1999 Chevrolet Corvette - Thunder Road

With an 8.1 Liter Big-Block for Propulsion, Every Drive In This C5 Is a Run Down...

Bob Wallace Mar 1, 2002 0 Comment(s)
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Some people are never satisfied. These sorts of people would probably get tired of having Wolfgang Puck for a personal chef, Nicole Kidman for a girlfriend, or a C5 convertible for an everyday driver. In some respects I can relate to that; my personal credo is "wretched excess is barely adequate." However, thinking large is one thing, living large is something else. It's like going from the Triple A minors to the Big Leagues of extremism.

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Most people find a C5 to be an impressive sports/grand touring car as delivered. Add an exhaust, a higher flow induction setup, maybe some custom wheels and stickier-than-runflats rubber and it's close to perfect. The more outr elements will congregate around the Z06-it's hard to beat that extra 40 to 55 horsepower (depending on which years of Z06 and C5 we're comparing), plus recalibrated and substantially better suspension, bigger and much grippier tires-more than adequate for almost everyone, but...

There's still that lunatic fringe. We know of one SoCal extremist who is currently putting the wraps on his seven-liter (!) '02 Z06. Katech is now offering a 585hp street version of the 7.0L race engines they build for the C5-Rs. Then there's San Diego, California's Larry Hofer and his personal vision of Big League extremism-an 8.1 liter (that's 496 cubic-inches for the metrically-challenged), big-block-powered '99 convertible. Looks like extremism just got ratcheted up a notch or two.

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There's no way to disguise the Vortec 8100's cut-apart and re-configured intake manifold so that it looks like a factory-issue LS1, but by utilizing the LS1's plastic fuel rail covers, a semi-stock look is maintained.

If Larry's moniker or this trait of shoehorning big-blocks into late-model Vettes sounds familiar, it's because one of his earlier endeavors, a Rat-motored C4, found its way onto the pages of VETTE about four years ago. And like that prior escapade, the work was done almost entirety at Hofer's business, fittingly (but not especially creatively) named The Corvette Shop.

This latest bout of madness began in June of 2000 when Hofer bought a slightly used '99 C5 from a customer. The ragtop packed an MN6 six-speed, was painted Navy Blue Metallic, and trimmed with a Light Oak interior and soft top. A nice, elegant combination. It proved to be, in Larry's words, "a very nice driver, very quiet, smooth, and would go quick as long as you buzzed the engine." The downside, at least from this extremist's perspective, was, "the lack of acceleration in fifth and sixth gears. No torque. After driving a C4 with 500hp and 450 lb-ft of torque for several years, the C5 was boring."

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The Light Oak interior is all stock, in keeping with this car's "sleeper" persona.

Then, through a friend, Larry heard about a new derivative of the venerable big-blocks that dated back to 1965, an 8.1 liter monster that was destined to be a 2001 offering in Chevy Silverado and GMC Sierra heavy-duty pickups and medium-duty trucks. In their 2001 model year Powertrain press releases, GM described the Vortec 8100 V-8 as "a new, highly refined big-block V-8...the legendary GM big-block for the new millenium." Hofer saw the same sort of individual coil-near-spark-plug ignition setup as on the LS1, meaning some sort of crank or cam sensor for igniting the fuel and air charges, and thus the possibility of computer compatibility-a major, perhaps insurmountable, problem with a conventional 454 or a 502 like Performance Parts markets in several forms. As a result, he saw the potential of swapping one of these torque monsters into his C5.

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There was a time when small- and big-block Chevy V-8s could be swapped back and forth without a major hassle. The advent of the C5 and its GEN III (LS1) engine's totally new architecture means that nothing new goes where something old once resided, and that a mountain motor intended for a large pickup ain't gonna fit, at least without a LOT of work, within a C5's engine bay. Larry took a leap of faith and ordered a brand new Vortec 8100 from The General.

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The 8.1L Vortec 8100 V-8, as delivered...

Upon its arrival at his shop, Hofer started off by doing a point-by-point check of parts interchangeability between a traditional big-block and the Vortec. Guess what-the valve covers are about the only thing. Among the differences in the Vortec are the cast-aluminum oil pan, different motor mount pads, LT1-style cooling (reverse flow, coolant in and out of the front of the block), cam and crank sensors machined into the block, and the list goes on. To make the beast fit where an LS1 once lived, the front drive had to be shortened a full 4 inches, and to do this meant a new hub for the crankshaft, setup for an LT1 damper and pulley, custom accessory brackets to hang the power steering pump, A/C compressor, and alternator, and an entirely new, ZR-1-influenced water pump and thermostat assembly built around a Meziere electric water pump. At least all of the LS1's sensors fit.

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...and, less accessories and intake, being adapted to the C5's aluminum front suspension and engine cradle.

Larry did a comparison, based on crankshaft centerlines, between the LS1 and the Vortec 8100. Opportunities for creative solutions (calling them "problems" sounds so negative) included an oil pan that was too low, an intake manifold that was too high, and a flywheel that was too far aft. Both the intake manifold and the oil pan were treated to extended cut, weld, and re-configure sessions in Larry's shop, with the pan needing a custom windage ray, pump pick up, and drain plug boss. A one-off flywheel was made to spec, set up to work with a Z06 disc and plate. And the C5's steering rack had to be relocated 1 1/2 inches forward.

Ultimately (and obviously), everything came together. The C5's ECM (computer) and the Vortec 8100 V-8 are compatible-once the right injectors were determined. The 8.1 comes with 46 lb/hr gushers while an LS1 has 26 pounders. It ran way too rich on the 8.1L's nozzles, and after much trial and error, Hofer found the LS1 injectors are not only completely adequate for the mega motor but it also runs perfectly on them.

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It also runs plenty cool-no overheating problems even in the peak heat of a Southern California summer. The stock six-speed transaxle and differential have proven to be up to the task so far, and the big-block's extra tonnage is controlled by a combination of Bilstein coilovers at all four corners, and Z06 stabilizer bars fore and aft. Custom headers were an absolute necessity, but the balance of the exhaust system is a blend of factory and a B&B stainless steel cat-back system. Hofer's hauler looks amazingly normal, with custom wheels, an RKSport rear spoiler, and Z06 rear brake vents its only external changes.

What is likely the world's only 8.1 liter C5 Corvette looks, sounds, and even drives like a normal fifth-gen-until Larry mashes the loud pedal and that extra 100-plus lb-ft of torque provides an explosive thrust forward. When we asked Larry Hofer if he was happy with his creation, he simply said, "I'm still amazed!"

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