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C4 Corvettes
were built from 1984 through 1996. In 1990, Chevrolet introduced the Corvette ZR-1 with the new DOHC LT5 engine. GM canceled the ZR-1 option at the end of model year 1995 after a total of 6939 had been produced.

LT5 Engine
Known as the Heart of the Beast the LT5 is an all-aluminum 5.7 liter (349 cu in) small-block V8, thoroughly different from other Chevrolet 350 engines. The bore and stroke are both different at 3.9 by 3.66 in (99 by 93 mm) instead of the usual 4 by 3.48 in (102 by 88 mm) and features 32-valve DOHC heads rather than the usual Chevrolet 16-Valve OHV Heads. Designed by Lotus Engineering in the United Kingdom the LT5 was hand built by specialty engine builder, Mercury Marine in Stillwater, Oklahoma. The preproduction LT5 initially produced 385 horsepower (287 kW), but was reduced to 375 horsepower (280 kW) and 370 lb·ft (502 N·m) for the 1990-1992 Corvette ZR-1. The power ratings jumped to 405 horsepower (302 kW) and 385 lb·ft (522 N·m) from 1993 until its final year in 1995, thanks to cam timing changes and improvements to the engine porting. 1993 also added 4-bolt main bearing caps and an exhaust gas recirculation system. The engine was used only in ZR-1 Corvettes.

A second generation of the LT5 was in the testing phase as early as 1993. What little information that survived showed that it would have utilized a dual plenum system similar to the first generation Dodge Viper as well as variable valve timing. The next generation LT5 was set to produce between 450 horsepower (340 kW) and 475 horsepower (354 kW). Unfortunately, the cost to produce the LT5 along with its weight, dimensions (would not fit the C5 pilot cars without extensive modifications) and internal GM politics over using an engine not designed and built in house killed the LT5 after six years of production.

RPO-C60 (Regular Production Option) is the code for Manual Air Conditioning Controls. Of the 23,646 Corvettes manufactured in 1990, 3049 were built with the RPO-ZR1 (Special Performance Package) that included virtually all Corvette options with the exception of two: RPO-C2L (Dual Roof Panels) and RPO-C68 (Electronic Air Conditioning Control). After 1990 RPO-C60 (Manual A/C) was no longer available in the ZR-1.

A total of 124 ZR-1's were built with Manual A/C (RPO-C60) making them somewhat rare. The final ZR-1 built with RPO-C60 was VIN #2957.