Celebrating 4/02 with Chevy’s Secret Big Block You Should Know

Today is 4/02, and we’re kicking off our perennial set of April big block features with GM’s 402ci V8—the mill of unofficial displacement hidden in plain sight during the early 1970s. The number never appeared on a badge, instead existing as the 400 for pickups and larger Chevy models, and disguised as the 396 for most performance applications. Its presence has perplexed even those with a longstanding allegiance to the Bowtie brand, and while we won’t be able to fully untangle legend from fact here, we can at least talk a little bit about the 402 and how it came to be.

For starters, the 396 was the first of GM’s legendary Mark IV V8 series; its distinctive staggered-valve “Porcupine” heads were loosely based on those from the missing-link 427 Mark II “Mystery Motor,” though  it was its own design altogether. Let’s back up: the previous W-head 409 wasn’t cutting it on the high-speed tracks, and the prototype Mark II was introduced as a remedy. Besides its 427ci displacement, little else was disclosed to the motoring public at the time. Its wide, rectangular valve covers hinted at something relatively new below (more on that later). Even though GM’s official racing ban was already in place, the experimental mill proved its worth under the hood of five race-prepped Impalas on the steep banks of Daytona in 1963, and also found its way into a pair of Mickey Thompson-built Sting Rays.

Back to the 396. It was intended as a production engine from the start, and when it appeared in 1965, it carried over the “Mystery” V8’s most distinctive feature: canted-valve cylinder heads. The picture above shows how intake and exhaust valves were angled in varying directions that, with valve covers off, looked like the quills on a porcupine. Its 4.094 bore and 9.8-inch deck height placed the mill in big-block territory, and it arrived labeled as the Turbo-Jet V8, available in three flavors: the L78 (425 horsepower), the L37 (375 horsepower), and the L35 (325 horsepower). The numbers 3-9-6 immediately began to signify performance for contemporary musclecar buyers, and it presided under the hood of machines like the Z16 Malibu SS, Chevelle SS 396, Camaro SS, Corvette Stingray, and others.

Now, onto the 402s themselves. As emissions restrictions tightened toward the end of the musclecar era, the 396 was punched out to 402 cubic inches to take advantage of regulations stating that engines over 400 cubic inches were subject to less stringent emissions controls. One rumor, albeit a fun one, was that GM’s Tonawanda engine plant had a surplus of rusted bare blocks, and bored them out in efforts to “clean them up a bit,” creating the 402. But there’s no need for tin foil hat theories; the 402 was the 396, bored .030 over. (Although two commenters say it was actually +.031 or +.032.)

Even though the buying public had no issues with larger displacement, the 396 had earned a fearsome reputation on street and strip, so GM skipped any real effort to create a brand for the 402. In 1970, L34 and L78 V8s displacing 402 cubic inches were still billed as 396s, while those optioned under RPO LS3 were branded as the 400 or the Turbo-Jet 400 (not to be confused with the small-block Turbo-Fire 400). By 1973, the 396/402 and its famous 427 sibling had been phased out altogether, and Chevrolet’s big-block future rested on the mighty 454—but that’s a story for another day.

References: Chevelle Stuff, Mac’s City Motor Garage, Hot Rod