1969 Pontiac GTO Supercharged - Six Appeal

You really have to hand it to Pontiac chief engineer John DeLorean and general manager Elliott M. "Pete" Estes. In an era when racing was no longer allowed at General Motors, they hardly missed a beat, quickly shifting from factory race cars to high-performance street cars. The pair then fired the opening shot of the musclecar revolution with the introduction of the 1964 GTO. The auto industry would never be the same.

DeLorean was never one to rest on his laurels. His mind always looking forward, John Z. concentrated on developing a performance-oriented Pontiac with European sensibilities and better overall balance combined with a spirited, high-reving six-cylinder.

When this engine made its debut in the autumn of 1965, the 4-barrel-equipped Overhead Cam Sprint Six Pontiac became the first high-performance American six-cylinder engine since the "Twin-H" Hudson 308 of the early 1950s. Displacing 230 cubic inches, the Sprint and its single-barrel low-performance sibling were derivatives of the Chevy six, sharing some basic block dimensions such as bore centers, as well as the crankshaft, crank and rod bearings and some other pieces.

The difference, of course, was the cylinder head and valvetrain. In place of the pushrod-operated valvetrain of the Chevy, resident Pontiac engine guru Malcolm R. "Mac" McKellar developed and refined the design, using a free-flowing OHC cylinder head that featured 1.92-inch intake (same diameter as the 389 and 421) and 1.60-inch exhaust valves. The cam was driven by a fiberglass-reinforced cogged rubber belt that was developed for Pontiac by Uniroyal.

Valvetrain components were also courtesy of Mr. McKellar and originally developed for his extraordinary experimental OHC Pontiac V8s of the early 1960s. The design combined the best attributes of an overhead cam layout with the zero-maintenance of hydraulic lifters. Its secret was the innovative zero-lash adjusters, located in the side of the camshaft cover. Similar in operation to the Pontiac V8s, the plunger section mounted the cam follower, which acted like a rocker arm. Other McKellar touches included a fully-machined combustion chamber derived from the Pontiac V8, a free-flowing intake manifold mounting a Rochester Quadrajet carburetor, as well as a low-restriction, dual-outlet exhaust manifold.

With its large valves and short 3.25-inch stroke, the 230 was a powerful, free-reving mill that was very comfortable at 7,000+rpm. It was rated at 207 horsepower at 5,200 rpm, with 228 lbs-ft of torque at 3,200 and was available in all Tempest and LeMans models, except for wagons.

For the 1967 model year, the OHC-6 gained a few horsepower, up to 215, and availability was extended to the new Firebird line. The lighter, more nimble F-body was an even better fit for the Cammer, as evidenced by Pontiac's own experimental PFST Firebird.

Refinements and upgrades to the original design continued, the most notable being the increase in stroke in 1968 from 3.25 to 3.53 inches, bringing displacement up to an even 250 cubic inches. Horsepower remained at 215 in 1968, though a jump to 230 horses came in 1969 manual trans Sprints due to a slightly hotter camshaft.

Unfortunately, the end of the line for the Overhead Cam Six came at the end of the 1969 model year. Low production volume combined with high manufacturing costs doomed this innovative powerplant. In an era when high-octane gasoline was cheap and 400+ cubic-inch engines ruled the streets, the idea of a high-output six-cylinder was little more than a novelty. Had this engine lasted just a few more years, it would have likely come into its own, its combination of power and fuel economy right in step with the fuel-crunched 1970s.

Brad Nysether of Lake Stevens, Washington is an OHC-6 enthusiast who has added a whole new twist to the mix. The modification of his 1969 Firebird Sprint convertible took a very interesting turn when he decided to see how much streetable horsepower he could wring out of the little inline.

Since his Bird was 1 of only 275 '69 Firebird Sprint convertibles, he didn't want to risk blowing up the original numbers-matching powerplant. With the original mill safely in storage, Brad sought out another engine to begin his quest for power.

A 1968 250 engine was located, purchased and sent to Ed's Automotive, Machine and Dyno Facility in Mukilteo, Washington. Ed Trihey, the owner, performed all development and assembly on the engine himself, as well as all dyno testing. "I remembered these engines from the '60s," Trihey said in a recent phone interview. "We do a lot of supercharged engines, so I was curious about how this design reacted to a centrifugal blower."

The block was bored .060-inches over and fitted with TRW forged pistons intended for a 283 Chevy. A 20cc relief was cut in them to provide a compression ratio of 8.5:1 with the 65cc combustion chambers. Since the production rods and crank are pretty close to bulletproof in stock form, they were rebuilt and new ARP rod bolts were installed for an added measure of safety. A stock replacement oil pump was also deemed suitable and was installed.