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The "Roots" Of Supercharging

A Bit Of Blower Background

In the Beginning
Back in my school days, history was never one of my strong points. Like many of you, auto shop was my main interest and I paid much more attention to that than anything else--well, almost anything else anyway. Now that I'm youthfully challenged I find I'm spending more time reflecting on the past. So when we got together and drew out a game plan for this issue and decided on an engine performance focus, I decided to put some of that reflective effort into investigating the origins of supercharging. With this goal in mind, I retreated to the confines of my office and the wonders of the Internet to delve into the past and see what I could find. I have to admit that upon first glance some of the info didn't seem relevant at first. But as I continued, it kind of all came together. Without further adieu here's some of what I learned. I hope you find it as interesting as I ultimately did.

Way back in 1878 Paris, a gent by the name of Dr. Nicholaus Otto successfully built and demonstrated the first four-stroke internal combustion engine. This development instigated huge interest and spurred others to experiment with, build, and make improvements of their own. By 1896 Rudolf Diesel had filed his first patent for using a supercharger with his compression ignition engine (the first diesel engine), and in 1901 Sir Dugald Clark discovered that if he used a device to artificially increase the volume of air charge entering a four-stroke engine, it produced substantially more power. Right around the same time, back in France, a dude named Rateau developed the centrifugal compressor, and a guy named Renault patented a centrifugal fan, which blew air into the mouth of a carburetor. It was all happening very quickly.

In 1907, back here in the good old U.S. of A., Lee Chadwick, working with J.T. Nicholls, developed the idea of pressurizing an engine's carburetor to increase volumetric efficiency. Initially, they used an 8-inch diameter, single-stage centrifugal compressor driven at five times engine speed by a belt from the flywheel. It worked well beyond their expectations, but like any gearhead worth their salt, they craved even more power. To this end, they decided to install a three-stage blower driven at six times engine speed. The new, improved blower utilized three impellers, each with twelve blades, all of 10-inch diameter but of different widths. This hot-rodded compressor provided three-stage compression, which fed the carburetor with even more pressurized air. Things were definitely starting to get interesting!

In May of 1908, Chadwick entered his car in the Great Despair hill climb in Pennsylvania and won. It's believed that this was the first competitive event in which a blown car was entered, never mind the winner. Over the next two years, the car dominated lots of events, the most notable being the 200-mile road race at Fairmont Park in 1910. Chadwick produced 260 replicas of this car, which had a top speed of over 100 mph, and sold them to the public, making the Chadwick the first publicly available vehicle to exceed that speed. Supposedly, Chadwick had considered an exhaust-driven centrifugal supercharger (that is, a turbocharger) before deciding on the belt-driven type.

Meanwhile, back in Europe, in 1911 and 1912 Sizaire and Birkigt, again in Paris, were experimenting with centrifugal blower- and piston-type compressor designs, as well. Birkigtt designed a Hispano Suiza-based engine, which used two of its six cylinders to supercharge the other four. That is, essentially a four-cylinder engine with a built-in two-cylinder compressor for supercharging. From what I gather, that experiment wasn't very successful.

Aviation Realizes the Benefits of Supercharging
During the course of World War I, supercharger development went a lot further with its use in aircraft engines in the continuous attempts to gain altitude for early fighters and bombers. Initial developments centered on the "Roots"-type positive displacement blower, but the potentially more efficient centrifugal compressor quickly replaced this. Because of the need for the high speed of the compressor, step-up geardrives had to be used. There were a lot of problems with these early systems, mainly due to rotational inertia. Spring drives, flex drives, fluid couplings, and centrifugal clutches were all tried at one point or another.

The main line of development of aircraft superchargers in Europe continued with mechanical drive. The Rolls Royce aircraft engine set the trend for a long line of engine developments by using a three-speed gearbox system to drive a two-stage centrifugal supercharger. In the Americas, the use of geared centrifugal compressors for aircraft engines was altered around 1925 as a result of General Electric's development of a practical turbocharger.

Back to the Blacktop
Following a lapse of 12 years since Chadwick's work back in the United States, the Duesenberg engine appeared in 1924 and won the Indianapolis 500 race. It had a two-litre engine with a centrifugal compressor, installed with the impeller at right angles to the line of the crankshaft. This was the first supercharging system to suck air through the carburetor, and subsequently showed an improvement when compared with positive displacement blowers, due to fuel cooling. There also began the widespread use of alcohol fuels in racing. With the exception of Mercedes, who persisted in downstream carburetor positioning until 1937, the practice of mounting the carburetor in front of the supercharger became normal.

From 1925-38, the Grand Prix formula led to the supercharging of virtually all racing engines; there was a steady increase in power, coupled to increased boost pressures and the use of alcohol fuel. By 1938-39, Grand Prix racing was completely dominated by the enormously powerful Mercedes and Auto Union cars. The Auto Union contender had a six-litre engine delivering 520 hp at 5,000 rpm, running on methanol fuel, with a compression ratio of 9.2: 1, and a boost pressure of 1.8-bar. The Mercedes M125 produced 646 hp. Both Mercedes and Auto Union used two-stage supercharging with Roots blowers, and in 1939 were getting up to 2.65-bar pressure on three-litre engines.

After World War II, when European racing finally resumed, Formula 1 Grand Prix was 4.5 liters un-supercharged or 1.5 liters supercharged, and many of the pre-war supercharged designs competed successfully. In 1950-51, the non-supercharged Ferrari engine became dominant and the decline of the supercharged cars started. The only significant attempt to continue with supercharging came with the ill-fated V-16 BRM car, which used a Rolls Royce aircraft-type, two-stage centrifugal supercharger. At 5,000 rpm, the 1.5-litre engine produced only 100 hp, but at 8,000 rpm it jumped to a more than respectable 330 hp, backed by a similar, rapidly rising torque curve--a combination that must have made it quite a handful to drive!

The period between the two World Wars was the heyday of supercharging. Not only did the major racecars of the time run blowers but, as you might expect, so did several of the more racy production models, both here and in Europe. However, the economic Depression and then WW II finally put an end to supercharged luxury sports cars and, shortly after war's end, the changing of rules put a stop to the supercharger's advantage in racing. Consequently, after the 1940s, superchargers virtually disappeared from the automotive scene.

Leave it to the hot rodders
It was just before and after World War II that hot rodding really began to exist. The youngsters who raced stripped-down Model Ts and As on dirt ovals and dry lakebeds were a far cry from the sophisticated European Grand Prix and U.S. Indy race car builders. But they'd been paying close attention to the way the pros built race engines and they knew superchargers made horsepower. In the hot rodding world there was no restriction on blowers; the major hurdle then was cost.

Even though, there were still a few early examples of blowers being run on the lakes, even in the Depression days before the war. A few rodders snagged centrifugal blowers from production American cars like the Graham, and adapted them to the Ford flathead V-8. However, Graham blowers produced meager boost and when anyone tried to spin 'em faster to get more pressure they usually ended up tearing up the blower's drive gears. Around that time McCulloch introduced a centrifugal supercharger as an aftermarket bolt-on kit for the Ford V-8 (most likely the first aftermarket blower kit), and some of the more bucks-up builders tried them at the lakes.

The first example that I found of a Roots-type blower being fitted to a hot rod was in the late '30s when the Spalding Brothers scoffed up a Mercedes Benz blower and put it on their flathead Ford. After the war, Don Blair bought this blower from the Spaldings and adapted it to his unlimited-class roadster for the 1946-47 seasons. Running alcohol through two Stromberg 48s, and driving the blower with two V-belts--the car turned 141 mph.

The person usually credited with the first installation of a Jimmy (GMC) blower on a hot rod was Barney Navarro. Barney had been aware of blowers for some time, but they were scarce and expensive. Then one day in 1948, Kong Jackson showed up with a 3-71 GMC off a World War II landing craft, and offered it to Navarro for $60. Barney was manufacturing his own line of V-8 heads and intake manifolds at the time, so he modified one of his manifold patterns to fit the blower and cast an intake manifold for it. He built his own drive using four V-belts and mounted four Stromberg 48 carbs on top of the blower to run alcohol through a de-stroked, 176-cube V-8 in his '27 roadster. This setup made around 16 pounds of boost and pushed the car to 147 mph. The only internal modification that Barney made to the blower was to bore the case slightly larger for increased rotor-to-housing clearance so he could really wind it out.

Barney not only ran the roadster at lakes, but also raced it on the dirt circle tracks, possibly the only supercharged hot rod to do so. And though he never had any serious mechanical problems with the blower itself, the V-belt drive drove him nuts since they had a tendency to heat up and disintegrate. Barney finally overcame this malady by drilling a bunch of holes through the pulleys to help keep the belts cool.

Tom Beatty, who worked for Navarro, built a similar system for his own lakes roadster, adapting a 4-71 GMC to an Oldsmobile OHV V-8 for his belly tank lakester. Beatty eventually manufactured manifolds and drive "kits" for the Jimmys, based on the Navarro V-belt design, and helped pioneer the more widespread use of GMC blowers. In fact, Beatty once stuffed one of his blown race engines into his '40 Ford sedan delivery to use as a street driver and push truck.

Supposedly, Navarro was also one of the first to run a blower at the drag races, since he entered his roadster at the first running of the Santa Ana drags in 1950. However, Barney did not pursue drag racing with a blown engine because he kept blowing quick changes to pieces.

Into the '70s and Beyond
As far as supercharging for the majority of street cars are concerned, the history is rather brief. After the prestigious supercharged road cars of the '20s and '30s, the next appearance of blowers was a handful of bolt-on supercharger kits that suddenly appeared on the market about 1950. These included the McCulloch, the Frenzel, the S.COT/Italmecanica, a few assorted blower kits based on reworked GMC 3-71s or 4-71s like the J.E.M. and Speed-a-Motive offerings, and later the Judson and Latham superchargers. Then, in the mid-'50s after Chevrolet introduced its new small-block V-8, Ford and other manufacturers suddenly found themselves in the position of playing catch up. Since Ford's new V-block was no match for the Chevy, Ford turned to supercharging as one way to beat those darn Chevys on the NASCAR tracks and on the beach at Daytona. They recruited McCulloch to design a special centrifugal blower for the racing Fords, and then offered the standard McCulloch variable-speed, belt-driven blower as optional equipment on '57 Fords and T-Birds. The same year Studebaker offered the McCulloch on their Golden Hawks and on some of the last Packard models. As late as 1963, the McCulloch/Paxton was used as standard equipment on the Studebaker Avanti.

From this time on, however, Detroit turned to the turbocharger for supercharging production models. Through the '60s and early '70s, there were isolated examples of supercharged street-driven hot rods, but most of these were way out of the norm. The sight and sound of a working GMC blower on the street, not to mention the potential power they provided was exciting to say the least. But GMC blowers were scarce, parts to adapt them to a street engine were nearly non-existent, and getting one to work right in traffic took lots of trial and error.

Within the last couple of decades, however, blowers have come of age for street machines. People have discovered that, with proper clearances, bearings, and drive ratios, there is no reason why a Roots-style blower should be any "hassle" on the street. First, a variety of companies offered complete drive kits for Jimmies on street motors--which incorporated water pumps, fans, alternators, and so on. Then, a couple of companies started fabricating or modifying blower manifolds to fit street motors other than small-block Chevys and Hemis. Heck, these days you can choose from a variety of complete bolt-on street-blower kits, including polished and ready-to-run blowers, manifolds, drive assemblies, carbs, and everything else you might need. In addition, several companies have recently introduced new superchargers and installation kits designed specifically for street performance engines--many designed to work directly with today's electronically controlled fuel-injected engines, producing big power gains with virtually no other engine modifications. And finally, with advances in design and efficiencies, we are seeing factory/OEM availability of belt-driven superchargers for the first time since the 1950s. Supercharging is indeed alive and well.

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