Q: Greg, I know by 1971 that Detroit had to follow government rules and begin using unleaded gas in their street cars. However, there were still a few high performance cars I remember, especially the 1971 Corvette with an LS6 V8 that still put out big horsepower. Any information would be appreciated. Thanks, Gary V., retired in Massachusetts.
A: Gary, the car you speak of is the very rare 1971 Corvette LS6 454 cubic inch V8 with 425 horsepower. It was similar to the LS7 engine that could be ordered from the factory as a crate motor (I bought one for my race car in 1979 for $1,448), and came with a solid lifter camshaft. However, to make sure there was no “ping” or engine destroying pre-ignition because of the unleaded, lower octane fuel, Chevy was forced to utilize just 9 to 1 compression pistons instead of higher compression pistons.
The cylinder heads were still the great breathing 2.19 intake and 1.88 exhaust design, although instead of a closed chamber format these were open chamber heads, which helped reduce the compression and thus the horsepower. My LS7 crate engine, with an 11 to 1 compression, developed an easy 465 horses, while the LS6 1971 Corvette engine produced the aforementioned 425 horses.
The transmission in the 1971 Vette was an M22 “Rock Crusher” Muncie, similar to the one I had in my 1968 Camaro SS/RS 396-375. It was way more “whiney” than the M21, but had much better gears for long lasting, high performance durability. The carburetor was also the same as my Camaro, an 800 CFM Holley double pumper, although the intake manifold was a low profile unit which hampered horsepower. By 1972, the LS6 454 was no longer available, and the days of the ultra horsepower Corvette ended. Available was a 454 LS5 with hydraulic cam and low compression, resulting in a net horsepower of 270.
Only 188 1971 LS6 425 horse examples were ever built by Chevrolet, making this Corvette one of the most rare editions of all. I located a beautiful restored 1971 LS6 that sold for $179,000 at Atlanta’s “Buyavette.net,” known as one of the southeast United State’s top Corvette collector dealers and in business for 22 years.
Thanks for your question Gary and thanks also to Tony Smith at Buyavette.net, the latter with many Corvettes in stock for way less than $179,000.