Stock Frontier Exhaust System

One of the oldest tricks in the hot-rodder's book is to open up the exhaust system to allow the engine to breathe better; moving more air usually translates into more horsepower.  For street engines, however, more is not always better.  If the exhaust diameter is too large, for example, the exhaust stream velocity will actually decrease, resulting in a loss of low-end torque.  For an excellent article on performance exhaust systems, click this link to Proficient Performance.

The exhaust system on the 2005 Frontier V-6 has a decent sound, but it does have a few very restrictive areas, all located in the Y-pipe.  For this reason, it appears that merely replacing the stock muffler with an aftermarket unit won't result in any significant performance gains.  To view the Y-pipe you can slide under your own truck and take a look, or you can peruse the pics below:

The stock Y-pipe exits the catalytic converters in 2" tubing and the left-side pipe has to make a 90* turn to join with the right-side pipe.  The pipe has to narrow down to make a clamped joint just before the "Y", then makes another 90* turn toward the muffler.  The actual "Y" junction of the two pipes has a crimp that looks to be very restrictive; for a closer look, see the pic below:

To see how Gibson designed their Y-pipe, see the photos below; you'll note that the bends are smoother, the pipes are larger diameter, and the actual junction of the two pipes is much cleaner and more open:

 The Gibson muffler is less restrictive (they don't have to meet Federal noise restrictions), and the exit tailpipe is larger diameter.  It's easy to see why the Gibson system flows the exhaust more efficiently; will it produce more horsepower?  Stay tuned for the dyno results...