Since the model's introduction in 2003, not much has changed in the 1NZ-FE powerplant that motivates the Scion xB; there are some ECU wiring differences and the SAE revised BHP rating for 2006, but essentially this engine has been the same throughout the entire life of the xB line. What was supposed to be a test of various available exhaust systems on a completely stock xB ended up being a test on a platform that already had an aftermarket intake As this is usually the upgrade path the xB owners take, we didn't think it necessary to convert back to the stock airbox to run the test; after all, the aftermarket intake system that helps release power when used alone should only be beneficial when testing performance parts on the same system.

It should be noted that we established a new baseline for this test; we didn't use the last run from the intake test and establish it as the reference point. It should also be noted that, for those exhausts that provide removable silencers or dampeners, we tested the exhausts without the silencers installed for maximum performance gain.

The xB factory exhaust system has only one connecting flange between the header outlet and the muffler, and that flange is at the rear of the vehicle, just in front of the rear suspension setup. Because installing a true cat-back system involves permanently modifying the factory exhaust, some manufacturers have chosen to offer an axle-back solution that bolts to the single existing factory flange.

For ease of testing, we tested the axle-back systems fi rst, then cut the pipe at the required location for the full cat-back systems (which happened to be the same point for all three systems tested), and fi nally completed the testing. The order that we tested the particular systems was dictated by their physical position in which they were stacked for us in the dyno area.

SO EXACTLY WHAT HAPPENED? Generally speaking, the two types of exhaust systems performed in the same manner. That is, the axle-back units showed negligible results, and the full cat-back units showed moderate gains in the mid-to-mid/high powerband while all tapering off at the peak point to best the factory exhaust by +1 to +2 WHP.

Looking at the graphs and the specific power outputs of each type of exhaust, we would like to say that the ultimate restrictor in the exhaust system is the area on the OE exhaust normally called the "b-pipe." It appears that once this section is replaced with larger diameter piping, larger and more consistent power gains are realized on this platform.

Again, we would like to say that with some level of certainty, but we can't because that hypothesis is not feasibly testable. Sure, it may seem like a simple matter of getting a larger diameter test pipe and placing a flange at the muffler end similar in design to the factory unit, so that all exhausts can be bolted to the same point and "breathe" through the same piping, but that assumes that each manufacturer would run that specific diameter pipe, following those specific bends, and terminating to a small diameter reduction just before the muffler flange. Don't believe us? Each of the full cat-back systems had their own specific bends, junctions, and pipe routing. That's not an assumption that we are willing or able to make for the sake of attempting to be fair.

So, at the conclusion of every LAB installment, we are always asked, "Who won?" And, without fail, we always answer - you tell us. A more expensive exhaust might perform the same a cheaper exhaust, but have better fi t and construction characteristics. Other times, sound output is of the utmost concern, even to the point of sacrifi cing power gains. Which exhaust won? As always, it depends on which exhaust best fi ts your need, whatever that need may be.