Paxton-McCulloch Supercharger History - Part I

Paxton / McCulloch Supercharger History – Part I

Robert Paxton McCulloch was born on May 11, 1911, in Missouri. His grandfather, John I. Beggs, made his fortune by implementing Thomas Edison’s electrical powerplants in cities around the world, manufacturing and selling electric trolley cars, and founding Milwaukee’s public utility system. McCulloch, along with his two siblings, inherited his grandfather’s fortune in 1925. This inheritance gave him the financial freedom to indulge in his two passions: engineering and boat racing; he eventually became a national outboard hydroplane champion in classes C and D in the1930s.

Two years after he graduated from Stanford University, he married Barbra Ann Briggs, whose father was Stephen Foster Briggs of Briggs and Stratton. His first manufacturing endeavor was McCulloch Engineering Company, located in Milwaukee, Wisconsin. There he built racing engines for midget racers, and ended up developing a twin-engined, four-wheel drive midget that proved to be so fast it was banned from racing. The search for more speed resulted in further development of engines and superchargers for aeronautical and automotive applications.

The First McCulloch Supercharger
The first product of the McCulloch Engineering Company was a 2-stroke 60 CID 90 hp racing engine developed by Robert P. McCulloch, Gerald C Robechaud and Milton Hoeppner. Another product developed at McCulloch Engineering by Francis L. Colburn was a centrifugal supercharger for the flathead Ford V8. The flathead Ford V8 was an enormously popular power plant at the time, and a low cost centrifugal supercharger developed for this engine had potential for high sales. The resultant supercharger was belt driven, horizontally mounted between the standard intake manifold and carburetor, and may well have been one of the first aftermarket blower systems ever produced.

The McCulloch Engineering flathead supercharger unit was manufactured and sold between 1937 and 1940, and was significantly different to the later McCulloch blow-through centrifugal superchargers in that it was an inline unit, which compressed and mixed the fuel/air charge. It consisted of an impeller, which turned at six times the engine speed in the impeller housing, and was driven by a set of worm gears mounted on the drive shaft and rotor shaft. The worm gears were driven by a triple pulley mounted on an input drive shaft driven from the crankshaft pulley using several belts and were initially lubricated using engine oil under pressure from the engines oil system. By revolving at high speed the impeller caused the fuel/air mixture to build pressure, up to a maximum of four pounds per square inch (psi), within the impeller housing as a result of centrifugal force, and the pressurized mixture was discharged into the inlet manifold. There appears to have been two versions, one without a water jacket, and the other with a water jacket around the impeller housing, which was used to warm the air/fuel mixture and was purported to aid low speed performance. A special three/four belt crank pulley was furnished for the Ford crankshaft, two new water pumps with three belt pulleys, as well as a set of matched V belts, a belt idler pulley and a special air cleaner which was required due to the reduced clearance added by the supercharger. The initial units manufactured in 1937 and retailing for around $85, were designed to bolt onto the existing Ford and Mercury V8s which had the water pumps attached to the cylinder heads. Continuous improvement by the McCulloch engineers resulted in a modified version being introduced in 1938, retailing for $125, and which was also engine oil lubricated via a supplied intake manifold that contained all the necessary connections required for the engine oil lubrication. These also appear to have been offered in water-jacketed and non water-jacketed versions. In late 1939 thermostatic control of the exhaust gas through the impeller housing was introduced in order to promote a rapid warm up of the fuel/air charge output from the blower. These flathead superchargers were designated with a model number that correlated to the year of manufacture along with the intended vehicle application (‘M’ for Mercury and ‘F’ for Ford). Hence the designation 38F referred to a 1938 model intended for a Ford.

The supercharger, which may also have been used as OEM on the Graham-Paige, was purportedly popular with truck owners due to the increased torque and low atmospheric pressure performance that it gave. McCulloch advertising of the period claimed a 38% increase in horsepower, better gas mileage, smoother performance and a longer engine life. More than 5,000 of the superchargers were sold during the late 1930s, but production was discontinued during the early 1940s. This was due to two reasons: the impeller for the supercharger, being gear driven and lubricated via the engine oil system which was often not changed as regularly as it should, had a tendency to become quite noisy with wear; the blower, due to it’s fixed ratio of 6:1, produced no significant boost until high rpm was being achieved by the engine with boost levels being no more than 4 psi, even with radical reworking. These facts failed to impress the general public, and sales were low, although by the early 1940s this had became irrelevant as McCulloch was making superchargers for other purposes, and many thousands were manufactured for military equipment used during the Second World War. In fact McCulloch’s total sales in 1942 were $3 million; the only larger manufacturer in the supercharger field at that time was General Motors.

From Cars to Airplanes to Chainsaws
The success of McCulloch Motors, and the restless nature of Bob McCulloch, resulted in him selling the company to Borg-Warner in 1943 for $1 million, which was subsequently invested in Pan American Airways stock. Six months later some of the stock was sold off and Bob McCulloch set up McCulloch Aviation Incorporated to manufacture 6,000 drone plane engines for the Army Air Force, based upon earlier lightweight two-cycle engines designed by McCulloch. As a result of this contract McCulloch felt that his future lay with featherweight two-cycle engines for Industrial use, and given that it was time for a change, and his current manufacturing facilities were not suitable, McCulloch uprooted McCulloch Aviation and moved it to California.

The move was made in 1946, and Los Angeles was picked due to low manufacturing costs and the availability of skilled mechanics. A fifteen-acre piece of land was purchased opposite the airport and some old barracks set up to serve as offices and plant buildings. As well as Bob McCulloch and his family, a further 33 families of McCulloch Aviation employees made the move to Los Angeles, and as a part of the relocation Bob McCulloch bought 13 houses and 16 apartments to house these employees. Initially during 1946, whilst the 80,000 square foot factory was being built, old barracks buildings were used to house the offices and plant. Many of these had leaky roofs and probably did not create a very good impression when Henry Kaiser arrived with his retinue to enquire about a two cycle automobile motor, however they did serve the purpose and within 60 days of setting up, the first engines (lawn mower and chain saw) were being produced out of these buildings, along with other staple items such as die-cast gas heaters.

The factory was completed in 1946, costing around $1 million, and McCulloch Aviation became McCulloch Motors Corporation, and after evaluation of the product line Bob McCulloch dropped the heaters and development work for the Kaiser-Frazer two-cycle opposed piston engine, and decided to concentrate on the lawn mower and chainsaw engine product lines. These were built by McCulloch Motors Corp. and were supplied to Sears Roebuck and Reed-Prentice respectively, and after extensive research by McCulloch’s engineers (and vice-presidents) John Ryde and Gerald Robechaud, McCulloch found that he could produce a better and lighter chainsaw by himself. As a result of this development McCulloch produced his first chainsaw the 5-49, which produced 5 hp and weighed 49 lbs., two-thirds the weight of its nearest rival, cost $50 less, and sold in such volumes that McCulloch Motors’ 1947 sales of $4 million increased to $40 million by 1951, and a $2.5 million plant expansion was made in 1950.

Click here for Paxton-McCulloch Supercharger History - Part II