Super Stock Hemi Plymouth

The Dominance of Mopar in the Mid-1960s

Dodge and Plymouth had their teams, and even though beating GM and Ford was the focus of the efforts, these competition Mopars ended up racing other Mopars for honors. The mid-’60s were filled with all sorts of hot Chrysler-powered racecars, and the biggest single reason for this success was simple: the very powerful 426 Hemi racing engine. Anyone who was around racing during this era could tell stories of individual cars from factory and independent teams, as there were plenty of fast Hemis. But the thing about racing is that the next year would always see attention directed to the new wave of production cars; the old racecars soon fell to lower classes and were even forgotten as time marched on.

The Unique Survivors: 1965 Super Stock Hemi Plymouths

However, because the Dodge and Plymouths that were built for Super Stock competition in 1965 were unique in design and performed well, some did survive, and these are highly cherished today by collectors and enthusiasts of quarter-mile drag racing. This ’65 Plymouth Belvedere I with the “Super Commando 426” package is one of 101 originally built and is among one of the best remaining examples of these cars. Thanks to its flawless Roger Gibson restoration (Scott City, Missouri) and attention to detail, the machine is like a rolling time capsule back to the glory days of Super Stock racing.

The Special Attention Given to the 1965 Plymouth Super Stocks

What made this Plymouth so special is all the extraordinary attention it was given before it left the Chrysler assembly line on Dec. 22, 1964. Super Stock Hemi Plymouths for 1965 were available only on a special-order basis from the local Chrysler/Plymouth dealer, and most were ordered by dealers and racers who had “inside connections” with the factory racing representatives. But regular buyers could walk into the showrooms and order these ultra-high-performance machines.

The Lightweight and Powerful RO1 Super Stock Plymouths

The ’65 Plymouth Super Stocks (known as “RO1” cars in dealer sales books) were based on Belvedere I two-door sedan bodies and were stripped down to keep the weight as low as possible. The selling price on these special factory racecars was $4,671, and there was no warranty of any kind. Considering that a regular ’65 Belvedere I V-8-powered, two-door sedan sold for $2,292, you can figure that the Hemi cost more than twice as much as a bread-and-butter version. But if you were after trophies at the drags, it was well worth the extra money.

The Engineering Masterpiece: The 426ci Hemispherical-headed Race Engine

The crown jewel of the ’65 S/S Plymouth is what sat between the front fenders—the special “A990” version of the 426ci Hemispherical-headed race engine. This engineering masterpiece was factory-fitted with all the good parts, so racers just had to add racing slicks and head to the dragstrips. Released in 1964 as a race-only engine, the 426 Hemi also had to be released as a street Hemi to make it legal, but it was not intended for rides to and from the grocery store.

The Superior Breathing and Lightweight Features of the 426 Hemi

Hemis featured a 4.25-inch bore and 3.75-inch stroke, and the blocks were factory-equipped with cross-bolted main bearing caps (No. 2, No. 3, and No. 4). The drag-race engines came with tough, SAE 1046 carbon steel forged crankshafts (tuftrided-treated with eight-bolt flywheel flange); forged connecting rods with beefed beam sections and 7/16-inch rod bolts; impact-extruded 12.5:1 C/R forged pistons (with milled reliefs on the domes for valve clearance); 0.540-inch lift, 312-degree mechanical lifter camshaft; and a double roller timing set. Cylinder heads were fitted with dual rocker shafts, forged-steel rocker arms, and mammoth 2.25-inch (intake) and 1.94-inch (exhaust) valves.

The Intake System and Exhaust Innovations

The design was all about improved breathing, and because Chrysler engineers designed large ports with unobstructed curvatures, the engine’s breathing capacity was like nothing ever to roll out of Detroit! When the first race Hemi was built in 1964, it came with cast-iron cylinder heads. But for the ’65 drag wars, the material was changed to lightweight aluminum. The 426 drag-race Hemi intake system consisted of a two-four-barrel cross-ram manifold that was rather exotic in design. Hemis in 1964 had aluminum cross rams, and for 1965, the material was changed to magnesium, which further reduced weight. Carter carburetors were used in 1964, but for 1965, the engineers switched to a pair of larger carbs, series 4160 Holleys (model 3116A) with 1-11/16-inch venturi bores.

Weight-Saving Techniques in the 1965 Race Hemi

These carbs featured center-hung floats and flowed 770 cfm. There were no chokes utilized on these race carburetors, and separate in-line fuel filters were mounted atop the assembly. Ignition came from a dual-breaker distributor (mechanical advance) that was enhanced by a “transignitor” heat-sink device (Prestolite 201), designed to increase spark capacity. Champion N60Y spark plugs sparked the air/fuel mixture via a set of solid-core ignition wires. Exhaust was handled by a pair of specially built factory headers, which were multi-piece in design and featured cast-steel flanges that connected to the cylinder head ports. Construction details include 2-inch-diameter tubular “tuned” primaries, measuring 41 inches in length, and the pipes were pressed and welded into the flanges.

The Precision of Chrysler’s Super Stock Suspension Packages

On both sides, the pipes were assembled in pairs, with the driver’s side having all four pipes connecting to the exhaust system in a common cluster. The passenger side also incorporated a two-piece arrangement, but the system paired off in two separate flanges to mate with the rest of the exhaust. As a part of the effort to keep the engine light, the ’65 426 race Hemi was equipped with an aluminum water pump housing and aluminum oil pump assembly; aluminum alternator brackets replaced the standard steel pieces. How much power did the ’65 426 race Hemi produce? The factory claimed 425 hp, but dyno testing concluded that figure was on the conservative side. The number was actually closer to 550.

Transmission and Rearend Choices

Transmission choices included a four-speed A-833 New Process unit with Hurst Shifter or a three-speed A727B Maximum Performance TorqueFlite automatic fitted with a manual valve body and high stall-speed converter. In both cases, the rearend housing was the 8-1/4-inch assembly with Sure Grip differential, coupled to 4.56:1 gears. Special drag-race-specific rear leaf springs were fitted to these RO1 cars, and both had a spring rating of 125 lbs, with the driver’s side having six leaves and the passenger side featuring eight.

Additional Weight-Saving Modifications

This design was to best deal with the tremendous torque the 426 Hemi engine developed, and many drag-race aficionados today agree that Chrysler had its act together with its Super Stock suspension packages. Other chassis features included the use of small, 10-inch front and rear drum brakes; the fitting of six-cylinder 0.86-inch-diameter front torsion bars (rather than the heavier V-8 items), designed to promote weight transfer; and in that same spirit, a pair of six-cylinder front shocks was used as well. Weight transfer was a priority, and to add as much weight to the rear of the car as possible, the battery was relocated from the engine bay to the extreme rear of the truck area (right side).

The Subtle but Significant Body Modifications

Rather than use a standard Mopar unit, a hefty 90-amp Super Stock battery was employed. Even though the Belvedere I two-door sedan body was the no-frills model, the Chrysler engineers had a few more weight-saving tricks up their sleeves in creating this true factory hot rod. For the 1965 racing season, the NHRA changed the rules for the Super Stock by not allowing aluminum body panels on current models; only steel could be used. Ever the creative types, Chrysler engineers pulled a fast one and did up the front fenders, hood, and door panels out of special thin sheet metal (0.018-inch thick), weighing less than the standard 0.038-inch gauge steel. The front bumper was also treated to the “diet procedure,” being lightened with thinner-than-stock material (0.040-inch) and chromed to appear like the regular bumpers that adorned other Belvederes.

The High-Impact Racing Look

Inside, most of the frills found in regular production Plymouths of the same vintage were missing. This Super Stocker was built to go fast, not coddle the driver in comfort. The seats were lightweight units, and the windshield and door glass was chemically treated to reduce thickness (and weight) by 0.125 inch. The rest of the glass (rear window, quarter windows, and vent windows) was made of super-lightweight Corning glass, so thin that each side could be pushed and flexed with just a light finger touch. One item that couldn’t be ordered from the dealer was the rather exotic “acid dip” paint treatment that made the RO1 even lighter. Only factory insiders knew about the special pre-delivery “paint jobs” done on these Super Stock cars. In this treatment, the body was dipped in an acid bath and left to soak for some time, with the result being a loss of about 200 pounds!

The Conclusion

Unlike many Super Stock Mopars of the era, this particular car survived its racing career with the original body. This is what makes this Plymouth Super Stocker extra special. Thanks to the meticulous restoration work performed on this historic vehicle, it now looks as if it rolled off the Lynch Road Assembly Plant’s assembly line, ready to be prepped for racing. This Plymouth is truly a testament to Chrysler’s dedication to drag racing excellence in the 1960s.