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Chevrolet Corvette ZR1 LS9 Engine Specifications - Domestic Exotica
An Inside Look At The Conception & Construction Of GM's Startlingly Powerful New LS9
Nov 1, 2008
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Chevrolet Corvette ZR1 LS9 Engine Specifications - Domestic Exotica
Giant leap forward that it is, an amazing 76 percent of LS9 parts are already existing GM components. There were about 100 new parts developed, with 25 percent of these being common to other small-blocks.
The Performance Build Center in Wixom, Michigan, specializes in producing low-volume engines for GM's premier vehicles with a combination of personal attention and technological prowess. The 38 employees at the plant, 25 of whom are skilled builders, can produce 45 LS9s a week. The process starts here, with these just-delivered blocks and cranks. They're supposed to be clean upon arrival, but GM Powertrain pressure-washes them again just to make sure. Each builder carefully examines his block before assembly begins, and can reject it if he finds something he doesn't like.
Each engine build is accomplished by proceeding though multiple stations, and the parts needed at each station are set up in kitting trays. These trays are color-coded (green indicates LS9) and contain all the components needed at that post. This way the builder can make sure he has all the needed parts and can be sure not to forget to use any.
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 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 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.
This device is specific to the LS9 assembly process, and is used to guide the rod into the engine. Besides making sure the rod end doesn't injure the bore or crank journal, it also ensures the rod doesn't damage the oil squirter...
...The reciprocating assembly is strong and lightweight, consisting of titanium rods, along with forged aluminum, friction-coated pistons.
The LS9 also features this new integrated oil cooler to help deal with the supercharged engine's greater oil system demands; in fact, the dry sump system capacity was increased and its scavenging ability improved as part of the package. The increased pressures involved with forced induction meant that even items as innocuous as the oil filter needed to be strengthened, so this new ACDelco oil filter-which should fit any LS engine-has an extra-thick canister to resist bulging.
Each station is configured to carry out a specific task, and only the tools needed for that task are on hand. The task sheets are color-coded green for LS9 and white for LS7 engines. See the screen with the green happy face? This is one of the three check stations found throughout the build. If a step is skipped, the face will be red and sad until the situation is remedied. Also notice the white templates-they show which order the bolts need to be torqued in. Before the builder can torque down any bolt he must first scan the appropriate bar code for that set of bolts. This sets the torque wrench to the proper setting and prevents errors, since the system won't let the builder scan the next fastener until the previous has been scanned and torqued.
As you might expect, GM has a number of specialized tools for assembling engines. There's an alignment tool to make sure the timing cover is dead center to the crank, and this plate ensures that the bottom is flush to the block to ensure a leak-free seal to the oil pan. Also visible is the LS9's higher-capacity oil pump, installed to ensure adequate oil pressure at the high-cornering loads the ZR1 is capable of.
One critical issue, of course, was increased stress placed on the top end; the LS9 has to deal with a 30 percent increase in cylinder pressure created by the forced induction setup. "The pressure is literally trying to lift the head off the block," explained Guard. The team developed a new gasket with four active layers for the LS9. "We needed more 'spring,'" Guard said. Each layer allows for 5 microns of movement, which covers the 18-20 microns of movement that were needed under this pressure. Final validation testing with the gasket, Guard said, was "perfectly uneventful."
The cylinder head bolt size was increased from 11 mm to 12 mm, a step that was needed "just to hold the head on," said Guard. At Wixom, this literally over-the-top tool torques down all 15 head bolts in one single operation. It takes less than five minutes to install a head in this manner, making it extremely efficient.
The head bolt torque operation is of course carefully monitored. If any bolt reads outside the required torque spec, a red or yellow light indicates which one needs further attention. The computer also records this data-both torque and angle-and keys it to the serial number of the engine for future reference.
Showing a further refinement upon the LS7 platform, the LS9 uses rails beneath the rockers to help improve valvetrain control at high rpm. The heads themselves, on the other hand, aren't as exotic, but are certainly effective. They're designed specifically for the LS9, but are close cousins of the LS3 and L92 heads. The rotacast LS9 heads have winglike shapes cast into the intake runners to induce swirl and improve the mixture motion of the pressurized air/fuel charge.
Even in this high-tech facility, lots of good, old-fashioned marking paint is used throughout the process. After the blower is installed, the builder marks the back of the unit to show that the protective plastic cover was removed. Usually it's just a dot, but we used an X this time. So if you're lucky enough to own a ZR1, check your blower. If you see this mark, then this is your engine.
Force-feeding duties on the LS9 are performed by a sixth-generation-design R2300 supercarger from Eaton, with a Corvette-specific case design. The four-lobe rotor design, which also features an abradable powdercoating, promotes quieter and more efficient performance. The unit displaces 2.3 liters to ensure ample air volume at high rpm. Maximum boost pressure is 10.5 psi, a level that gets the most out of the engine while ensuring reliability.
The LS9 employs a center-feed fuel line system to ensure even fuel flow between cylinders (each fed by a high-capacity 48 lb-hr fuel injector) while creating less noise. More importantly, the powertrain team developed a dual-pressure fuel arrangement. The system operates at 250 kPa during idle and low-speed operation to enhance drivability, but then cranks up to 600 kPa to meet the requirements of higher speed and WOT conditions.
With the blower installed and torqued down, the charge air cooler is then installed. The LS9 employs a liquid-to-air charge cooling system; inlet air temperature is reduced by up to 140 degrees F for a denser intake charge. The design of the supercharger case and the integrated charge cooling system were dictated by the space and dimensions under the Corvette's hood. To that end, the charge cooler was designed as a dual-brick system, with a pair of low-profile heat exchangers mounted longitudinally on either side of the supercharger. It's only slightly taller than the non-supercharged 6.2L engine.
The GM Performance Build Center's motto is "One Builder for One Engine," so you can be certain that every builder takes his job very seriously, and even more so since his name goes onto the side of the blower. And of course GM has a template to make sure the builder gets his nameplate in just the right spot.
Once the supercharger assembly is installed, the engine is sealed and pressure-tested. Air is forced into the oil and water passages, and the computer makes sure there are no leaks. If the pressure isn't held, the builder pinpoints the location of the leak before the engine can move on.
The LS9 uses the same exhaust manifolds as the LS7. These pieces are trick, fabricated from 18 separate parts, and very efficient. "One of the last parts designed for the LS7 was the manifold," our man Guard told us. "The team did an excellent job to get it to crack 500 hp." When it came to the LS9, Guard said it did not provide "a significant cork."
The LS9's flywheel is put on using a two-pass system-each is marked with paint on the final pass to show it is finished. Note that the flywheel is attached to the crank flange with nine bolts instead of the usual six, providing greater clamping strength.
Speaking of greater clamping strength, the LS9's dual 260mm disc clutch spreads the engine's torque load over a wider area to provide just that while maintaining easy clutch pedal effort. The assembly itself is much heavier than the LS7 clutch, so GM uses an air-assisted lift to help the builder put it in place for alignment and final installation.
The last step in the assembly is weighing the engine. Because the LS9 doesn't have a dipstick, the oil is later added by weight, making it important to know what the engine weighs dry-529.8 pounds in this case.
Each assembled engine is first run on natural gas so it can be externally balanced. After that it's put though a 45-minute cold test run by a DC motor. When the engines are complete, they are double checked and sent offsite for a 20-minute hot test and dyno validation. It takes from 4.5 to 5 hours to build an LS9 at Wixom, which means it can churn out around 45 units a week. We'd all like to see LS9s available as crate engines, but for now, every one is bound for a ZR1-and there's no shortage of willing buyers.
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