The W43: Oldsmobile's DOHC 455 V8 That Never Was - Street Muscle (2024)

When you think of performance cars, Oldsmobile is not the first thing that pops into your mind. But there was a time in the late-1960s when noted automotive journalist Karl Ludvigsen made the now-preposterous claim that the W43 Olds 455 was “perhaps the most promising and impressive big-bore V-8 engines ever groomed for street and track use by any manufacturer.”

So if you’re thinking, “What’s the deal with this W-43, and how come I’ve never heard of its awesomeness?” read on.


The W43: Oldsmobile's DOHC 455 V8 That Never Was - Street Muscle (2)

The original Rocket V8. Image: GM Photo Store

Find a sun-baked Old Skool hot rodder from the West Coast and he may give you an earful on the wonders of the Rocket V8. Along with Cadillac, Oldsmobile was the first to debut a high compression V8, which the burgeoning hot rod set heartily embraced. Why were they burgeoning?

Because when our servicemen came back from overseas after defeating Nazi slime, they were a restless, wild bunch who had a tremendous amount of technical know-how and were aching to use it. The “Flathead” Ford V8 (especially with a Mercury crankshaft) became the hot setup during that time, and engineers began creating and selling aftermarket parts to hop them up.

These motors appeared in just about anything one could get his hands on, although they often were installed in cheap, plentiful Fords from the 1920-30s.

And then Olds introduced the Rocket V8 in 1949. Offering up to 135 horsepower from 303 cubic inches, it put a stock Flathead to shame. It also was the first Olds to inspire a song since “My Merry Oldsmobile” in 1905 – Ike Turner and Jackie Brenston wrote an ode to the Rocket 88, Oldsmobile’s cheapest and lightest car equipped with the Rocket V8.

If you wanted to go fast in the early 1950s, it wasn’t unusual to go the Oldsmobile route and come out on top. Not until Chrysler’s HEMI in 1951 did Oldsmobile begin to feel the pressure and then, in 1955, with the small-block Chevy, it was all over.

Nineteen sixty-six saw the mid-year introduction of the W30 Force-Air package, which was the first of many “W” performance designations (F-85/Cutlass W31, Toronado W34, W25 fiberglass ram air hood, and W27 aluminum axle carrier and cover, among others).

So when Oldsmobile engineers began development of a super-high performance V8, it was only logical that it too would receive the W treatment, in this case W43. Development began in 1968 for a 1972 debut, but GM’s decision to lower compression for all its motors for the 1971 model year due to emissions concerns ensured that the W43 would not see fruition.

The W43 455 in all its glory - note the three breathers. Image: Hi-Performance Cars magazine

Think back to 1967 for a moment – the muscle car market was cresting in popularity. Pontiac had just sold almost 100,000 GTOs. Chrysler was finally fielding cars with proper muscular identities (Plymouth GTX and Coronet R/T). GM released its F-bodies to compete with the Mustang. And, over at Lansing, Oldsmobile engineers were busy trying to figure out how to make the 4-4-2 with the W30 package even faster.

GM had a new edict banning multiple carburetion on anything other than the Corvette, so the 4-4-2 had to make do with the new Quadrajet. The engineers were not satisfied, so they created a new performance objective that led to the approval of the W43: A four valve per cylinder, semi-hemi pushrod V8 based on the new-for-1968 Rocket 455.

Oldsmobile engineers kept available components whenever possible to make the project feasible. The block was basically stock although the W43 was engineered to be either an iron or aluminum block and heads.

Minor modifications were made for better oil supply for the valve gear, the bottom end was beefed up, and four-bolt caps were added to the main bearing journals.

Cylinder heads were developed using mahogany bucks. The ports were tested for air flow; according to the May, 1971 issue of Hot Rod, engineers placed a partial vacuum on the combustion chamber side of the buck and then measured the volume of air drawn through the port with the valves open at different degrees.

Heads show semi-hemi combustion chamber with central spark. Image: Hi-Performance Cars magazine

With initial testing, engineers discovered that the cam lobes and pushrods were not holding up. One of the causes was due to the high angularity between the pushrods and the lifters. To rectify this, the engineers had new blocks cast with raised camshafts, which required removable lifter galleries not only to keep the lifters in place, but also so they could be installed as well as the bores machined. Pushrods were increased from 5/16 to 3/8-inch. In this configuration, the W-43 was putting out 440 horsepower at 4600 rpm with the standard W-30 cam and Webers.

Then the engineers took things even further…

This ain't your father's Oldsmobile - OW43 with Webers! Image: Special-Interest Autos magazine

Four months later, and inspired by racing (on both water and land), Oldsmobile engineers decided to add dual overhead cams. A gear drive supported by roller bearings in an aluminum gear case handled the cam chores, while a dummy camshaft was used in the standard position for the oil pump and distributor.The cams were also drilled to carry oil in their journals.

Interestingly, the cams were on the cylinder head, and the gear drive on the nose of the crankshaft was in the block, creating a variation in the heights of numerous components. On paper it sounded like trouble, but it worked without a hitch.

Dyno testing the 12.2:1 OW43 at the end of 1969 showed the DOHC motor having a very level torque curve. Peak power Olds engineers recorded was 700 horsepower at close to 7000 rpm at the crank. This was achieved with no cam profile development to match the four-valve layout.

But, on January 1970, General Motors President Edward N. Cole put the kibosh on the project and more as he announced that all GM divisions would lower the compression of their motors so 91 octane unleaded fuel could be used.

DOHC gears were supported by ball bearings. Image: Hot Rod magazine

Below is a list of parts of components and descriptions by engine series.

Earlier in the decade, Oldsmobile engineers had created a mahogany airflow testing rig to evaluate port and valve combinations. As the trials progressed, engineers would make modifications with clay. They also devised a method to measure the amount of air that passes through both intake and exhaust valves.

New-for-1968 455 cid block with 4.125-inch bores and 4.250-inch stroke.

Reynolds 356 alloy.

3.00-inch main bearings with 4-bolt main bearing caps and 2.50-inch rod journals

An interesting thing happened with the cast iron camshaft as development progressed: Engineers designed new cam bearing journals and revised the front sprocket cover to raise the cam 1.035 inches. This was done to solve the problem of excessive wear on the rockers based on the angle of the pushrods.

Small cracks developed around the cam drive housing, so new cams were designed to achieve full balance of each pair of lobes. They also were drilled to carry oil to the bearings.

Five identical idlers were used – four for the camshafts and one functioning as a gear for the dummy camshaft in the middle of the block. Each gear, which was supported by ball bearings, was ½-inch wide, 5.2 inches in diameter, and had 52 teeth. Additionally, a ring of nine irregularly spaced holes allowed the timing to be adjusted based on the positioning of the camshaft and drive gear. This allowed timing to vary no more than 0.6250 degrees from the ideal.

Two other versions with different camshaft drives were developed before the W43/OW43 program was cancelled. The OMW43 used a chain drive designed by Morse, instead of gears. It had a separate single-roller chain for each bank. The OLW43 used a Link-Belt chain drive system.

Most testing was done with a ratio of 10.2:1 on 104 octane fuel.

Forgedtrue developed 12.2:1 pistons for the DOHC.

Stock SAE 1140 forged steel.

Machined Carrillo rods.

Symmetrical design in iron or aluminum. Latter versions saved 75 lbs. from stock 455 motor. Inlet ports were pinched due to the pushrod passing through. Semi-hemi design had spark plug in the middle of the four valves.

Aluminum heads weighted 50 lbs. from stock 455 motor even with DOHC due to compactness of 4-valve configuration. Inlet ports were not pinched.

What made the W43 stand out from other experimental engines was its 4-valve configuration. Image: Car Craft magazine


Made of aluminum and designed to take either a Rochester or NASCAR Holley four-barrel carburetor. Another one was developed to take either Weber carburetors or Lucas fuel injection.

Stock but with addition of 5/8-inch drain holes for oil drainback.

Dry sump oil system with pressure pump in-between two scavenge pumps.

Both forged and cast pistons were used, although most testing was done with forged.

Forgedtrue developed 12.2:1 pistons.


Even back then, using pushrods for four-valve heads was unusual. Oldsmobile engineers devised a system of two rocker shafts with four forked rocker arms on each shaft. The rocker shafts are carried along each cylinder head by five cast pylons. Size increased from 5/16- to 3/8-inches.

The DOHC OW43 with Webers. Image: Hot Rod magazine

Initially cast iron, it was discovered that there was an extreme amount of friction between the rocker and the shaft, which was caused partly due to the placement of the pushrod arm at the end of the pushrod body.

Adopting a forged aluminum rocker arm running on twin inserted needle bearings helped partially solve the problem. The other solution was to reduce the angle of the pushrods.

The chamber required no more than 29-30 degrees of spark advance. In comparison, the stock motor would have required 37-38 degrees.

Post-1966 Buicks are known to use spark plugs that had a conical seat rather than compressed washer seal. This allowed closer water jacketing around the plug. Olds engineers used a similar 14mm design but with a smaller 5/8-inch hex. With the semi-hemi design, plugs were placed smack dab in the middle of the head.

The initial head was aluminum with a layout calling for 1.750-in intake valves made of SAE 8640 steel and inclined at 22 degrees, and 1.375-in exhaust valves made of 214N austenitic stainless steel, and inclined at 15 degrees. Valve guides of both bronze and iron were used, although iron was used for most of the testing.

Olds engineers discovered that when the two intake valves were fully open, there wasn’t an advantage to the conventional two-valve head. However, they realized that when the two intake valves were partially open, they were able to pass much more air and fuel than the conventional head.

Engineers also tested a three-valve design with two intake/one exhaust configuration, but the spark plug placement and coolant flow was less than desirable.

Valve clearance adjustment system was handled in a unique manner. Inside each tappet, between it and the valve stem, was a hardened steel disc to assist in the distribution of force when the valve was actuated. Clearance was set by a steel shim that was inserted between the disc and the tappet.

Springs were the same diameter as those used on the W-30 but were 0.192-inches longer to allow experimentation with higher lift. Engineers tried combinations with inner/outer dampers and springs.

One of the few surviving examples of the W43. Image:

The W43: Oldsmobile's DOHC 455 V8 That Never Was - Street Muscle (2024)
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