We lit the supercharged 7.0L Duramax and got the answer fast: this roots blower can make pressure, but it makes too much heat doing it dry. At 5,000 rpm, the 10-71 produced a little over 18 pounds of boost, but manifold air temperature climbed to 423 degrees. That matters because the engine does not run on boost numbers. It runs on air density. With that much heat, the pressure increase did not translate into the oxygen gain you would expect, and the blower’s measured compressor efficiency landed at 48%. That is the real problem with this kind of blower in this role. It moves a lot of air, but it also takes serious crankshaft power to drive and adds enough heat to wipe out density. Compared with the turbocharger efficiency model used here, the roots blower gave up both airflow and horsepower while demanding parasitic drive power from the engine. If we are going to keep the blower for low-speed response and still push this super-turbo plan forward, we have to beat the heat first. That is why the next step is adding cooling instead of pretending the boost number tells the whole story.
The video opens with the start of a Duramax super twin-turbo development program. The engine is a 7.0-liter Duramax fitted with a BDS 10-71 Roots blower, Wagler cylinder heads originally supplied for a dragster project, and a custom camshaft profile from Comp designed for this combination. The intended operating range is 5,000 to 6,000 rpm, although the initial testing is limited to 5,000 rpm. The immediate goal is to measure the blower's parasitic load on the crankshaft and determine how much heat it adds to the intake charge through compression.
The induction system uses two large L5P air filters and two 4-inch mass air sensors, giving the setup enough metering capacity for up to 120 lb/min of intake airflow. Fuel supply comes from two Bosch high-pressure pumps driven at 80 percent of engine speed, or about 20 percent under crankshaft speed. The blower itself is overdriven by 20 percent, so at 5,000 engine rpm it turns 6,000 rpm. The engine also uses a full dry-sump oiling system adapted from a previous road-race GMC truck project.
After startup, the team confirms that the engine lights off cleanly and begins warming it before making any pulls. Oil pressure and coolant flow are checked, and the discussion turns to the oil-cooling arrangement. The engine appears to be based on an earlier Duramax block architecture, likely LMM or LML based, but it uses a 2020 L5P engine oil cooler. The dry-sump oil is routed through that cooler so the engine can remain self-contained rather than relying on a remote-mounted cooler elsewhere in the vehicle.
That packaging choice is part of the broader experimental nature of the project. The aim is not only to build a functioning supercharged diesel, but also to document behavior that has not been well characterized on modern diesel platforms such as the L5P Duramax, Cummins, or Ford applications. With the engine warmed, coolant circulating, and thermostats open, the team begins data logging and prepares for unloaded dyno sweeps to isolate the blower's behavior.
The first meaningful test is performed at 3,200 rpm with essentially no engine load other than what is required to spin the supercharger and satisfy the dyno's minimum horsepower demand. At that speed, the dyno requires roughly 90 hp just to operate. Intake air temperature entering the blower is measured at 94 degrees Fahrenheit, while discharge temperature climbs to 296 degrees Fahrenheit at about 11.8 psi of boost. Even before the full sweep, that temperature rise is alarming.
The team then continues gathering data from 1,000 rpm through 5,000 rpm, recording boost and blower discharge temperature at each point. By 4,000 rpm the discharge temperature is already around 330 degrees Fahrenheit, then 350 degrees, and by 5,000 rpm it approaches 400 degrees. The run is stopped when the measured compressor discharge temperature reaches roughly 423 degrees Fahrenheit. That result immediately suggests the dry Roots blower is generating far more heat than expected for the amount of boost produced.
Gale then steps back to explain why this experiment matters. He traces his own history with supercharging to the 1950s and early 1960s, when GMC-style blowers taken from two-stroke diesel engines became common in racing. Those blowers were originally scavenging devices used to move air through two-stroke engines so they could start and run, not purpose-built high-efficiency compressors. Over time, racers adapted them because they moved large volumes of air and looked dramatic on top of an engine.
His broader engineering interest has always been air density. When displacement and rpm are otherwise equal, the engine that packs the greatest air density into the cylinders can burn more fuel at the correct air-fuel ratio and make more power. He notes that superchargers can provide excellent throttle response, but they are also parasitic devices that can consume enormous crankshaft power. That is why he has long pursued super-turbo systems, using a supercharger for low-speed response and turbochargers for midrange and top-end airflow. He cites the earlier super-turbo Detroit Diesel 60 Series built for Mike Ryan's Pikes Peak Freightliner as proof of concept: by combining a large screw blower with a turbocharger system and extensive charge cooling, the truck achieved about 200 hp per liter, roughly 2,800 hp from a 14-liter engine, and became the fastest semi ever to run Pikes Peak.
The current project differs because it uses a Roots blower rather than the screw blowers Gale had previously favored. He briefly recounts the historical origin of the Roots design in the mid-1800s, when the Roots brothers developed a rotary machine for moving water and later realized the same mechanism could move air. That led to industrial blowers for blast furnaces and, much later, to the familiar GMC-style superchargers used in racing.
Mechanically, the blower on the Duramax is a 10-71, larger than the vintage 6-71 and 8-71 examples shown for comparison. The rotors are gear-driven so they remain synchronized without touching each other. Air enters through the top, is trapped in the pockets between the lobes and the case, and is carried around the outside of the housing to the outlet. The air does not pass through the center of the rotors. The helical twist in the lobes helps smooth the discharge and reduce shock loading compared with older straight-rotor designs, which produced severe pulsation and belt disturbance.
That operating principle also explains one of Gale's concerns. Because the blower is fundamentally an air mover rather than a true internal compressor, some hot discharge air can leak back through rotor clearances toward the inlet side. If that recirculated air preheats the incoming charge, compressor efficiency deteriorates further. Traditional racing applications often hide this problem because the blower is run wet, with gasoline or methanol introduced upstream. Fuel evaporation cools the charge and masks the blower's true thermal behavior. This test is intentionally dry so the actual compressor performance can be measured without evaporative cooling effects.
The data show that the 10-71 blower reaches a little over 18 psi of boost at 5,000 engine rpm while spinning at 6,000 rpm. On pressure alone, that sounds substantial. However, the corresponding intake manifold temperature reaches 423 degrees Fahrenheit, which is the result that dominates the analysis. Gale compares this with the theoretical heat of compression for a perfect 100 percent efficient compressor at the same pressure ratio. At 18 psi of boost, the natural heat of compression would be about 147 degrees Fahrenheit above ambient.
Instead, the measured temperature rise is about 330 degrees Fahrenheit, which places the blower at only 48 percent compressor efficiency. In other words, everything above the ideal 147-degree rise is treated as compressor inefficiency. The blower is not merely heating the air somewhat more than ideal; it is adding an enormous amount of excess heat. That excess temperature severely reduces the density benefit that the boost pressure would otherwise suggest.
The next set of graphs makes the central point of the episode: boost pressure is not the same thing as useful air density. Ambient air density is given as 69 lb per 1,000 cubic feet. With the 10-71 blower at 5,000 rpm, the boosted air density rises to 97.8 lb per 1,000 cubic feet, a gain of only 29 lb per 1,000 cubic feet. That is roughly a 42 percent increase in density.
The mismatch is striking. The blower produces a 127 percent pressure increase over ambient, yet only a 42 percent density increase. The reason is the extreme temperature rise. Heating the air offsets much of the pressure gain, so the engine does not receive anything close to the oxygen mass that a simple boost number might imply. Gale emphasizes that engines are supercharged to increase oxygen mass per unit volume, not to chase a pressure reading and certainly not to raise intake temperature. In this case, the pressure ratio looks impressive, but the density ratio reveals how much performance is being lost to thermal inefficiency.
To put the result in context, Gale compares the Roots blower with a hypothetical 75 percent efficient turbocharger operating at the same 2.27 pressure ratio. At that efficiency, compressor outlet temperature would fall from 423 degrees Fahrenheit to about 307 degrees Fahrenheit before any intercooling is added. The density ratio would improve from about 1.4 with the blower to about 1.64 with the turbocharger.
He then translates those airflow differences into estimated engine output at 5,000 rpm. The engine displaces 628 cfm at that speed. With the Roots blower, measured airflow is 63 lb/min. Assuming an 18:1 air-fuel ratio and a brake specific fuel consumption of 0.55 lb/hp-hr, the projected output is about 382 hp. Under the same boost pressure with a 75 percent efficient turbocharger, airflow would rise to 73 lb/min. Using the same 18:1 air-fuel ratio but a more favorable 0.40 lb/hp-hr because there is no parasitic blower drive, the projected output becomes 608 hp.
That means only a 16 percent increase in mass airflow produces nearly a 59 percent increase in horsepower. The difference is not just compressor efficiency in isolation; it is also the elimination of the blower's crankshaft power draw. Gale describes the blower's parasitic demand as so severe that it effectively steals horsepower from the engine at a felony level.
The conclusion is not that the project is over, but that the dry Roots blower cannot be left in its current state if the super-turbo concept is going to work. Gale still wants the Roots blower for low-speed throttle response, especially before the turbochargers come fully on line. He also wants to explore the idea of turbocharger boost eventually helping to unload the blower by pushing through it rather than forcing the crankshaft to do all the work.
However, the immediate problem is heat. Continuing to run the BDS 10-71 dry at these temperatures risks damaging the blower and undermines the entire concept through poor air-density performance. The next phase will therefore focus on cooling the system so the blower can survive and the combined super-turbo arrangement can be evaluated properly. The episode ends with that pivot: the first round of testing has revealed the truth about the dry Roots blower's efficiency, and the project now moves toward charge-cooling strategies before the twin turbos are added.