Corvette Prints on Parchment| 1990 ZR1 Engine Corvette Illustrated Series No.83

Not since the glory days of the 1967 to 1969 427/435 engine, had there been such an impressive sight as the LT5 engine. Corvette designers knew that they would need a very special engine to put the car into world-class territory. To expedite the process, Chevrolet established the parameters and had Lotus complete the details of the new engine design. Assembly of the racer-like engine was subcontracted to boat engine maker, Mercury Marine of Stillwater, Oklahoma.

The Mercury Marine 21,000 square foot facility used state-of-the-art machine tools with extraordinary tolerance capabilities. After the block and heads were machined, they were examined with a Cordax measuring machine that checked every three-dimentional measurement in only 45 minutes. Next was a six-step assembly process.

First, the heavily ribbed short-block was assembled with aluminum cylinder sleeves coated with Nikasil, a nickle-silicon alloy. The crankshaft and connecting rods were forged steel, and the pistons were aluminum. The five main bearings were held in place with an aluminum cradle that attached with 28 bolts. Next, the double-overhead-valve aluminum heads were assembled. Each bank had two camshafts, one for the intake valves, and the other for the exhaust valves. The valve stems were actuated directly off the cam lobes.

During the third step, the assembled heads, valve train, and cam covers were installed. The fourth and final assembly step saw the installation of the ignition hardware, alternator, the complete induction system, and other accessories. The electrical system was then computer checked, followed by a dyno test. The completed engine had a 14-minute dyno test for initial startup, break in schedules, and a full-throttle run to establish power rating.

The new LT5 engine measured 350 cubic-inches, and was rated at 375 net horsepower. Aside from the details, there are several other very unique aspect of this engine. Not only was it a nearly completely hand-made engine, but the LT5 was the only official Corvette engine that was not built by Chevrolet. Measured the old way, the "gross" power was close to 500!

In March of 1990, with a nearly stock ZR-1, Tommy Morrison showed off the LT5's capability by setting several speed records. His 5,000-mile average speed was 173,791 mph. His 12-hour record speed was 175.573 mph, and his 24-hour record speed was 175.885 mph. These record had previously been held by for over 50 years by Abner Jenkins and his V-12, 1,570 horsepower aircraft engine powered racer. The new production ZR-1 had plenty of grunt to set speed records and run with anything on the road.

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