The Hudson Wide Block I-6

NOTE: When describing various engines, the term “L-Head” is often used. L-Head engines have their valves in the block, not in the head.

The L-Head or “Flat Head” or “Valve in Block” design is an early but proven engine design. It is less complex and easier to manufacture, but suffers from poor intake and exhaust flow when compared to OHV designs.

Hudson Wide Block: 232, 262 and 308 CID.

In 1951 Hudson released the “Wide Block” Big Six. In addition to the 232 and 262 CID, a new size engine, the 308 CID “Hornet” specific engine was added. Two key parts of the upgrades were that the cylinder head water passages were improved and the block has a lower end (crankcase) kick-out to accommodate the longer stroke crankshaft of the 308 CID version.

A Wide Block 308 CID engine block showing the crankcase “kick out” to accommodate to longer stroke arc of the 308 CID engine.

All Wide Block Big Six engines received hand-fitted pistons and bearings during production. As such, the size information for each piston was hand-stamped into the block behind the lifter and valve covers on the right-hand side of the block. Hudson’s attention to detail resulted in excellent power for a L-Head engine, as the engines were assembled with the utmost care (almost blueprinted) when assembled at the factory.

The crankshaft flywheel flange uses 7/16″ bolts pressed into the crank, and with a special lock plate for the nuts. These smaller size bolts have been an issue since the beginning of production, sometimes resulting in the bolts shearing from the engine’s torque. Flywheels for both stick and Hydra-Matic transmission cars must be sealed to the crankshaft to prevent leaks, using good high quality sealer.

All Wide Block engines are suitable for stock through high performance usage. Cylinder heads and oil pans from the Narrow Block do not interchange with the 1951 and later Wide Block Big Six engines.

On the Wide block, the 232 and 262 CID versions retained their same bore and stroke and crankshafts, but the bore of the 308 was increased to 3.8125″ and the stroke was lengthened to 4.500″. The 308 CID version also has stiffening ribs cast into the lower area of the block about 2″ above the oil pan rail.

A Wide Block 308 CID engine block showing the strengthening ribs found only on the 308.

Minor refinements were incorporated in each year of production from 1952 through 1955. As an L-Head engine, the ports are in the block and not in the head, so the block’s valve relief area (the ports, per se) was improved each year to increase air flow over the cylinders. Due to the L-Head’s breathing restrictions, valve sizes for the 232, 262, and 308 CID I-6s were 1.8125″ for the intake and 1.5625″ for the exhaust. These were the valve size through the entire production run from 1951 until 1956. The 308’s valve sizes were increased to a larger 2.00″ intake and 1.6875″ exhaust valves in the 1953-55 “7X” racing engines engines.

All Hudson big six engines used 7/16″ head bolts, except for the “7X” racing engine built specifically by the Hudson Race Shop. These 7X engines used 1/2″ head bolts for added head gasket retention. (Details on the 7X engine is covered below). All 1951-56 Hudson Wide Block engines were assembled with the same care as earlier versions.

In the 1952 model year, in an effort to enhance HP for racing and to be competitive with the then current OHV V-8s on the street, Hudson released dual carburetion, called “Twin H-Power.” The system consisted of a special cast iron intake, two large Carter 1-barrel carburetors with attendant special actuation linkage, their own individual air cleaners, and a special exhaust manifold with two carburetor choke stove pipes in the center two exhaust ports. An example of the Twin H-Power intake is shown in the image above.

Twin-H Power was available for the Wasp 262 CID and the Hornet 308 CID engines. It was not available for the 232 version. Hudson indicated that the dual carbs added 10 horsepower to both 262 and 308 engines. Twin-H was both a factory installed (assembly line) option as well as being available as a dealer over-the-counter add-on kit.


Cylinder Heads.

An aluminum cylinder head was optional on all three engine displacements during this time. In most cases, the aluminum head upped the compression ratio by 0.5 and did give a slight increase in horsepower. Head gasket retention with the aluminum cylinder head was, and is, an issue due to warping and differing expansion rates of the head and block. (If buying a used aluminum cylinder head be sure to ensure it can be machined back to straight and true).

A 308 CID engine block showing the typical L-Head valve relief area that acts as the intake and exhaust port.

Camshaft duration changed several times over the years. The standard factory cam for Hudson 232, 262 and 308 engines is Part # 306344. The lift is 0.356″.

The performance camshafts Hudson used in most engines were the “742” and the “040” cams. Both of these camshafts started out as 7X racing camshafts but are suitable for a daily driven Hudsons. The “742” camshaft had the ramp opening and closing rates altered in 1955-56 for use with hydraulic lifters, and yet work very well with mechanical lifter engines for street performance.

The actual specifications for these two camshafts have never been accurately listed except for the lift. The “742” has .354″ valve lift and the “040” has .390″ valve lift and 268 degrees of duration. Both lift specs are at zero lash. New reground camshafts that offer better performance than these two cams are still available.

1955 & 1956 – Improvements in the AMC years

Some major modifications were made to the 308 CID engine in 1955 at AMC, and it was the only displacement left. The 232 and 262 were dropped and replaced with AMC sixes.  The changes listed below were not driven by the merger, but were improvements that Hudson had already been prepared to make for better durability.

Cylinder head bolt holes were enlarged to the 1/2″ used by the 7X engine for better gasket retention. Cylinder heads for 1955 were now only the 308 version in cast iron or aluminum. In 1956 a low and high-compression head was offered, the low compression head was the 308 cast iron, but for higher compression the 1954 262 CID cast iron head was used. The 308 aluminum hi-comp head was discarded.

A 308 CID engine cylinder head. Red arrow shows the additional area that acts as part of the intake port. Green arrow points to the spark plug hole. Blue arrow shows typical L-Head exhaust porting.

The valve relieve area of the block was enlarged once again for better air flow. The 1955-56 blocks have the best out-of-the-factory unmodified air flow of all Hudson big six engines short of the 7X racing engine.

The lifters were changed at the end of the 1955 model year to hydraulic and a re-profiled “742” camshaft was installed. Most of this change was due to the difficulty in adjusting the valves in the Nash chassis. A special slip-on fuel pump eccentric was added to the arm (1/2 moon shaped) to reduce camshaft fuel pump wear.

Twin-H Power was still available for these two years. In 1955 the intake was changed to incorporate a balance chamber and to assist the adjustment of mechanical lifters, now that the engine was installed in a Nash chassis. These intakes do not flow as well as the 1954 and earlier versions.

The exhaust manifold flange on the Twin-H intake was also changed, so earlier intakes will not fit the 1955-1956 exhaust manifold. The newer exhaust manifold uses a different elbow flange, so the twin outlet elbow (for dual exhaust) will not fit these manifolds.

The crankshaft flywheel flange is 1/2″ shorter than the 1954 and earlier engines and incorporated 1/2″ threaded holes for bolts rather than the 7/16′ bolt-nut combo of previous years. This crankshaft is a much stronger crankshaft, and flywheel retention is no longer a problem as with the earlier style. A modern neoprene seal is used at the rear main location in place of the older rope seals.

Oil pans were changed to a center sump to clear the Nash chassis. Thermostat housings were redesigned to take modern style thermostats, and the water bypass is blocked off by the mounting flange.

7X Race Engine

The 7X engine was released during late 1952 for racing and severe usage. It was only available as a 308 CID version. These engines were not factory installed assembly-line pieces but were available either as a dealer installed option or as a crate engine. Each were hand-built, and many times individually modified in-house by Hudson’s Race Shop, based upon racer demand. They were available on a very limited basis.

A 308 CID 7X Race Engine at the Hostetler Hudson Museum. Arrow shows the unique and special outlet for dual exhausts.

These 7X engine started out with hand selected block cores prior to modification for the least core shift and the thickest cylinder walls for durability. Each engine received larger 2.00″ intake and 1.6875″ exhaust valves. The valve ports and bowls were hand ported and opened to match the larger valve sizes. The relief area was hand-machined to remove any flow restrictions over this area of the block into the cylinder. The head bolt threads were enlarged to 1/2″ diameter for better head gasket retention.

All 7X engines used a 232 CID cylinder head for higher compression. The cast iron 232 head yielded 8.7:1, and with the 232 CID aluminum head it was 9.2:1.

The first cam used was called “7X Flat Top” and also known as the “742” cam, was introduced in April of 1953 and is part # 309742. There were lots of customer complaints about this cam. There was trouble setting it up and it apparently ate timing chains. This camshaft quickly progressed to the “Super 7X” in August of 1953. This cam had part # 311040. The lift is 0.390″ and duration 268 degrees. It has a rough idle and the overlap can be noticed in the loping exhaust note. Clifford engineering makes replacements of the #040 and #742 cam.

Each 7X engine received a Twin-H Power intake, carburetors and a special exhaust manifold with a bolt-on twin outlet elbow for dual exhaust in place of the standard single outlet elbow. The exhaust manifold itself is different internally in the intake manifold heat chamber. The 7X version is totally sealed off from the intake so no direct exhaust gas flows into the intake for an improvement in flow for the center two exhaust ports.

Pistons, bearings and crankshafts were hand-selected and fitted for the best clearances and lowest amount of rotational drag. Horsepower ratings were never given as exact numbers due to the hand fitting and modifications but were listed in various publications as 220-240 HP.

1951-1956 Hudson Wide Block Key Specifications

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