Chevrolet’s W-Series V-8 Details
The Chevrolet W-Series V-8
Horsepower Ruled in 1960
If you were young back in the early 60s, the lure of fast cars and high horsepower likely caught you. After all, back then, America was all about flashy cars with powerful engines as an entry into adulthood. Chevrolet knew this to be true, having sold a heck of a lot of high horsepowerV-8s in the years 1955-1960. Chevrolet also new that there was a “horsepower war” out there – GM brother Pontiac, Ford, and every single Chrysler product were preaching more, more more each and every day.
As a kid, you poured over each and every magazine and newspaper article you could find to see who was offering what hot engine option and just how hot it was. By 1961 it was apparent that the Chrysler B and RB blocks were making some serious grunt with 383 and 413 cubic inches and multiple carburetion and Pontiac had announced the release of their 421 CID block in response. Mercury had released their M-400 430 CID block in ’58 so everyone knew Ford could be there if they wanted.
Chevy had thought they had the bases covered with their “W-Series” big block that had been introduced in 1958 at 348 CID. They’d increased the horsepower of this block up to 350 ponies, and they thought that was enough. But an adage of the time that circulated was “There’s no substitute for cubic inches”, (Sports Cars Illustrated February 1957). and suddenly their competition was moving way ahead of them. And they knew Ford would be announcing their new 390 CID V-8 for 1961 . . . . Chevrolet was ready to act.
A 409 cubic inch version of the “W” engine was released in 1961 on December 17, 1960 for 1961 Chevrolets. They did this in conjunction with the Impala SS (Super Sport) model offering. The Impala SS could only be had with the 409 early on. Chevrolet intended to make “SS” synonymous with “409”. This would later change.= and SS would denote the sportiest Impala.
To make the 409, the bore and stroke were upped to 4.312″ x 3.50″, but the engine was still very much over square. While the 348 had been seen as a great competitor, the 409 would solidify Chevrolet as the one to beat in drag racing. You can see a 1961 comparison of the 348 and the 409 in the 1961 Drag test of the 409 from Motor Life magazine that is discussed in this magazine and can also be downloaded as a PDF HERE. Chevrolet easily outdistanced the Ford 391 and forced Ford to 406 CID in the 1962 model year – a key marketing target for the GM division. In fact, the 409 forced Plymouth and Dodge to use their new mid-size body in 1962, and had Pontiac planning their lightweights for 1963. Chevrolet would respond with their Z11 package (see below).
Learning About the W-Series V-8
The big block V8 Chevrolet engine was called the “W” series. It was released in 1958 for passenger car and truck use. The engine had offset valves (see illustration) which resulted in the unique scalloped rocker covers, giving it a very distinctive appearance. The offset valves were not designed with any mechanical advantage in mind – it was done to reduce the block’s overall length as Chevrolet wanted to be sure it could fit in the shorter GM B-Body extant in 1955-57 when the engine was designed. This became moot as the GM cars grew in wheelbase, but it did result in a rather compact engine for its cubic inch displacement. This offset valve design did, however, allow the fitment of larger valves without any major redesign or machining.
The “W” series was produced from 1958 to 1965, with three displacements offered: 348 CID, offered from 1958-1961 in cars, and through 1964 in trucks; 409 CID, offered from 1961-1965; and 427 CID, available only in 1963 in a special Z11 drag racing package. The “W” big block had a dry weight of approximately 665 pounds, depending on intake manifold and carburetion. It was a physically massive engine when compared to the Chevrolet small block.
The block had 4.84″ bore centers, two-bolt main bearing caps, a lubrication system with the main oil gallery located low on the driver’s side of the crankcase similar to Ford’s “side oiler” system and quite unique for its day. The heads used on the high performance 409 and 427 engines had larger ports and valves than those used on the 348 and the base 409 passenger car and truck engines, but were externally identical to the standard units and must be identified by casting number.
A minor difference between the 348 and 409-427 engines was the location of the engine oil dipstick: it was on the driver side on the 348 and passenger side on 409-427. As with the 265 and 283 cubic inch small block engines, the “W” engine valve gear consists of tubular steel push rods operating stud-mounted, stamped steel rocker arms. The push rods also act as a conduit for oil flow to the valve gear. These stamped steel rockers allowed for the offsetting of the valves, as no rocker shaft was necessary. An added benefit of the rockers was that due to the relatively low mass of the valve train, the “W” engine were capable of operating at RPMs beyond 6000 RPM, however, the unique head design and combustion chamber limited HP above 5,800 rpm.
And unlike many of its contemporaries, the “W” combustion chamber was in the upper part of the cylinder bore, not in the head, with the head having only tiny recesses for the valves. This arrangement was achieved by machining the block at milled at a 74 degree angle rather than 90, creating a raised portion of the block toward the outward side which in the bore, became the combustion chamber. The concept for this unique head was to maximize brake mean effective pressure (BMEP) at relatively low engine speeds, resulting in a very fat torque curve. It was essentially the same basic idea as used by Ford’s 383-430 CID MEL engine, which also appeared in 1958. Both of these designs were known more for their torque than their top end.
A crowned piston was used to designate the combustion chamber, a concept in American production engines shared only with the aforementioned Ford MEL block. As the piston approached top dead center, the angle of the crown combined with that of the head deck to form a wedge shaped combustion chamber with a pronounced quench area. The spark plug protruded vertically into this chamber, which tended to cause a rapidly moving flame front during combustion.
Eventually, this design would be considered difficult for production and especially service, in that truing up the head by milling, required re-sinking the valves and trimming the tops of the valve stems. But he major issue was that the horsepower fell off at high RPM in racing applications.
With various tweaks and some serious addition of cubes, the “W” held its own on the street and drag strip. Where it did not fare as well was in NASCAR, where the configuration did not lend itself to sustained high rpm. Thus, development began on a second generation big-block in final iteration, that when released in 1965, would be called the “Mark IV”, known more familiarly as the “Rat”.
The first “W” engine was the 1958 “Turbo-Thrust” 348-cubic-inch V8, thought to be originally designed and intended for use in Chevrolet trucks, but this was not completely true. Engineers realized that the 265-283 “small block” could not produce enough torque to add effective performance at moderate RPMs in the larger, heavier 1958 passenger car line that was projected. It was also a response to the climbing engine sizes of the competition. The bore was 4.125″ and stroke was 3.25″, a substantially over-square design.
With a four-barrel carburetor, the base Turbo-Thrust produced 250 HP. A special “Tri-Power” triple-two-barrel version, called the “Super Turbo-Thrust” produced 280 HP, and a “Special Turbo-Thrust” upped the output to 305, utilizing a single large four-barrel. The higher horsepower engines were equipped with dual point distributors, improved head’s and 2 1/2″exhaust.
Mechanical lifters and the three two-barrel carburetors brought the “Special Super Turbo-Thrust” up to 315 HP. In 1959 and 1960, high-output versions of the top two engines were produced with 320 HP and 335 HP respectively. In 1961, power was again increased to 340 HP for the single four-barrel model, and 350 HP when equipped with three two-barrels.
The 409 became Chevrolet’s top-of-the-line regular production engine from 1962 through 1965, with a choice of single or dual-four-barrel carburetion. The initial version of the 409 engine produced 360 HP, with a single-four-barrel Carter AFB carburetor.
The same engine was upped to 380 HP in 1962. A 409 HP version of this engine was also available, with a dual-four-barrel aluminum intake manifold and two Carter AFB carburetors.
In the 1963 model year, the 409’s output reached 425 HP at 6200 rpm with the same 2 4-barrel manifold, 11.25:1 compression and a new solid lifter camshaft. In addition, a 340 HP version of the 409 engine was available from 1963-1965, with a single-four-barrel cast-iron intake mounting a Rochester 4GC carburetor, and a hydraulic-lifter camshaft.
The 400 HP engine was available through January 1965, while the 425 HP engine was retired at the end of the 1964 model year. The 409 high output V-8 was replaced by the 396-CID 425 HP Mark IV big-block engine. and the 340 HP 409 was replaced by the 325 HP 396 CID V-8.
427 CID Z11
A special 427 cubic inch version of the 409 engine was available for the 1963 Chevrolet Impala Sport Coupe when ordered under Chevrolet Regular Production Option (RPO) Z11. This was a special package created for drag racers, including some aluminum engine and body parts and a cowl-induction air intake system, a a package along with this new 427 “W” engine. Unlike the later second generation Mark IV 427, it was still based on the W-Series 409 engine, but with a longer 3.65″ stroke.
A high-rise two piece aluminum intake manifold and dual Carter AFB carbs fed a 13.5:1 compression ratio which produces a very under-rated 430 HP and 435 ft. lbs of torque. Fifty RPO Z11 cars were eventually produced. GM Documents show 50 Z11 engines were built at the GM Tonawanda engine plant, and that 20 partial engines were made for replacement/over the counter sale. (See more Z-11 info HERE).