Volume II, Issue 12, Page 23

We’d wanted to be first out with this but the maniacs at Jalopnik, Autoblog, and a sheaf of other sites had it posted when the embargo ended a minute after midnight. What to do? Wait until the mid-month update to lay it all out after the initial rush had cooled, this time with numbers and explanations not included in the original press release material, maybe we’d even appear responsible and talk to an engineer or two. Our grand plan was nearly squelched by the ever-lovin’ holidays. Come the end of December, most of Detroit turns off the lights and blows town for a week. Let’s see how we did.

This engine is exclusive to the ZR1 Corvette. Obviously, it had to be more powerful than the 427ci LS7 yet comply with 50-state emissions. Rather than increase displacement and increase cam timing, the plan that usually follows includes a somewhat smaller engine (in this case the 6.2L) with an application of forced air induction as the blackjack in the back pocket. Since GM is thoroughly entrenched with the Eaton supercharger and has proven it in myriad dead-reliable applications, it only made sense to continue with positive displacement rather than turning to the turbocharger. As an aside, the Katech-built 500ci “LS7” engine in the Pratt & Miller Engineering C6RS (Bow Tie Bytes, 12/07) grew from a Dart cylinder case. The team is pushing for an all-inclusive 50-state emissions package that will be final before the car goes into production this February. Output is nearly identical to that of the LS9 but there is no power adder involved. Quite a feat, we’d say.

Since the LS9 power module is more or less been built around the supercharger, it was expected to produce high peak output numbers neatly conjoined with excellent low-speed drivability. A supercharged engine produces more heat than a normally aspirated engine so the LS9 features dished 9.1:1 forged pistons, titanium connecting rods (ala the LS7), and a forged crankshaft carrying a 3.62-inch stroke and a 9-bolt flywheel flange (instead of the 6-bolt common to the LS3). The bogey was 300hp at 3,300rpm, nearly 320lb-ft of torque at 1,000rpm and 90 percent of peak torque from 2,600 to 6,000rpm. Torque tops out at 4,000rpm while hp takes it all the way out to 6,500rpm.

The cylinder case is based on the 6.2L LS3 (4.4-inch bore spacing) but is cast from 319-T5 aluminum for its aversion to heat, has bulkheads that are 20 percent stronger than the original 6.2L block (hone over-travel radius changed from 3 to 10mm), 6-bolt, dowel-aligned, forged steel main bearing caps, eight block-mounted oil squirters, and cast-iron liners measuring 4.06-inches diameter that are honed with a deck plate. The crankshaft damper has a keyway and a friction washer, also designed to support high load.

Similarity to the LS3 is also found in the LS9 cylinder head casting, made from A356T6 material and cast in an unconventional manner to manage the heat from the supercharged engine better, particularly in the bridge area between the intake and exhaust valves. Cam timing is milder than that of the LS7 and consistent with a supercharger application. Cam gear, including roller lifters, 1.7:1 ratio rocker arms (intake side is offset), and valve springs (294.5 pounds open, 89.9 pounds closed) is all LS3 and finished off with LS7 retainers. As a reference, the GM ASA Hot Cam (0.525/0.525) is somewhat bumptious and idle quality is good at 800 rpm. The LS9 cam has a higher lift (0.555/0.555-inch) and carries 230/211 degrees of duration at 0.050-inch.

The Eaton R2300 blower is sixth-Gen iteration with a case specific to the LS9 application and its new four-lobe rotor design is meant to promote quietness and efficiency. A large 2.3L case ensures that the motor won’t run out of air at high engine speed. Pressurizing the intake charge invariably includes a wrapper of heat, so a liquid-to-air charge cooling system (a dual brick arrangement located directly on top of the supercharger housing) drastically reduces inlet air temperature.

The best part of all this? GM and other manufacturers typically rate official output lower than it really is--a hangover from the musclecar days. If the engine in the spooky Blue Devil doesn’t make at least 650 horsepower, we’ll eat our hat, and maybe yours, too. Yeah, any ol’ habanero juice will do.   

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