 pm
Honestly, I didn't really notice much difference in performance nor gas mileage even after I installed the Doug Thorley shorty headers, replaced the rear cats with Doug Thorley mid-pipes and replaced the factory main muffler with the Magnaflow 12580. It was definitely louder, which increased after several hundred miles, and sounded great at WOT, but I just didn't feel like the vehicle was much faster or fuel efficient. In fact, I initially started driving more aggressively because of the exhaust, which hurt fuel mileage. That doesn't mean it didn't create more power; only comparing before and after on a dyno would prove that. After that, I installed the XTP plenum spacer and aFe Momentum air intake system and it did seem to wake up a little. It wasn't until I got the Superchips tuner and went with the 93 Octane performance tune with a 3 degree timing bump that doing the mods really seemed to make a difference. So, my advice would be unless you are planning to do other mods and a tuner to increase performance, the stock exhaust is just fine as it is, unless you want to deal with a lot of exhaust "drone" at low RPMs.
One thing I've looked at is the possibility of installing the V8 muffler (a 2 into 1 design) onto the V6 model. It looks like they may join at the same point between the rear converter flange and the flange of the muffler pipes. Since the body is the same, the piping behind the muffler and the muffler location should be the same, as I see it. I would think the swap would result in a more livable sound, if you don't care for the loud, aftermarket muffler drone. Unfortunately, I haven't had a V8 model to do any measurements or direct comparisons to my V6 Pathys.