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July 2013 Vintage Vault - Supercharged Mule

Posted in Features on June 12, 2013
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(Editor’s note: While scouring the Source Interlink Media archives, we stumbled across this gem originally published in the Feb. ’55 issue of Car Craft magazine. Enjoy.)

Perhaps the most versatile and rugged little hunk of road machinery ever designed was Truck, GP, otherwise known to the world as the Jeep. Versatile though it is, however, there are a few places where the little beast, as it comes from the Willys factory, can’t go.

This latter fact was somewhat distressing to a Los Angles gent, Vic Hickey by name. Vic loves Jeeps; he also loves to head for the High Sierras on hunting and fishing expeditions, and the Sierras have a few spots where even a subnormal mule won’t go.

Hickey, who owns an automotive engineering firm, decided to see what he could do about the situation. After considerable pondering, he came up with a set of very marketable dual-wheel adapters which gave the little Jeep a somewhat spraddle-legged appearance, but also laid enough rubber on the ground to enable the thing to scrabble up a brick wall.

All this traction, however, begets a need for more power to pull it. Vic rose to the occasion and designed a head with a combustion chamber allowing compression ratio boosts up to and above 8:1. Such is the nature of the beast that compression ratio can also be dropped from a normal 6.48:1 to a low 5.5:1, the reason for which we’ll see in a minute.

First he tried a 7.75:1 head plus a dual carburetor Burns manifold mounting a pair of Ford glass-bowl Holleys. The ports were reamed out to 1.658 inches and the valves narrowed by undercutting. A Potvin road cam was installed and the valve springs shimmed 0.100-inch. In this first engine, the stroke was left stock but the bore was increased by 0.080-inch. With this conversion the Jeep was able to attempt and conquer the hill in the title illustration.

One thing about Hickey though—he’s never satisfied. This time he tore into the engine after even more horses. The bore was punched out another 0.020-inch and the stroke increased to 45⁄8 inches, Jahns solid skirt pistons were installed and the compression was dropped to 5.5:1.

The compression drop was for good reason. By this time Vic had managed to latch onto a 3-51 GMC Diesel supercharger. This formidable piece of machinery was adapted to take a Carter carburetor designed for the Chevrolet Corvette. A sheet steel and tubing manifold was made to adapt the blower to the Jeep block. A split exhaust manifold was also built to replace the stock system he had used until this time. One-third of the weight of the iron flywheel was milled off and adapter to take an Auburn clutch that was beefed up to be even stronger than the original unit. A fixed-advance Wico magneto was installed in place of the battery igniter. Since the stroker pistons were a shade long, Vic left the top compression ring off in order to clear the gasket and not burn the ring. Despite pumping eight pounds of boost, Vic says he has no trouble with this setup. Blower speed is one and one-half times engine speed.

Only one problem presented itself during the conversion. This was the matter of gaining bottom pulley clearance between the engine and the front wheel drive unit. The problem was simply solved by redrilling the center bolt holes in both front springs and moving only the axle, not the spring, forward exactly the distance that the center bolts were moved. The only change this necessitated was adding the extra 11⁄2-inch to the front driveshaft, as shown.

Hickey clams a full 90-horsepower at the rear wheels in two-wheel drive and high transfer. There’s no way of telling, unless someone builds a four-wheel drive chassis dynamometer, just what is being pumped through in full drive and low transfer. Whatever it is, it’s enough to send this former Army mule off the line like a dragster. It’s also enough to take Vic just about any place he dares to go. But is this the ultimate? We’ve known Vic and his Jeep for more than two years now, and each time he surprises us. We won’t even venture to predict what he’ll do next, it’s too risky and it’s been tried before without success. Not only that, but all seven of Hickey’s crew in the shop cooperate on these projects. Who knows what seven guys will come up with?

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