The Jeep inline-six has the dubious notoriety of being the last engine
built for an emissions-controlled vehicle with a flat-tappet cam.
Roller cams offer faster and potentially more valve opening which
translates into power by getting more air and fuel into the combustion
chamber. The roller lifter also reduces friction, which can free up
even more power. Finally we can get a roller cam for our '91 and up
4.0L engine. The company claims up to a 50hp increase over stock,
depending on additional modifications. Information: 505 Performance,