This comparison strips the crutches away and looks at the superchargers on their own. No intercooling, no fuel through the blower, same engine, same rpm, same cell. That makes the real difference easy to see: boost alone does not tell you what the engine is getting. Air density does. The 10-71 Roots made the number on the boost gauge, but it heated the air hard and gave up efficiency as speed climbed. The 5.0L Whipple screw blower delivered denser air at similar boost, ran markedly cooler, and improved compressor efficiency as rpm increased. That means more oxygen in the cylinder, less wasted heat, and more power potential from the same basic pressure. It also took less out of the crankshaft to drive. At matched horsepower, the Whipple used far less fuel. At matched fuel flow, it made substantially more horsepower. That is the difference between making boost and making quality boost. If you care about throttle response, usable airflow, and how much power actually reaches the flywheel, the screw supercharger is the clear winner here. Banks iDash was used to log the data that made that obvious.
Gale Banks introduces a new 5.0-liter Whipple screw supercharger and frames the episode as a direct comparison against the 10-71 GMC Roots blower he had previously destroyed. The earlier blower failed because it was run dry, without fuel passing through it. Banks notes that many racers run fuel through 71-series GMC-style blowers partly to mask how much heat those blowers add to the air. In this test, that crutch is intentionally removed. Both superchargers are evaluated dry on a diesel engine so the comparison reflects the blowers themselves rather than any fuel-cooling effect.
The diesel platform is central to the method. Because a diesel has no throttle plate, airflow is not restricted on the way into or out of the supercharger. Engine speed and load are controlled by fuel quantity alone: adding too much fuel can kill the engine, while reducing fuel brings it back toward idle. Banks uses the engine as a controlled test bench, keeping the same engine, RPM points, dyno cell, operators, and general setup for both tests. The only meaningful variable is the supercharger. The 10-71 had been run at 20 percent over crank speed, and the Whipple was adjusted to produce roughly equivalent boost so the two could be compared under similar operating conditions.
Banks emphasizes that boost pressure by itself is not the real measure of supercharger performance. In his view, boost is mainly useful as an intermediate value for calculating air mass flow and air density. What matters to the engine is how much air mass is actually being delivered, because horsepower comes from mixing fuel mass with air mass. The key metric is air density per cubic foot, not simply pressure.
That distinction drives the entire comparison. Two superchargers can show similar boost numbers while delivering very different air quality. A more efficient blower can move denser air at the same nominal boost, which means more oxygen available for combustion and therefore more power potential. Banks repeatedly returns to this point: the meaningful engineering question is not who makes the bigger boost number, but which compressor delivers the greater air density with less heat and less parasitic loss.
Before returning to the dyno data, Banks explains how the two superchargers differ mechanically. The 10-71 GMC is a Roots blower. Air enters through the top, then is carried around the outside of the case by meshing rotors and pushed into the intake manifold. It is fundamentally an older positive-displacement design that moves air but does not internally compress it in the same way a screw compressor does.
The 5.0-liter Whipple is a screw supercharger. Air enters from the rear, and the male and female rotors thread together and progressively squeeze the air forward before discharging it through a triangular outlet at the front bottom. Banks compares the process to squeezing toothpaste from a tube. He briefly places the design in historical context, crediting Alf Lysholm, who patented the screw supercharger in 1938. Banks notes Lysholm's work in Europe before World War II, including applications on locomotives, aircraft, ships, and submarines, and then his later work in the United States with the Navy. The point of the history lesson is that the screw design is not new, but it represents a more advanced compression method than the old Roots architecture.
The first focused comparison is made at 3,200 RPM. Banks chooses this mid-range point because it reflects where the engine has been operating and provides a useful basis for comparing the two blowers. In this test, the goal is to match the horsepower previously achieved with the 10-71 and then examine fuel rate and supercharger performance.
At 3,200 RPM, the 10-71 produced 12 psi of boost, while the Whipple produced 14 psi. Although that is only a 2 psi increase, Banks says the more important result is the change in boost air density. With the Roots blower, boost air density was 22 pounds per thousand cubic feet. With the Whipple, it rose to 35 pounds per thousand cubic feet. That 13-pound-per-thousand-cubic-feet increase represents a major gain in usable air. Banks estimates that amount of added density is worth roughly 100 horsepower on diesel, and a little over 130 horsepower on gasoline, even before considering other effects.
Manifold air temperature shows another major difference between the two compressors. At 3,200 RPM, with no intercooling in the system, the Whipple produced a manifold air temperature of 265 degrees, while the Roots blower reached 325 degrees. Banks points out that the Roots was therefore 23 percent hotter at that operating point. Looking farther up the speed range at 5,000 RPM, the Whipple measured 295 degrees while the Roots reached 426 degrees, making the Roots 44 percent hotter.
Banks deliberately avoids intercooling during this phase of testing because he does not want the intercooler to influence the compressor comparison. An intercooler changes outlet conditions, and if the cooling medium varies, especially in a liquid-coupled system, it can alter the apparent performance of the supercharger or turbocharger being tested. By leaving intercooling out, he isolates the blower's own thermal behavior. He also notes that he has been using intercooling for decades, so the absence of an intercooler here is not philosophical; it is simply necessary for a clean engineering comparison. His conclusion from the temperature data is straightforward: as speed rises, the Whipple remains comparatively controlled, while the Roots blower's heat output escalates sharply.
Banks then turns to compressor efficiency, which he considers the bottom-line metric. He prefers to generate his own efficiency numbers rather than rely on published compressor maps, and he mentions that future versions of his iDash and DataMonster instrumentation will display compressor efficiency directly.
The Roots blower performs best at very low speed and then deteriorates as RPM rises. At 1,000 RPM crankshaft speed, the 10-71 is a little over 65 percent efficient. By around 2,500 RPM it has fallen well below 50 percent, nearly touching 45 percent. At the 3,200 RPM comparison point, it is 50 percent efficient, and by 5,000 RPM it drops to 48 percent. Banks summarizes this behavior by saying the Roots is best when you do not need it and worst when you do.
The Whipple follows the opposite trend. At 1,000 RPM it is only about 38 to 39 percent efficient, but by roughly 2,500 RPM it climbs into the mid-60 percent range. At 3,200 RPM it reaches 68 percent efficiency, and at 5,000 RPM it improves further to 71 percent. Relative to the Roots, that makes the Whipple 36 percent better in efficiency at 3,200 RPM and 48 percent better at 5,000 RPM. Banks argues that this translates directly into denser air entering the cylinders, which is what produces stronger combustion and better real-world response.
Banks challenges the common assumption that a traditional Roots blower automatically delivers the best throttle response. He argues that if added air density is what creates added power, then the Whipple's superior density curve suggests it should outperform the 10-71 in response as well. On the boost air density chart, both blowers begin at roughly the same point near 1,000 RPM, around 4 pounds of additional air per thousand cubic feet. From there, however, the Whipple quickly pulls away.
At 3,200 RPM, the Roots produces 22 pounds per thousand cubic feet of boost air density, while the Whipple produces 35 pounds per thousand cubic feet. That makes the Whipple 59 percent better at that speed. Banks describes the area between the two curves as added power available from the screw design over the Roots design. He ties this back to his instrumentation philosophy, arguing that boost air density is a far more useful gauge than boost pressure alone because it incorporates the effects of efficiency and temperature. He also warns that simply increasing pulley ratio and chasing a bigger boost number can make a vehicle slower if the supercharger is pushed beyond its efficient range, causing heat output to rise and compressor efficiency to collapse.
The second major dyno comparison holds fuel flow constant instead of horsepower. The target is the same fuel consumption used by the 10-71 test: 97.5 pounds of fuel per hour. Banks says this is where the difference becomes profound because the power required to drive the blower comes directly off the crankshaft. Any reduction in parasitic drive loss means more of the engine's produced power reaches the dyno, the wheels, the water, or the track.
He summarizes the baseline 10-71 result this way: the temperature increase across the blower was 219 degrees, and the engine consumed 97.5 pounds per hour of fuel to make 177 horsepower. In the first Whipple run, where horsepower was matched at 177 horsepower, the temperature increase across the supercharger dropped to 176 degrees and fuel consumption fell to 77.8 pounds per hour. That is nearly 20 pounds per hour less fuel to make the same power, which Banks characterizes as roughly a 20 percent improvement in fuel economy.
Then, in the constant-fuel-flow Whipple run, the fuel rate was brought back up to match the 10-71's 97.5 pounds per hour. With essentially the same boost and the same 176-degree temperature rise across the supercharger, horsepower jumped to 235. That is a gain of 58 horsepower over the Roots blower at the same fuel flow. Banks attributes that increase to the lower parasitic loss of the Whipple compared with the 10-71.
Banks concludes that the 5.0-liter Whipple decisively outperformed the 10-71 GMC Roots blower in every meaningful category of this test: lower manifold temperature, higher air density, better compressor efficiency, lower fuel consumption for the same power, and substantially more horsepower at the same fuel flow. He argues that the result is not even close. The Whipple delivers higher-quality boost while also taking less power from the crankshaft to drive it.
He also notes that this comparison only covered the 1,000 to 5,000 RPM range for blower evaluation, and he expects the gap to widen as operating conditions become more demanding. In his view, the Roots blower will continue to lose efficiency and consume more power, while the Whipple will continue to improve within its operating range. He adds that turbocharging may ultimately prove even better in parasitic terms, but for this project he wants the strong throttle response associated with a positive-displacement supercharger. Based on these results, he believes the preferred supercharger for the build has been identified. The next step is to add intercooling and continue the development program.