Hi I am new here so forgive me if I am repeating something that has already been said. A site called Spencer Low Racing has all kinds of bolt on performance upgrades. One package for the xterra includes a new cam, lifters, headers, cat back exhaust and intake. The combined gain in horsepower is said to make the horsepower 220 and torque 237 ft. lbs (http://www.spencerlowracing.com/technotes/technotes_dynoresults.html)