Found under the bonnets of everything from race cars to dump trucks and monster trucks, Chevrolet’s W-series big-block V8 range kicked off in 1958. Three years earlier, the Bowtie boys had launched their all-new 265ci small-block, but they quickly realised it didn’t have the herbs needed for the company’s upcoming truck and high-performance car models. The W-series big-blocks were their solution.

First published in the March 2025 issue of Street Machine

While it’s commonly believed that these big-blocks were nicknamed W engines for the shape of their valve covers, it was actually an internal code used by Chevy engineers. They’d started designing three versions of the new mill under W, X, and Y code names, and ultimately the W version won out.

Chevy designed the W around a heavy-duty, two-main iron block running a 74-degree angle on the deck and an angled crown on the pistons. This gave it a combustion chamber that promoted flame speed and resisted detonation, which was vital for stressed engines in the 50s.

The bore came in at 4.125in, with a 3.25in stroke, while the wedge-shaped heads had a 16-degree valve angle, and led to those iconic rocker covers. Introduced in 1958’s all-new Impala performance model, the 348ci W was 4.3cm longer, 7.6cm wider, 2cm lower, and 57kg heavier than an early small-block.

Initially sporting a single Carter AFB four-barrel carb, the 348 was rated at 250hp, but this quickly rose to 305hp, and then 320hp. By 1961, the single-carb 348 was rated at 340hp gross. It could also be optioned with triple Rochester two-barrel carbs, originally rated at 280hp, then 335hp, and finally 348hp in ’61, bringing the first iteration of W engines to a close.

Chevy’s replacement for the 348 was the now-legendary 409ci W. Running a 4.3125in bore and 3.5in stroke, a single Carter AFB four-barrel carb and solid-lifter cam, the 409 was initially rated at 360hp but was soon lifted to 380hp, while a twin Carter AFB variant came stomping in at 409hp.

The 409 powered some of the hottest Chevys of the early 60s; The Beach Boys even paid tribute to it in their 1962 song 409. By 1963, there was a base 340hp 409, a hotter 400hp version with a solid-lifter cam and single carb, and a 425hp hot dog with 11.25:1 comp, twin four-barrels and a solid-lifter bumpstick.

If you sauntered into your local Chevy dealer in 1963 and ordered your Impala SS with Regular Production Option Z11, you scored the ultimate in W motor performance: the 427ci stroker. Packing 13.5:1 comp, the 427 ran a flat-out, race-grind solid-lifter cam, two-piece aluminium intake, and twin Carter four-barrel carbs, which Chevy then down-rated to 430hp.

With their lightweight bodies and huge horsepower, Z11 Impalas were thought to have run the quarter-mile as quickly as 10.8 seconds and could hit speeds of more than 120mph.

The W series took its last bow in 1965, but Chevrolet replaced it with the legendary MkIV 396ci and 427ci big-blocks – perfectly timed for the imminent muscle car wars.

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Following the MkI W mills, Chevrolet jumped straight to the MkIV designation for its next generation of production big-blocks in 1965. There was a MkII, but it was a race-only, 427ci ‘mystery motor’ from 1963, and the MkIII design never made it to production.