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427 Engine "Mystery Motor"

427 Engine "Mystery Motor"

427 Engine Mystery Motor

Last month we had some fun and rekindled fond memories with 327 Day, so this month we are declaring Sunday to be 427 Day! What better excuse to get your Corvette out this weekend and drive than to honor this iconic Chevrolet engine!

Development of the 427 big-block started with the so-called “Mystery Motor” used in Junior Johnson’s 1963 Daytona 500 record-setting Impala Super Sport stock car. This "secret" engine was a substantially modified form of the previous W-series 409 engine, and was subsequently released for production use in mid-1965 as the Mark IV, referred to in sales literature as the "Turbo-Jet V8." Playing off the popularity of its 327 little brother the “Mighty Mouse,” the 427 soon became known to automotive journalists and enthusiasts simply as the “Rat.”

The 427 was introduced as an engine option at the beginning of 1966 Corvette production. A variety of single and multi carburetor options, camshaft, cylinder head, intake, and compression ratio combinations would yield 7 unique 427 engine packages:

The 327 engine as seen in the 1964 World's Fair Corvette
The 1969 427-430hp L88 engine
First Year Last Year Engine Code Features Compression
Factory Gross Power Rating
1966 1969 L36 4-barrel 10.25:1 390hp
1966 1969 L72 4-barrel + solid lifters, more aggressive cam and high flow cylinder heads 11.00:1 425hp
1967 1969 L68 L36 with 3x2-barrel carbs. 10.25:1 400hp
1967 1969 L71 L72 with 3x2 barrel carbs. 11.00:1 435hp
1967 1969 L89 L71 + aluminum heads; RPO L89 also applied to L78
"375 HP" 396 engine with aluminum head option.
11.00:1 435hp
1967 1969 L88 Racing-spec cam, high-flow aluminum heads (casting #s varied by model year) and some upgraded, competition-grade parts 12.50:1 430hp
1969 1969 ZL1 Aluminum block with open chamber "3946074" aluminum heads; cam even "hotter" than L88's; upgraded parts similar to L88's 12:00:1 430hp

Like the “Mouse” small block, the 427’s rugged dependability and performance ensured an extensive role in Chevrolet and GMC Commercial vehicles, in addition to numerous marine applications. Super Chevy Magazine even named 3 variants of 427 as the number 7, 8 and 9 best engines ever made by Chevrolet!

History repeats itself in 2006, as the LS7 505HP 427 was called upon to propel the 6th Generation Corvette Z06 model. Although the LS7 427 is a small block variant sharing very little with its 1960s big block ancestor, it proudly carries the Corvette 427 flag in the new century.

Data and stories about the Chevy 427 could fill volumes, but not here. Any fan of the “Rat” can take it from here with your own stories and memories.