Obviously, cylinder heads are a major factor in any engine package, but it is an unusual circumstance for the very designer of the cylinder head to also play the role of the engine builder. Under development at AFR at the time this project was initiated was an all-new LS cylinder head from AFR, the AFR 215 LSx. In fact, the head was being specifically designed for 400-inch LS engines for high-output street applications, where the added displacement of the popular LS2 strokers could use the increased port volume the new head delivers as compared to the 205cc version. With a perfectly targeted cylinder head in the works, the final build was put on hold until the 225 was put into production. These cylinder heads are manufactured with the goal of maximizing flow while preserving port velocity, and with 320 cfm raging through just 215cc of intake port at only .600-inch lift, the efficiency is all there to provide huge torque and still make the power up top. Like all of AFR's modern cylinder heads, the 215 LSx is set up with components that are lightweight and functional while proven reliable in high-rpm applications, including the combination of valves, springs, retainers, and locks.

Topping the cylinder heads is a FAST 92 intake manifold, which was fully ported by Mamo. For street use, a factory LS2 throttle-by-wire throttle body was also prepped by Mamo with the full porting treatment, but for dyno testing purposes, the engine was equipped with a 90mm Nick Williams mechanical-linkage throttle body. The engine assembly was finished off with the American Racing 1.875-inch primary, 3-inch merge collector headers that run in the car.

Proving The Point To evaluate the effort, the completed engine was taken to Westech Performance Group's dyno test facility for the power numbers. Now, let's consider the circumstances. The previous LS7-style combination was pulled and sold off in parts to make way for this new engine at essentially the same displacement in the hope of better performance; you'd better believe that the heat was on as far as delivering the goods. Anticipation was pretty high as the engine was fired and taken through the break-in procedure. The well-established dyno protocols and procedures were carefully followed by the Westech crew in setting the base calibrations to the fuel and ignition systems prior to making the full dyno runs. There was no questioning the engine was exhibiting tamer characteristics than the old combination, as it idled on the dyno with a mild lope and 12 inches of vacuum. The promise of driveability seemed to be there.

It wasn't until the handle was pulled on full dyno sweeps that we had a complete picture of just how well this engine performs. A fat torque curve was one of the build criteria, but the graph showed that this engine was downright obese, pulling over 500 lb-ft from 3,900-6,400 rpm, while peaking at 564 lb-ft from 4,900-5,200 rpm. Along with the huge torque numbers, the engine was an animal, as the tach swung to the high side of 6,000, recording a peak power reading of 618 hp at 6,300 rpm, and continuing to pull with enthusiasm past peak to 6,800 rpm. As the numbers indicated, the engine certainly met their mark, and then some.

While the engine dyno numbers validated the effort, as a final note, the engine has been installed in the Z06, and it delivers exactly as intended. According to follow-up chassis dyno numbers, the new combination belts out a staggering 80 lb-ft advantage compared to the old engine, and as noted earlier, it has over 50 more horsepower at the top. Smith says the difference in the car feels like going from a small-block to a 454, with torque that comes on right now, but with power that keeps pulling as long as you've got the nerve to peg the throttle to the wall.