Vintage Engines: Chevrolet's "W" Motor

The debate about what constitutes Detroit's first musclecar will rage on forever among enthusiasts of one marque or another, but there's little doubt that the '61 360hp, 409-powered Chevy Impala SS (Super Sport) is right up there as a powerplant/vehicle that made an indelible mark in the annals of drag racing and street racing. Few engines have ever been named in Billboard Magazine's charting of pop hits, but if it ever came down to an asphalt rumble between those that have been thus immortalized, Chevy fans would be betting on that "four-speed, dual-quad, Posi-traction 409" (Beach Boys, 1962) to come out on top in the lights.

The Chevrolet "W" series, named for the shape of the valve covers resultant to their novel valve arrangement, were produced from 1958 to 1965 in cars and trucks. They were very popular during their day and were made in considerable numbers for performance fullsize sedans. Maybe it seems to some that there are already too many Chevy engines in street rods, but we can recommend this series for availability, price, and performance. When put together with today's improved components, they make an excellent choice for a "vintage-engined, traditional street rod." Their distinctive look and easy-to-find accessories give them high marks on the vintage-engine "cool factor" scale.

W Motor History
The '55 introduction of the modern Chevy V-8 was an undeniable milestone in performance engines. They were lighter, smaller, and revved better than any of the Kettering V-8s used in the other GM marques up to that point, and hot rodders and aftermarket manufacturers were lightning-quick in exploring the speed potential of the engine. The popularity of the Chevy V-8 was further assured when 1957 brought out the bigger 283ci engine and, more importantly, new performance options. The 265 had had few options other than a four-barrel and dual exhausts, but the magic Duntov worked on his Corvettes showed up on regular Chevys in 1957, culminating with the rare option of the 1 horsepower-per-cubic-inch, fuel-injected 283 that cleaned up at oval and straight-line racetracks.

If there was any aspect of their new engine the Bow Tie engineers weren't confident about, it was torque-the kind that could be used for their new trucks, and they had been working on another engine design to serve that purpose. When the 348 came out in 1958, it made such an impression on the public that, although W motors did wind up in trucks, many more were sold in passenger cars, where the increase in cubes was as well-received by the masses for highway cruising in stations wagons as it was by the young hot rodders of the day. While the base-level 283 in 1958 offered 185 hp, the base 348 was introduced at 250 hp That was the single-four-barrel workhorse of the line, but there was also a 280hp version sporting Tri-power carburetion, and later that year a 315hp version of the Tri-power engine that had a bigger, solid-lifter cam and 11:1 pistons was introduced.

Given the long-standing penchant for atomic-age nomenclature at General Motors, the 348 was called the "Turbo-Jet V-8" engine, and was most often backed by the new "Turbo-Glide" automatic transmission (Powerglides were also used), while the triple-carb version had to be called the "Super Turbo-Jet V-8." The small-blocks were designated as "Turbo-Fire" and "Super Turbo-Fire" V-8s, but we've never heard anyone other than a car salesman use such terminology. For stick-shift driving, you could only get a three-speed with the 348, until the option of a BorgWarner T10 four-speed became available in 1959. Many a three-speed was yanked out of 348 cars to substitute the T10. At the time, that brought to life the low-end "across the intersection" torque that made these cars popular with street racers. The sound of uncapped sneaker plugs and a solid-lifter 348 Tri-power wide open and bang-shifted through the gears was nothing less than musical!

It must be mentioned that the design of the 348-and later 409- and 427-inch versions-is somewhat unusual. From looking at modern engines, we expect to see a wedge-shaped chamber with the valves side by side. In the W motors, the cylinder head had the valves arranged with the intake valve closer to the intake side of the head and exhaust valve toward the exhaust side, allowing for fairly large ports that didn't neck down as much as typical wedge heads. The other startling difference was the combustion chamber, which was basically in the cylinder, not the head! The head is almost a flat slab with a small open area around each valve head, amounting to about 10 cc. What would be the wedge part of the chamber is in the top of the cylinder and the angled roof of the pistons, because the head-mounting surface of these engines is not perpendicular to the bore, but at a 16-degree angle. Thus, when the piston comes up, it sees a wedge-shaped chamber above it; it just isn't part of the head.

It must have seemed a little unusual to performance machine shops that were used to boring and decking engines where the deck was 90 degrees to the bores. One exception to this design was on the '62-65 truck engines that had a more conventional chamber around the valves, in the head. All of the W motors had a "pent-roof" piston top with a short angle on one side that put that area close to the head plane for good squish on the mixture, while the other sloped side of the piston top delineated the main space of the chamber, along with a "counterbore" about 0.060 inch deep in the side of the block above the piston travel, in a radius around the exhaust side of the cylinder.

Additionally, most W motors also have a deeper "notch" machined in below the exhaust valve area. All 348 passenger-car and '62-65 348 truck engines have this notch, as do '62-65 409 truck engines. All passenger-car 409s have the counterbore, but without a notch. The only blocks to avoid for performance use are the '58-61 348 truck engines, which have two notches to reduce compression. There's almost no way to fit a piston in these blocks that can achieve even a 9:1 compression ratio.

Despite the big Detroit automakers having signed their famous agreement in 1957 to end all support of racing, the over-the-counter sales of racing cars and parts just went underground, and development of trick "factory" parts continued on both the small-blocks and the W motors, which were actually Chevy's big-blocks of the day.

Ford and Chrysler were both vying with GM to dominate the stock classes in drag racing, and each manufacturer kept upping the ante with hotter and bigger engines. The 348 probably has some distinction as having been offered in 10 different factory horsepower ratings over its four-year span! To keep up with the Oldsmobiles, Buicks, Cadillacs, Pontiacs, and the non-GM engines in the fray, Chevrolet needed more cubic inches, and the answer was the legendary 409.

Introduced in 1961, the 409 gained all those extra cubes via the usual suspects-increased bore and stroke. Like the 348s, the 409 engines were also used in Chevrolet trucks, but the company's focus was on gaining youth attention via street, dragstrip, and NASCAR performance. No manufacturer wanted to be left out at the start of this youth-oriented market of the 1960s. The 409 did all that, and having a hit song didn't hurt the legendary status one bit. The Beach Boys had their initial release of "Surfin' Safari" in 1961, but it was released again to wider distribution when they got a real record contract the next year, with "409" on the B side. It became one of those rare 45s that had a very popular song on each side. To any young man who didn't grow up in California, "409" and, later, "Little GTO," "Little Old Lady from Pasadena," and other musclecar songs just further cemented the magic of the Left Coast we imagined was filled with sunshine, great girls and beaches, and where everyone drove a hot rod or musclecar.

Some of the great names in drag racing earned their chops tuning and driving 409-powered Impalas, Bel Airs, Biscaynes, or Del Reys from 1961 to 1963. There's no forgetting "Dyno" Don Nicholson, Dave Strickler, Hayden Proffitt, and many others around the country who cut their teeth chewing up the 401-406 Fords and 413 Mopars. The 409 came onto the Chevrolet option lists in 1961 with 360 hp, 11.25:1 compression, and a single Carter AFB four-barrel. That was good, but just as with the 348, new performance versions were introduced constantly. In 1962, the 360hp version was joined by the magic 409hp model with dual quads. One horsepower per cubic inch is still a good target for modern-performance V-8s, but back then the 283hp/283 and 409hp/409 had great bragging rights with what is today considered old-school technology.

Of course, Chevrolet didn't actually make the racing extras that went to favored racers around the country; they just put the "stock" engine into bodies that happened to be extra-light. One racer tells of receiving his aluminum body panel package for his 409 at his motel, which is where he installed it during the night on his car, along with the camshaft he had been handed. The next day at the major drag meet he was in, he asked the Chevrolet guy if the cam was going to be legal for NHRA B/Stock, and the guy next to him said, "It'll be worth a half-second, and Monday it will be listed at dealerships with a Chevrolet part number." The guy was Bruce Crower, who had just given the racer a pre-production cam. Incorporating aftermarket speed equipment into their parts catalogs kept auto manufacturers in the game.

The next year, the sharply styled '63 Chevys could be ordered with 409 powers of 340, 400, or 425 hp, as Chevrolet engineers kept coming up with higher-winding valvetrains, and these versions continued into 1964. However, a new development in 1963 unwittingly started the W motors toward the exit door.

As the unofficial factory "race" for the winningest engines accelerated, ever-larger engines were introduced. Chevrolet's answer was the famous RPO-Z11 (regular production option) for 1963, which was a 409-based engine stroked to 427 ci, and fitted with high-rise dual-AFB intake, cowl induction, and 13.5:1 compression. Only available on the Impala Sport Coupe, this drag package also included aluminum front-end components, and it was hot! Only 57 were made, of which it is said only seven are still around in one piece. During this heady period, such obviously race-only limited-production cars ran in the Super/Stock class, so everyday guys with 409s could still run in A/Stock, but many Z-11s saw continued service in Modified production classes, and later on in the F/X class that developed into the altered-wheelbase predecessors to Funny Cars. This was all cool, but the engineers were hard at work developing a "second generation" of big-block engine, which was released in 1965 as the new "396 Turbo-Jet," the first of the Rat motors we all love. This was the last year for the W motors, but what a legacy they laid down.