Part I: Restoration
The V-8 engine Ford released in 1932 was a watershed design. Though only 10 percent larger than its predecessor, it produced 62 percent more power. But that was just the start. Because it produced that power over twice as many cylinders, it ran smoother. Because Ford arranged those cylinders in a V pattern, the engine didn’t require much more room than the four-cylinder engine that it replaced. And because they needn’t grow much to accommodate the new engine, the V-8-equipped cars went significantly faster.
Of course they didn’t go quite fast enough for some people, particularly an entrepreneur named Robert Paxton McCulloch. A boat enthusiast, McCulloch recognized the potential that Ford’s small, lightweight engine could have in the marine industry if only he could coax a few more horsepower from it. The answer was right at hand. A performance craze captured the go-fast world’s attention in the late ’20s and early ’30s: supercharging.
We’ve all heard someone describe an internal-combustion engine as a pump. In a naturally aspirated application atmospheric pressure fills the void created as the piston descends the cylinder during the intake stroke. Well a supercharger is nothing more than a pre pump: it pushes air into the cylinders at a much greater force than atmospheric pressure. That increases the volume of air that an engine’s cylinders can hold, which has the net effect of increasing that engine’s displacement. What’s more, jamming a greater volume of fuel and air into a given space increases the engine’s compression ratio, which translates to greater efficiency. So not only does a blower make an engine bigger, it also coaxes more power from that increased volume.
The Flathead Ford was practically made for supercharging if only for those two reasons. For one, the Flathead’s intake ports flow poorly. For another, you can’t raise a Flathead’s compression ratio much without compromising its breathing capacity. But a blower overcomes both of those without even touching the engine itself. The reasons why don’t bear explaining here but a supercharged engine also develops less peak cylinder pressure than a naturally aspirated engine that makes the same power. That’s a godsend to a crankshaft suspended by only three main bearings. And a supercharger also makes an engine less sensitive to elevation changes (greater if not full power at higher altitudes).
McCulloch loosely based his supercharger on the centrifugal design built by Schwitzer-Cummins for the Lycoming engines that powered the esteemed Auburn speedsters at the time. Inside it’s basically a fan that spins at such great velocity that it pressurizes the air flowing through it by centrifugal force.
These centrifugal blowers don’t produce very much boost, about 5 psi on a stock engine when all components were new. That’s not a lot by today’s standards but it’s enough to turn a 221ci engine with 6.3:1 compression ratio effectively into about a 280ci engine with about 8.5:1 compression ratio. According to McCulloch’s dyno sheets, that increased horsepower from 85 to 125 (bear in mind that the Flathead didn’t make 125 hp until 1953, and that took 255 ci to get there). In 1939 McCulloch spun the blower even faster to meet the demands of the larger Mercury engine, effectively turning a 239ci engine with 6.13:1 compression ratio into about a 310ci mill with 8.2:1 compression. And that boosted power from 95 to 135, a figure that Ford never achieved with its beloved boiler.
Naturally, McCulloch’s pump proved popular among Auburn fans on Model A budgets, an idea that endures today. Caught up in this mighty wind is our ol’ pal Frank Wallic. You probably remember him from his other exploits, most recently his account in the last issue of how he rebuilt a ’39 Ford transmission. We called him Fearless Frank for his seemingly unflinching courage, but from now on we’re just going to call him crazy.
Not crazy because he bought himself a McCulloch blower. Crazy because unlike almost anyone else who has a McCulloch, he and his pal Gordon Hamilton dared to rebuild his. On the surface it doesn’t seem like a demanding proposition—the only replaceable parts are a few gaskets and seals. And in fact it would be an exceedingly simple rebuild if one just followed the manual. And that’s the problem: Nobody we called knows the whereabouts of such a manual. And among us and our friends we called a lot of people.