Since the introduction of GM's famed L92 head it seems LS1 enthusiasts have been foaming at the mouth for a small-bore version that will accommodate the LS1/LS6's 3.89-inch cylinder. Unfortunately, the mammoth 2.165- and 1.59-inch valves simply won't fit, which meant a considerable redesign would be necessary. Enter Mast Motorsports. In the midst of developing a high-flowing 12-degree version of the popular L92/LS3 head that would significantly improve upon the square port's already impressive design, Mast decided it would like to cover all its bases with large- and small-bore versions (in addition to medium-bore). Mast's forward-thinking nature, you may remember, extends back several years when they jumped on the L92 bandwagon before anyone else knew how to spell variable valve timing. By 2009 Mast's core of freewheeling Texas A&M grads realized that it would be impossible to eke any more horsepower out of their VVT and other LS combos without a higher-flowing square port replacement for the stock heads.
Now some of you may be wondering whether a cathedral or rectangular port is better, and some of you may have already made up your minds, but officially the jury is still out. Both have excellent attributes and have each proven quite formidable on the dyno and at the track. Rather than debate what seems to be a futile and endless argument we chose to simply bolt down Mast's new heads and insert a matching cam into an otherwise stock LS1. Horace Mast, owner and engineer for MM, sent us a custom spec 226/240-duration roller to maximize the heads. Meanwhile, a GM L76 intake manifold, FAST 90mm throttle body, FAST injector adapters, and SLP throttle cable conversion bracket would replace the stock LS1 intake setup. Though this does add some cost to the overall install, consider the price of a high-flowing aftermarket intake manifold (that doesn't come with fuel rails, 42 lb/hr injectors, and an electronic throttle) and you will see that you are still coming out ahead (pardon the pun).
To test out this bad boy we went to none other than Race Krafters Automotive Machine in Lancaster, Pennsylvania. This little engine shop has quietly been building some very impressive late-model GM EFI motors in addition to its usual squadron of serious NHRA racers and the like. In fact, they often do work for the notorious Bill "Grumpy" Jenkins, including tune his 2004 GTO daily driver. RK President Bob Wise has piloted some very impressive single-digit race cars, but he takes great pride in his 2001 Z28 street car, which had previously been well into the 11s with little more than an NOS nitrous system, Corsa catback exhaust, airlid, RPM 4L60E trans, Vigilante converter, and a set of drag radials. A 9-inch rear with 3.73s and ARH long-tube headers have also found their way onto his Camaro lately, so it was ripe for a set of high-flowing heads and a lumpy cam.
*Measured on Race Krafter's SuperFlow SF-1020 with 28 inches of water.