The Corvette LT-1 engine is known as the “Mouse that roared.” A high-performance version of Chevrolet’s venerable small block, affectionately known as the “Mouse Motor,” the LT-1 engine not only roared, but when coupled with the ZR-1 heavy duty chassis option package, it transformed the road-going Corvette into a well-balanced competition sports car with enough power and handling to match anything that Europe had to offer. Much like espresso intensifies the pure essence of coffee flavor, the LT-1/ZR-1 options intensified the essence of the Corvette – the high-performance, free-revving engine and the exquisite handling of the chassis delivered pure, unadulterated driving adrenaline.
Chevrolet LT-1 engine
Many consider the LT-1 V8 the best small block engine that Chevrolet ever made, a compliment that should not be taken lightly. Over 100 million small block V8 engines were made between its introduction in 1955 and 2011. To even be considered as one of the best is a supreme compliment to its designers and builders. Author Mike Mueller, in his book Corvette 1968-1982 says of the LT-1, “In its day, it surely stood as the supreme small block Corvette.” The LT-1 was available as a Regular Production Option (RPO) in the Corvette only between 1970 and 1972, turbulent years in the automotive industry due to ever-stricter government regulations regarding safety and emissions. Following the 1972 model year, it was apparent that the engine would not meet upcoming emission standards and it was dropped from the Corvette lineup.
For 1970 the 350 cu. in. LT-1 was rated at an astounding 370 gross horsepower – only 20 horsepower less than the 454 cu. in. LS-5 big block V8. Thanks to a bevy of high-performance and heavy-duty components, such as solid valve lifters, forged aluminum pistons, four-bolt main bearing cap blocks, special high lift cam, high rise aluminum manifold, transistorized ignition, and a huge 780 cfm Holley carburetor, the LT-1 with a compression ratio of 11.0:1 produced well over one horsepower per cubic inch of displacement. A 1970 Corvette with the LT-1 could zip from 0 to 60 mph in 5.7 seconds and reach the end of the quarter mile from a standing start in 14.2 seconds. A total of 4,977 1970-1972 Corvettes were produced with the LT-1 engine, including 1,287 in 1970, 1,949 in 1971, and 1,741 in 1972.
RPO ZR-1: The rarest small block Corvette
While the LT-1 equipped Corvettes were potent cars, they were intended for street use and could be purchased with most Corvette comfort and convenience options, with the exception of air conditioning, which could not be ordered with the LT-1 in 1970 and 1971. Chevrolet saw the need for a more race track-specific Corvette for tighter or smaller race tracks where the powerful L-88 racing big block Corvettes lacked the required nimble handling, thanks to the extra weight of the big block engine over the front wheels. Somewhere in the Chevrolet hierarchy, someone had the genius idea of adding the heavy-duty racing chassis components of the big block racer to the already potent LT-1 and, voila – the ZR-1 was born.
ZR-1 was the RPO identification code for the “Special Purpose Engine Package” in which the “Special Purpose” was racing – this RPO was not intended for street use. To limit use on street Corvettes, RPO ZR-1 could not be ordered with many driver comfort features, such as air conditioning, power windows, power steering, a radio, an alarm system, a rear window defroster, or special trim items like optional wheel covers. The package included the LT-1 engine option in addition to the M22 “Rockcrusher” manual transmission, heavy-duty power brakes, a special aluminum radiator with catch tank, a seven-leaf rear spring, heavy duty shock absorbers, and front and rear sway bars. The LT-1 engines for ZR-1s were slightly modified to include lightweight flywheels and high torque starters.
Only 53 Corvettes with the ZR-1 option package were built between 1970 and 1972 – 25 in 1970, 8 in 1971, and 20 in 1972, making them the rarest of all the small block Corvettes. The ZR-1 option was priced high intentionally, to limit its casual purchase for street use. The cost of the option alone was around $1,000, to discourage buyers from placing their order without knowing its true purpose. Said author Mike Mueller, “Like the L-88, the ZR-1 was a mean and nasty chassis that could both take punishment and dish it out with the best of them.”
ZR-1: The mystery option
By now, many Corvette fans are probably wondering why they’ve never seen a ZR-1 Corvette. One reason, in addition to only 53 ever being made, is that there was no exterior or interior badging to indicate the presence of the ZR-1 option package. When Camaro offered a high-performance racing option package in the late sixties, the option (RPO Z28) was so popular that it was officially adopted as the name of the special model – over the years variously written as Z/28, Z-28, or Z28. Not so at Corvette. Corvettes with the LT-1 engine are identified only by pin striping and small “LT-1” logos on the hood bulges. Among the cognoscenti, such Corvettes are known as “LT-1s”, but the name was never adopted as the official model designation. From a visual standpoint, a ZR-1 would look pretty much the same as any other Corvette with the LT-1 engine.
Our friends at Merriam-Webster define “essence” as, “The most significant element, quality, or aspect of a thing or person.” The essence of a Corvette is its driving adrenaline or spirit, and the LT-1 engine captures and concentrates this essence much as espresso captures and concentrates the essence of coffee. The essence of the raucous, racing Corvette with the ZR-1 option, however, is more analogous to espresso with a double shot of 120 proof grappa added. Fantastico!
A big Corvette “Thank you” goes out to Terry Michaelis of Pro Team Corvette for allowing us to use the photos of Pro Team’s ZR-1.