For decades, engineer Malcom “Mac” McKellar spearheaded the Pontiac division’s advanced engine development team, and one of his favorite projects was this overhead-cam version of the 421 cubic-inch V8.
In the early ’60s, the engine program at the Pontiac division of General Motors was a wide-open operation that bustled with innovation. Under the leadership of chief engineers Pete Estes and John DeLorean, Pontiac engine guru Malcolm “Mac” McKellar (1920-2011) and crew developed the Super Duty 389 and 421 NASCAR engines that embarrassed the Fords and Chevrolets at Daytona. Their outside-the-box approach also produced creative solutions like the OHC 6 and the half-a-V8 Tempest four. (Read about the Tempest slant four here and the OHC 6 here.)
Along the way, there was even a series of trick Pontiac factory racing camshafts that were named after McKellar—McKellar number 7, number 10, and so on. But it appears that McKellar’s proudest creation in his years at Pontiac, even though it was never approved for production, was an innovative single-overhead-cam version of the Pontiac 421 cubic-inch V8—a fascinating project that needs a closer look.
The program’s first prototype engine, interestingly enough, was a four-valve, four-cam V8 completed early in 1963 (above left). Massive, complicated, and sporting cross-ram fuel injection, this 389 DOHC V8 soon led to a more streamlined approach, including the production-based SOHC V8 shown at upper right. To improve packaging, the Pontiac crew experimented with both front and rear-mounted camshaft drives, and also with conventional roller chains and a brand new development, the fiberglass-reinforced toothed timing belt. Up to that point, the only production car to use the belt was Glas, a small German carmaker that was acquired by BMW in 1966. Once it was tried, the belt became a standard feature of Pontiac’s OHC V8 experiments.
McKellar and crew also tried a wide range of valve arrangements with two, three, and four valves per cylinder. It’s fascinating to note that McKellar’s three-valve experiments included both possible configurations: two intake valves and one exhaust, and one intake valve and two exhaust. (The latter used a massive 2.228-in intake valve.) But eventually, the project settled on a more conventional combustion chamber layout with two valves per cylinder and generous squish/quench zones. These heads were mated to block castings that were closely based on the production Pontiac V8, and sometimes used production intake and exhaust manifolds.
If you’d like to know more about McKellar’s ideas and experiments with overhead-cam V8s, fortunately they were captured at length in a cover story in the March 1968 issue of Hot Rod magazine, below. (That’s him on the cover with a roomful of experimental Pontiac engines.) As we know, the overhead-cam V8 never made it into production, as the the Pontiac brass could never find a business case for it. But the McKellar team’s design, including the valvetrain layout, hydraulic valve lifters, and timing belt drive, were lifted nearly intact and used on the OHC 6, which Pontiac produced from 1966 to 1969.
Tom Nell picked me up in a 69 Grand Prix for a meeting with Arnie Beswick at a car show in Detroit. The first thing I noticed when he pulled up was piston slap at idle. Asking him what was up, he popped the hood to reveal this engine. Tom never got on it during our drive, so have no perspective on its performance, but I did get to ride behind one.
What a great story, thanks.
Mickey Thompson won the NHRA Top Eliminator with a Pontiac Hemi (he made the heads). 1964 think.
Yes indeed. M/T’s Pontiac Hemi was very similar to the 427 Ford Hemi he also produced. We have a feature on it. https://www.macsmotorcitygarage.com/mickey-thompsons-427-ford-hemi-v8-and-its-fascinating-secret/
C. 1964, everyone’s tongue was wagging about the new (Gen II, in today’s parlance, and ‘TM”) MoPar Hemi but Pontiac fans knew that it would not have had the races all its way if GM hadn’t taken the biggest, best financed engineering plant out of racing! Until FoMoCo ramped up, it was like letting a randy barbarian loose in a nunnery, both on the speedways and at the drags. Pontiac and Chevy, what racers were left, were trying to compete with worn and obsolescent cars — and the rest was history. I don’t argue the 7-litre limit, but head design isn’t exclusive; and Chrysler didn’t invent the layout, either. No, Mac had laid his plans, but it was not to be! Another HRM cover had the revived Olds cammers; the mind boggles!
It’s an honor to have you reading and commenting here.
Chrysler didn’t invent the hemi head layout, but they DID productionize it in 3 flavors for a decade!
The OHC Six was nice engine but only lasted 3 years. Never have seen one that came with a 4 bbl carb. The rest wee all hi-hum 2bbls.
1 bbl you meant.
The rest were all ho-hum 2bbls.
I had a 1958 bonnieville convertable and it would not start when engine was hot
The eternal counterweight of finance eventually won the day at Pontiac. When the -670 and subsequent 2nd Gen cylinder heads could produce most of the power gain for a fraction of the cost… that was that. Beyond the cost and manufacturing complexity was the questionable corporate judgement of loading even more power into cars that were marginal on their best day. Smokey Yunick referred to a few of the projects, including the 4-cam as “rich kid killers.” The oval tracks of the day felt the spillover, as the Mystery V8, Hemi and High Riser were overpowering the tires and chassis hardware of ‘stock’ cars, taxing the skill of the drivers under enormous pressure to win. The idea of today’s high performance schools for drivers to prepare for the race car reflexes of Corvettes, V-Series and others was a pipe dream.
The very obvious,, how much more power did these engines make over normal 2 valve pushrod engines?? Little if any as has been proven. And making a better head for a pushrod also could be done.
Look at those pics and that 4 cam engine is huge [a bit like the modern Ford] and would simply be a fitment issue in a real car. The single OHC engine would need the [heavier] engine pushed forward so again a fitment issue. And car balance issue.
Pontiac V8s were all quite heavy to start with. Most solid performers but heavy.
Compare that with the SBC and power per pound makes the SBC a clear winner.
MacMckellar was given this engine installed by Pontiac installed in a Grand Prix for a retirement gift. I wonder what happened to that Grand Prix?