The competitors: On top is the factory manifold, which is somewhat tuned at least. In the middle is the Gibson GP129S stainless header that features 15/8-inch-diameter tubes. It fits 4.9L, 5.3L, 6.0L and 6.2L Gen IV V-8s in many GM truck and SUV platforms. On the bottom is the Stainless Works long-tube header, which has 13/4-inch tubes that are approximately 33 inches long. Thus far, it has been tested to fit only the 2007-09 Tahoe/Yukon applications, but it's likely to fit other Gen IV small-block applications as well, once Stainless Works get the chance to test fit them.