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.
Wallic did have one asset: Bart Grange, a friend with an intact McCulloch. He disassembled that blower and measured every critical tolerance. Then he and Hamilton rebuilt his blower to those specs.
The absence of service parts didn’t seem to interfere: the consumable items consist of universal shaft seals that Wallic bought from his local bearing house and paper gaskets that he made from magazine pages and covers. He made only one part, a thrust bearing, which he reproduced with a brass washer. His were good but the plain bearings would be easy to reproduce by just about any machine shop. Beyond that there are no other wear parts to replace beyond gears, the rotor, shafts, and the case castings. And even if those parts were still available it would still probably make better economic sense to find a better blower to rebuild rather than try to buy replacement parts.
We contributed another asset to the knowledge pool: good pal and Early V-8 Club member Alan Darr. A collector of outstanding note (see his Gilmore collection in the first Street Rodder Premium), he snapped up the few pieces of rare McCulloch literature that came his way over the years. Among them are a schematic and a series of technical sheets that show part numbers for the ’39 Ford blower which is internally identical to Wallic’s ’39 Mercury blower.
These sheets don’t reveal assembly instructions but they do give us pause to wonder if the blower Wallic referenced matches McCulloch’s specifications. For one, the schematic shows shims (gaskets) in places where there were none in the reference blower. For another, the thickness of a number of gaskets in the reference blower differs from the thickness that McCulloch’s literature calls out. That McCulloch specified 0.002- and 0.003-inch-thick gaskets indicates that it was concerned with precision down to 0.001-inch. That’s critical knowledge as McCulloch used gaskets as shims to set critical tolerances just as Ford did with its early rear axles.
It could very well be that the reference blower is still right at (or at least close to) McCulloch spec. But it could just as easily be out of whack. So understand that the information we’re going to dispense here isn’t gospel. It’s just the best we have.
But to be fair, the best we have seems to work so far. Wallic has since installed his blower on the engine in his roadster. Though he hasn’t had the opportunity to flog it for miles on end he says he definitely feels a bit more power and so far neither the blower nor the engine has complained. Fingers crossed, this could be it. At least we’re a little closer.
The information Darr’s literature reveals would take too much space to address properly in one installment. So for that reason we’re going to divide the story into tentatively two parts: this one to show the basic rebuild and another to shed some light on the way the literature suggests these parts install on the engine.
We say tentatively because we’re hoping that this story rattles loose some more vital information that could lead to additional installments. In fact we’re going to make the same challenge to you that Wallic made to us: We bet you can’t turn up any more information. We dare you to prove us wrong, if only so we can expand the knowledge.
So have at it: show us some literature that shows us how right or wrong we really got it. Until then, take a rare look inside a rare specimen.
Special thanks to Frank Wallic, firstname.lastname@example.org.