INFORMATION
C4 Corvettes (4th generation) were built from 1984 through 1996 and in 1990, Chevrolet released the Corvette ZR-1 with the radical overhead cam LT5 engine that shared only the 4.4 inch bore spacing with previous LT engines. The LT5 was engineered by Lotus Engineering in the United Kingdom headed by design manager David Whitehead. The engine was produced and assembled by Mercury Marine in Stillwater, Oklahoma headed by Project Engineer Terry D. Stinson.

The LT5 was an all-aluminum 5.7 liter (349 cu in) small-block V8, but was thoroughly different from any of the other Chevrolet 350 engines. The bore and stroke were 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 it featured Lotus-designed 32-valve DOHC heads rather than the usual Chevrolet 16-Valve OHV Heads. It 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 duel 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 that was not designed and built in house killed the LT5 after six years of production.

GM canceled the ZR-1 option at the end of model year 1995 after a total of 6939 had been produced. The LT5 however wasn't an evolutionary dead end. Despite being discontinued, a new class of premium V8s for Cadillac and eventually Oldsmobile, the dual overhead cam V8 Northstar and its derivatives, drew heavily from the LT5's design and lessons learned from its production. GM also took lessons learned from producing a completely aluminum engine and applied them to the new LS series of engines.

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-C68 was no longer an option but was included in the Special Performance Package.

In 1990 only 124 ZR-1's were ordered without RPO-C68 (i.e. they were equipped with RPO-C60, Manual A/C) making them somewhat rare. The final ZR-1 built with RPO-C60 was VIN #2957.

If you own a 1990 ZR-1 with RPO-C60 and wish to have it featured in this album, please contact me for details.