The 1955 Chevrolet design story – Part 1

In this first part of a three-part series on the innovative 1955 Chevrolet, David Temple looks at the development of the small-block V-8 engine that was engineered for the all-new ’55 Chevrolet — and went on to power more than 100 million Chevrolets in total.

Chevrolet took the number-one sales position from Ford in 1927, and for the majority of the succeeding years, Chevy stayed at number one via continuous innovation and keeping up with market trends (and even establishing market trends). However, Ford presented a threat to Chevrolet’s sales supremacy in the early ’50s. From 1949 to 1954, Chevrolet built approximately 7.5 million cars with Ford trailing by as much as 40 percent in calendar-year production through 1951, at which point the sales gap narrowed to about 25 percent. By 1954, Chevrolet’s advantage over Ford was gone. Ford actually bested Chevrolet in model-year production by a little more than 15,000 cars for 1954.

Ford beat Chevrolet to the marketplace with an overhead-valve (OHV) V-8 — the Y-block OHV engine — that was new for Ford’s 1954 model year. Even Studebaker was offering a V-8! Within General Motors, only Chevrolet and Pontiac lacked a V-8. Demand for a V-8 engine was 26 percent of the new-car market in 1950, but quickly grew to 33 percent in 1952 and to 50 percent by 1954, proving that the V-8 was a paramount consideration among buyers of new cars.

By the time the 1952 models were in showrooms, Thomas Keating, Chevrolet’s general manager at the time, warned GM’s Engineering Policy Committee that Chevrolet was “too six-cylinder minded.” His arguments were evidently convincing, because in December 1951, the committee agreed a modern V-8 was needed. General Motors purchased new plants, including facilities in Flint, Mich., for production of the new V-8, as part of a major expansion program the press labeled as, “GM’s Billion Dollar Gamble.”

Passing the V-8 torch

The small-block program started under Edward Kelley, the chief developer of Chevrolet’s “Stovebolt Six” introduced for the 1929 model year (a second-generation version arrived for 1937). Kelley was a respected engineer, but those around him thought he was stuck in the past. The first attempt at a new V-8 was a scaled-down version of Cadillac’s 331, released for 1949. Kelley’s V-8 displaced 231 cubic inches and was essentially complete when engineer Edward N. Cole was assigned to take over the project in May 1952. (Kelley was moved over to head the manufacturing side of the upcoming V-8.) Cole understood the Cadillac-based engine had little potential for growth, was relatively heavy and had unacceptably high production costs for Chevrolet. Furthermore, he believed new manufacturing methods were necessary to significantly reduce the cost of mass-producing Chevy’s forthcoming V-8. Cost was as critical a factor as any engineering specification!

In the book, “Chevrolet 1955 – Creating the Original” by Michael Lamm, Ed Cole is quoted as saying in regard to the engine developed under Kelley, “… you lay down a design and you start making just little changes on an existing design without starting with a clean sheet of paper. What we did was to start with a clean-sheet approach. We did that with the entire car.” His “clean sheet approach” included a different way to cast the engine block: “I felt there were other ways to make that engine; make it better, more precise and less costly… we decided to make the precision cylinder block, which became the heart of the engine… We used the green-sand core for the valley between the bores — the 90 degree V-angle in the center. We used a green-sand core to eliminate [most of] the dry-sand cores [used previously]. Getting rid of the dry-sand cores let us cast the block upside down. That allowed the plate that held the bore cores to be accurately located, so the wall thickness could be controlled. And we could cast down to 5/32-inch jacket walls.” The green-sand technique, according to Cole, “was a combination of ideas,” and he credited John Dolza, of the GM Engineering Staff, as having “as much to do with that as anybody.” The new block-casting technique delivered much higher precision cylinder bores and represented a breakthrough in thin-wall castings.

Initially, the new engine’s displacement was specified as 245 cubic inches, but was soon increased to a range of 260 to 265 cubic inches, and ultimately, the latter was chosen. This change was judged as necessary to keep pace with the trend of ever-increasing displacements. Bore centers were firmly established at 4.4 inches which, in turn, determined the length of the crankshaft and other parameters leading to a compact cylinder block that was 21.75 inches long.

The resulting “Turbo-Fire V-8,” as it was labeled, was a compact over-square (larger bore size than stroke) design featuring hollow pushrods, independent stamped-metal rocker arms, an intake manifold which also served as the valley pan, interchangeable heads, a superior heat rejection rate compared to the straight-six, fully water-jacketed ports, aluminum pistons, a relatively high compression ratio, wedge-shaped combustion chamber and a pressed forged steel crankshaft rather than alloy iron.

According to the “1955 Chevrolet Engineering Features” manual, the 265 V-8 had one of the best stroke-to-bore ratios (0.8:1) attained up to that time in an over-square design, noting that it offered less piston travel per mile of vehicle travel, lower reciprocating loads for smooth operation, and materially less wear on the pistons, rings and cylinder bores. Its 8.0:1 compression ratio (a higher ratio than in the past) improved fuel economy and power. (The availability of increasingly higher octane fuel made possible higher compression ratios. At the time, engineers could foresee going as high as 12:1 for production engines.) The compact size (cylinder block length less than 22 inches) resulted in high structural rigidity and allowed ample installation clearance within the engine compartment for easy serviceability.

The engine’s wedge-shaped combustion chamber had, as explained in the 1955 Chevrolet Engineering Features manual, “a large quench area for control of detonation. This flat quench area also acts as a squish surface when the intake mixture is compressed by the piston. As the piston rises, the mixture is forced away from the squish area, imparting turbulence to the fuel-air mixture and assuring fast and complete combustion. The cylinder head design places the spark plug in the hottest area of the combustion pocket. When ignition occurs, the flame spreads evenly and rapidly throughout the combustion chamber for a smooth pressure rise and freedom from detonation. A portion of the cylinder head forms a lip which overhangs the cylinder bore and protects the spark plugs from oil which may be scrapped off the cylinder walls by the piston rings, thus ensuring reliable ignition.”

As compression ratios increased during this era, consideration had to be given to preventing detonation, or premature combustion of the fuel-air mixture, which can impart destructive forces upon the pistons. Higher compression was a key component to increasing power as well as economy from engines, and was made possible by tetraethyl lead, a fuel additive. The heads, by the way, were interchangeable, which eliminated the need to produce left and right versions, thus lowering production costs.

Inside Chevy’s first small-block

Hollow pushrods allowed for splash lubrication to the rockers and valve stems, thus eliminating the need for separate oil lines, as well as the typical oil passages in the heads. The idea was not new, though; hollow pushrods had been in use for about a half century by this point. Still, there were other issues regarding the rocker arm mechanism, which required innovation. In “Chevrolet 1955: Creating the Original,” Harry Barr was quoted: “There were problems with the hemispherical ball; the mating surface of the rocker arms. Also in the amount of the oil that came up through the hydraulic lifters. One of our engineers, [Bob] Papenguth was his name… came up with a little wafer, a method of metering that oil in the lifter… a little logjam that was essentially overcome. Then there was the mating surface between the rocker ball and the arm to be sure that contact was broken. That contact was heavier at the lower surface. In other words, [we needed] some mismatch of contact [in order for the oil to get between the two surfaces]. And then [we had to have] the right amount of [oil] metering and distribution.” That matter was still not exactly right when the engine went into production. Early engines had squeaks at the rocker balls and there were other problems which had to be fixed. Three holes were drilled horizontally into the block — one main and two tappet oil galleries. A drilled hole from the high-pressure main oil gallery aligned with a hole in the camshaft rear bearing shell to maintain steady oil flow under high pressure to it and through another hole to each of the tappet galleries.

The stamped sheet metal rocker arm originated at Pontiac and is credited to an engineer named Clayton Leach while working on the division’s V-8 in 1947. (Pontiac’s V-8 program experienced a number of delays before finally arriving for 1955.) Chevrolet’s engineers consulted with the manufacturing group that soon determined the stamped rocker arm could be made without the need for any machining. It was an important development during the process of engineering the small-block, because it allowed for the assembly of a lightweight valve train, which gave the small block the ability to safely rev up to about 5,500 to 6,000 rpm. According to Leach, who was interviewed by Lamm, “So Chevy, in order to prevent too much oil from flying around, going down the exhaust valves into the combustion chamber… Chevrolet decided to save some money by not drilling the passages to the main ball pivots which carry, of course, the main load. And when they did that, they had to get some lubrication on that, so they had to drill a small hole in the pushrod socket in the rocker arm…” Incidentally, the rocker arm covers were designed with aesthetics in mind. Ed Cole believed they should have as nice an appearance to them as cost considerations would allow, hence the stylish Chevrolet script across the top.

Turbo-Fire’s fully water-jacketed ports and aluminum pistons provided an improved heat dissipation rate. (The superior heat dissipation allowed for a lighter radiator which, in turn, further reduced production costs.) The “autothermic” slipper-type piston with three rings had a circumferential expander for the single oil ring which provided axial and radial force to control the burning of oil. Piston pins were pressed in place, which eliminated the need to slit the rod and a locking bolt. The short stroke naturally kept the rod length relatively short. This, in combination with the use of aluminum pistons, reduced the overall reciprocating mass.

New forging techniques made possible a rather short crankshaft and reduced torsional vibration. Testing showed the vibration levels to have very low peaks without sharp peaks throughout much of the rpm range; a harmonic balancer canceled the remaining vibration. New technological and processing developments had to be adopted to balance the engine. Its crankshaft was partially balanced on a new machine with electronically controlled indicators; final balancing of the assembled engine was accomplished on another new device that could stop the rotation at an out-of-balance point and drill the front and rear crankshaft counterweights the required amount to achieve balance.

Also important in regard to damping engine vibration was the dynamically balanced four-point “Poised-Power” engine mount setup for the V-8 (as well as the six-cylinder). The four mounting points were inclined so that the roll axis derived resulted in only minor reactions to the frame and body from the engine torque produced. In front were two strut-type mounts, each consisting of four circular rubber biscuits on a metal spacing stud secured to a bracket on the front lower corner of the cylinder block and perpendicular to a seat on the frame front cross member. A set of the rubber biscuits was placed on either side of the bracket and likewise on either side of the cross member. Two shear-type mounts were in back. They attached to the lower rear edges of the clutch housing, and the engine mounting brackets welded to the frame side members. The mounts consisted of two brackets separated by bonded rubber. The rubber acted in shear upon engine roll and in both shear and compression for engine support.

Off and running

Fifteen weeks after taking charge of the program, Ed Cole had the first prototype Chevy V-8 ready for testing. Less than two years after the first prototype engine was built, the new small-block was in production. In all, about 2,900 people were responsible for the engineering of the 1955 Chevrolet. One of them included Assistant Chief Engineer Harry Barr, with whom Cole worked when designing the Cadillac OHV V-8.

The 265-cid Turbo-Fire was offered in two versions for most of the 1955 model year. Both came bolted to one of three transmissions offered – the standard three-speed transmission, the optional three-speed with overdrive or the optional Powerglide automatic. The base 265 had a Rochester two-barrel carburetor and was rated at 162 hp at 4,400 rpm and had a torque rating of 257 lb.-ft. at 2,200 rpm. It added $ 99 to the base price of any model. The 265-cid V-8 with the “Power-Pack” Carter four-barrel carburetor became available shortly after the start of the 1955 model year and was rated at 180 hp at 4,600 rpm while torque was advertised as 260 lb.-ft. at 2,800 rpm. A special air cleaner and a dual exhaust system (except in station wagons, which had a fuel tank shape preventing the use of a second exhaust pipe) was included with the Power Pack. To get the Power Pack option, the buyer had to pay an additional $ 59.20 above the $ 99 base price of the V-8, thus it cost $ 158.20. (A 154 hp version with 7.5:1 compression was an option for Second Series 1955 Chevrolet pickup trucks.) Very late in the model year, a Super Turbo-Fire version packing 195 hp became available.

Compared to the six-cylinder 1953-’54 Chevrolets, the V-8 1955s offered great improvement in performance. A 1954 Bel Air with Powerglide required about 18.1 seconds from a stop to reach 60 mph. A 1955 Chevrolet powered by the 180-hp engine, however, cut that time by almost half, according to a road test conducted by Motor Trend.

Though the new engine plant in Flint operated at maximum capacity, it was not enough; additional V-8 production had to be performed at the Tonawanda (New York) plant. Despite this, demand still outpaced production capacity and some sales were lost because of buyers who chose not to wait for a V-8 Chevy. Forty-three percent of the people purchasing a 1955 Chevrolet opted for the 265.

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