On the other hand, the LS9's evolution included a softer touch, specifically when it came to the camshaft, which is less aggressive than the LS7's. "According to Uncle Sam," observed Guard, "it's gotta be a refined beast, not just a beast." And this man knows that of which he speaks, since he's been working above and beyond the call of duty by field testing (ie, daily driving) one of the preproduction ZR1s. Of course, one of the most compelling things is that we're talking about 638 hp in a 3,350-pound vehicle. On the other hand, "It's equally impressive around town," Guard reported. "The availability of torque it's there when you want it." We suspect that's a massive understatement.
We asked Guard if the LS9 is able to handle more than the 10.5 psi boost it runs from the factory; he agreed that it was a reasonable theory that some ZR1 owners will be tempted to underdrive the pulley and run more boost. "We didn't probe that," he admitted. "There would probably be some risk there." But that statement belies the mission behind this powerplant: Go get as much power as possible while remaining emissions legal. The team looked at every last part in pursuit of this goal, and Guard concluded that, "We know what we have, and it's very robust." The journey through GM's extensive race track and dyno validation protocols happened-and this is a word engineers seem to appreciate-uneventfully. "We didn't hold anything back, and got where we needed to be," summed up Guard.
Now for the not-so good news, at least for those of you who want to lay hands on GM's ultimate small-block apart from its ber-Vette platform. The Wixom Performance Build Center exists to build engines like this with no-compromise, meticulous attention, and the 25 builders there can produce 45 LS9s per week. It sounds like a lot, but there's already a waiting list for the ZR1, and dealers have more than enough customers to fill their allocation. "I don't think we'll have any trouble getting rid of them," quipped Guard. Given the ZR1's performance numbers-0-60 mph in 3.4 seconds, 0-100 mph in 7 seconds, and the quarter in a smokin' 11.3 at 131 mph-we don't have any doubt of that.
Here's the inside scoop on the most exotic domestic engine going.
 The build process relies a...  The build process relies a lot on computers, but the builders still use old-school methods like marking all the caps with orange paint (this is done even though the caps are stamped) and this ergonomically designed tool that's made to pop the main caps off. Speaking of the main caps, they're the same as those found in the LS7. The '09 6.2L block, on the other hand, is 20 percent stronger than the '08 version, mainly due to increased bulkhead strength, and can handle 100-plus horsepower per liter. |  At this point, the cam has...  At this point, the cam has been installed in the block. The LS9 cam is actually less aggressive than the LS7's. "With a charged engine forcing air in, you can run a little less cam," explained Guard. "Whenever you can make combustion more efficient in non-boosted situations, the base calibration is better." The block is similar to the LS3 block (6.2L) with the addition of oil squirters. These squirters direct cooling oil at the underside of the pistons, and are critical to helping the LS9 handle the increased temperatures that come with supercharging. The LS9 block is also deck plate bored and honed. |  GM goes to great measures...  GM goes to great measures to make the assembly safer and more ergonomic for the builders at the Wixom facility. Most of us just lift a crank and set it into place-the Performance Build Center has a specialized hoist to move the LS9's forged steel crank up and into the block. Given that these guys do this all day, every day, it's probably a good idea. |