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Whipple’s Bigger, Badder & Better Screw Supercharger
By Jeff Smith
Photography: Jeff Smith
A supercharger is the quintessential hot-rod part. It’s that big, polished chunk of aluminum that sits atop an engine and exudes horsepower. The classic GMC-style supercharger is what most hot rodders think about when the discussion turns to blowers, but a new blower on the market now could be a threat to the Roots crown.
Whipple Industries has been quietly selling 12 different sizes of screw superchargers out of its Fresno, California, shop since 1988. Most of these have been tailored toward mild street applications for stock or mildly modified late-model fuel-injected engines. A number of theoretical advantages make the screw supercharger attractive. Foremost is the fact that the screw supercharger is a true air compressor. Roots blowers are aptly named since they blow air, creating boost in the intake manifold by moving more air than the engine can use. Conversely, a screw supercharger actually compresses air as it moves through the mating halves of the screw supercharger. This makes the screw supercharger more efficient than the Roots blower. The improved efficiency means the blower can make more power with the same amount of air because of increased manifold density.
The limitation of the Whipple screw supercharger, until now, was that it was too small to move enough air to make serious horsepower. Combined with a design that required the use of electronic fuel injection, the Whipple was limited to mild-blown applications. But now Whipple has combined forces with the Swedish Lysholm Technologies company to create a bigger screw supercharger that moves more air—a bunch more.
To demonstrate the potential of this bigger screw supercharger, Art Whipple bolted one of the new 2100R, 2.1-liter-per-revolution blowers on a 355 small-block Chevy. Testing took place at Ken Duttweiler’s dyno in Saticoy, California. According to the folks at Whipple, the engine (“Nothing special, just something we had lying around”) is based on a 0.030-over 350 Bow Tie block, a Velasco steel crankshaft that uses Carrillo steel connecting rods, 7.5:1 compression forged JE flat-top pistons and single-moly rings. The heads are a set of Brodix aluminum -8 heads with a midsize 185cc intake port fitted with 2.02/1.80-inch stainless valves. The larger exhaust valve is used to help scavenge the increased cylinder pressure. Valve action is controlled by an Erson hydraulic roller cam featuring 234 degrees at 0.050 duration and 0.510-inch lift for both the intake and exhaust using Erson 1.5:1 roller rockers.
The Whipple blower for this test was bolted to the carb flange of a stock Edelbrock Torker II Dominator intake manifold, which then supported a Carburetor Shop 1050 Holley Dominator carburetor. Completing the engine was a set of Hooker 1¾-inch headers flowing through a pair of Borla stainless-steel 2½-inch mufflers. Ray Zeller of Whipple Industries built the engine and helped with mild tuning while on the dyno.
After the engine was checked out for proper jetting and timing and the 100 octane VP unleaded race gas was added to the fuel delivery system, Duttweiler was ready to pull the handle on the Digilog dyno. We’ve witnessed plenty of blown motors make gobs of horsepower, but this one really surprised us. By the time Duttweiler and Zeller were through tuning, this 355 cranked out a tire-melting 705 lb-ft of torque at 3,900 rpm and an awesome 632 horsepower at a low 5,400 rpm. These are killer big-block power numbers from an otherwise mild 355. While we did not perform a normally aspirated power test, this engine would easily be capable of 425 to 450 horsepower, which means the bolt-on Whipple blower was worth a stout 40 percent power increase.
Looking at the cam specs, a dual-pattern cam and perhaps greater valve lift would have added more power, but the real story is the ease with which the power was obtained. The Brodix cylinder head certainly helped make this awesome power, but the bottom line is Whipple has made a powerful statement with this new 2100R screw supercharger. If nothing else, it will certainly put the screws to your no-power blues.
Whipple also offers a twin-2100R blower system that uses a stock 6-71 supercharger intake manifold. With twin Whipple Chargers on a twin-carbureted 454 with aluminum Dart heads, this engine made 880 horsepower at 12 psi. Whipple’s goal is to make 1000 at 18 psi. The potential here is awesome. Whether you’d ever be able to put all that power to the ground is another question altogether!
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The Whipple Charger 2100R is a very compact supercharger, but it packs a serious punch. A Dominator carburetor mounts directly to the top of the blower. This latest screw supercharger is the same width as previous models but is longer to increase the blower’s capacity to move more air.
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In this partially exploded view, you can see how the intermeshing rotors, or screws, fit in the case. The air is pulled through the carburetor, mixed with fuel and compressed as it squeezes between the screws before exiting through the bottom of the blower into the intake manifold.
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Fully disassembled, the twin screws and drive mechanism are revealed. Extremely close tolerances make this blower a very efficient air compressor. By heating the air less as it’s compressed, manifold density improves, which increases power.
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The Whipple Charger shown here is bolted to an Edelbrock Torker II Dominator manifold. The carburetor sits toward the rear of the blower, but there is plenty of room to clear a normal distributor. The ignition for this test consisted of an MSD 6-AL amplifier, distributor and wires, along with Made For You wire separators.
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Another interesting feature of the Whipple Charger is the serpentine beltdrive arrangement. While this was Whipple’s prototype, the production drive will be similar. Whipple chose to drive everything off a single belt, and it worked well. Whipple will substitute a spring-loaded tensioner for the solid adjustable one used here to help eliminate belt slippage along with a 10-rib drivebelt as opposed to the 6-rib belt used in this test. This test used a 2.6:1 pulley ratio.
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The Whipple Twin-Screw Supercharger Design
A positive displacement compressor
The twin screw supercharger is a positive displacement air mover, in that it moves fixed amounts of air per revolution, like the roots type blower. Unlike the roots however, which is only an air delivery system, the twin screw supercharger is also a compressor. The counter rotating lobes and chambers of the twin screw are designed for a screw-like tapering effect which runs its intake air into a smaller space for output, thus compressing it. The rotors have very close tolerances yet never touch. Compressed air is delivered into the compression environment of the intake manifold with very little leakage or energy loss.
Because of the increased mechanical efficiencies of the superior design, the output air temperatures of the twin screw positive displacement supercharger are radically improved from the roots type. The Whipple twin screw quotes adiabatic efficiency of 70%-80% range across the whole powerband.
As with the roots, since the supercharger is under continual drive, and since it delivers boost practically from idle, overboosting is prevented by the use of an intake bypass system, which allows the engine to breathe normally at cruising or idle: the bypass closes on throttle use, delivering full boost.
Full boost by 2000 rpm
The twin screw supercharger creates boost the instant the throttle is touched, and generally reaches full boost by 2000 to 2400 rpm. Full boost is then available all the way to redline. A positive displacement compressor is ideal for street performance cars or trucks and suv's, and automatic transmissions.
Vehicles used for towing remain very responsive with positive control using this type of supercharger. The instant torque for accelerating, passing, and hill-climbing diminishes the strain on the engine and increases the safety factor. The twin screw compressor is especially useful at high altitude, where physics dictates that all engines lose power, and where our American geography dictates we often take the family vehicle on vacation towing a trailer in heavy traffic.
The twin screw supercharger is essentially silent, producing discernible sound no greater than whisper strength. It has a low profile and generally requires no hood modification. Of all the forced induction systems, the twin screw compressor supercharger is the most obvious for the bootlegger's car, the sleeper, and this is timely in an age where supercharging is no longer just for speed enthusiasts, but for all drivers who have needs for extra power and performance during fairly standard driving conditions.
The Whipple supercharger is the unique twin-screw design that delivers the instant boost at low rpm you expect from a positive displacement supercharger (like the roots type) - but because it's a true compressor it also delivers constant reliable boost throughout the powerband, with none of the fall-off at the higher end, or the fierce heat buildup of the roots, and no waiting for redline to get maximum boost either - it's available on demand, for all situations.
How it Works: Whipple Twin-Screw Operating Principles
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Inlet Phase
The male and female rotor's rotate counter to each other. As the lobes of each rotor travel past each inlet port, air is trapped between consecutive lobes and the cylindrical casing. The air moves axially (forward) throughout the case towards the discharge port. |
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Compression Phase
Once each trailing lobe seals its cell, the air charge is swept around the casing until the leading lobe uncovers the discharge port. At the same time, the male and female lobes will intermesh in such a way so that the volume formed between them, and the apex where the twin cylindrical walls meet, is progressively reduced in an axial direction from the inlet port end to the opposite discharge port end. |
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Discharge Phase
Once equalization of pressure between the existing charge in the manifold and the charge being moved into the discharge port occurs, then any further rotation of the rotors displaces the charge positively into the manifold until the volume between the intermeshing rotors and casing walls in the discharge port region are reduced to ambient pressure again. |
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• Incredibly high adiabatic and volumetric efficiencies
• Positive displacement design
• Very flat efficiency curve combined with positive displacement design gives the most achievable torque of any method
• Instant boost
• A true compressor
• Direct drive from the crankshaft
• Compact and lightweight design
• Virtually silent operation
• Low temperature increases during operation
• Very little power consumption
• Unique combination of low rpm torque and high rpm horsepower due to the screw compressor design
• Have the ability to run from 1 to 60 lbs. of boost
The twin-screw supercharger was originally invented in the 1930's by Mr. Alf Lysholm who was then Chief Engineer of SRM (Svenska Rotor Maskiner AB). The twin-screw design was developed to fill the tremendous voids the centrifugal, turbo and roots superchargers have. This concept was intended to meet the requirements of a high average efficiency under most varied conditions of pressure and speed, a high maximum efficiency - preferable above 85% - with small bulk, low weight and also suitable for direct drive. This concept lead to the development of the twin-screw supercharger which was compact and light, had a very high efficiency over almost all varied conditions of pressure and speed, and an incredibly high maximum efficiency. This concept became a reality in the late 1930's and early 1940's when the Lysholm twin-screw supercharger was produced. Because of high building cost, the screw compressor did not find its way to OEM use on internal combustion engines, but industrial applications for air compressors, refrigeration and air-conditioning.
With technology ever increasing, the screw-type compressors price to manufacture has come down to a competitive level for the internal combustion engines and is distributed throughout North America by Whipple Industries. Art Whipple of Whipple Industries quickly made use of the major benefits of the screw compressor by placing it on the throttle body injected GM 350ci. The results were outstanding, no more turbo lag, no more hot air, just pure power. Since that time, the Whipple Charger has become a household name throughout the performance community for providing the most technologically advanced supercharger kits on the market.
The Whipple Charger creates boost instantly, which gives any motor an instant boost of power. It doesn't matter whether your towing, cruising, or racing, the Whipple Charger gives you the power when it's needed. Because of the Whipple Chargers instant boost, you'll achieve more power throughout the rpm range than any other supercharging method.
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