This engine was pushed to find the limit of a supercharged, intercooled 7.1L Duramax before adding turbos. The key point is simple: pressure by itself does not tell you much. What matters is manifold air density—how much oxygen actually makes it into each cubic foot of intake charge. Here, the blower made positive manifold pressure even at idle, which is why throttle response was so immediate. Then the intercooler cleaned up the compressor’s heat, pulling outlet temperature back down near ambient and turning that pressure into dense air the engine could use. At the 666-horsepower pull, ambient air density contributed 41% of the final manifold air density, while the supercharger and intercooler together contributed 59%. That is why this setup worked so well. The blower gave instant response, the intercooler made the air charge usable, and the engine made 666 horsepower at 18:1 without turbos. Banks iDash made the whole system visible by showing the charge air rating system in real time—ambient, compressor, intercooler, and final manifold density—so you can see what is really making power.
Gale Banks opened the session by correcting the plan from the previous episode. Instead of immediately bolting on twin turbos, he decided to push the 5.0-liter Whipple supercharger as far as possible on the blown, intercooled 427 Duramax. The objective was to find the maximum power available from the blower and intercooler alone, and to evaluate throttle response, which was the main reason for putting the blower on the engine in the first place.
Before the engine was run, Banks outlined the changes since the last test. Intercooler water flow had been increased from 36 gallons per minute to 60 gallons per minute because the team expected to reject substantially more heat. The supercharger drive ratio had also been increased from 50 percent over engine speed to 100 percent over engine speed. Engine speed, previously limited to 3,200 rpm, would now be taken to 5,000 rpm, which meant 10,000 rpm at the blower. That combination was expected to produce significantly more manifold pressure.
Banks also reframed how the test data would be discussed. Rather than casually using the word boost, he emphasized pressure added by the blower, pressure lost through the intercooler, and the final manifold absolute pressure in the intake manifold. In his view, the more meaningful metric was manifold air density, because supercharging and intercooling are ultimately about packing more oxygen into each cubic foot entering the cylinders.
That distinction shaped the entire test. Pressure alone was not the point; the real target was dense air at the manifold. A good cold-air intake, the supercharger, and the intercooler all contribute to that result. Banks repeatedly tied manifold air density directly to horsepower and torque, arguing that, all else being equal, the engine with the highest manifold air density wins.
Once the engine was running, one of the first observations was that the system produced positive manifold pressure above ambient even at idle. At 1,000 rpm, the blower and intercooler were generating about 6.5 psi above ambient. Banks noted that this was far beyond what a pair of turbos would normally provide at idle.
Throttle response was the next focus. Several quick throttle stabs showed the engine accelerating almost like a naturally aspirated free-revving engine, quickly running into the rev limiter at roughly 5,300 rpm. Banks described the response as unlike any turbocharged diesel he had seen. He wanted to quantify rpm gain per second from the logged data and compare it with a blown gasoline engine, but even without that analysis, the immediate response was obvious.
The idle air-density numbers reinforced the point. Ambient air density at the time was about 72.7 pounds per 1,000 cubic feet. The blower and intercooler added another 30 pounds per 1,000 cubic feet at idle, bringing manifold air density to roughly 103 pounds per 1,000 cubic feet. That represented about a 40 percent increase in air density at idle, which Banks considered remarkable.
With the engine loaded at roughly 100 horsepower and around 2,400 to 2,500 rpm, Banks introduced what he called CARS, the Charge Air Rating System. The display breaks manifold air density into contributions from ambient conditions, the compressor, the intercooler, and the final intake manifold result. He explained that the same information could be shown across multiple iDash screens or cycled through on a single gauge, and that the data becomes available when using an AirMouse sensor package.
The first gauge represented ambient contribution. The second separated the compressor contribution from the intercooler contribution. The third combined those two into what Banks called boost air density, meaning the total density increase produced by the boost-air system. The fourth displayed manifold air density, which he treated as the key performance metric because it correlates directly with torque and horsepower. This framework set up the full-power pull by showing not just how much pressure the system made, but how effectively it converted that pressure into dense, cool intake charge.
The team then made a full-power run to 5,000 rpm at an 18:1 air-fuel ratio. During the pull, the dyno showed a peak of 666 horsepower. Banks reacted to the number with some surprise, but clearly regarded it as serious output for a blower-only diesel combination.
He was especially impressed that the system was producing nearly 30 pounds of boost-air density at idle, and he contrasted the setup with monster-truck engines. Those 540-cubic-inch blown alcohol Chevrolet engines typically idle well above 1,000 rpm and use very loose torque converters, so they are not heavily loaded until 4,000 to 4,500 rpm. By comparison, this diesel was already showing strong charge-air performance and immediate response at low speed.
The team then attempted to extend the test to 5,500 rpm at the same 18:1 air-fuel ratio. The engine was still making north of 600 horsepower there, but Banks concluded they were already past the horsepower peak seen at 5,000 rpm. The engine pulled cleanly through roughly the 2,500 to 5,500 or 5,600 rpm range without missing a beat, which helped define the useful operating window of the combination.
As the team explored higher engine speed, attention turned to a likely fuel-system limitation rather than an airflow problem. Banks and the crew suspected the stock CP3 pumps did not like the speed they were being forced to run. The engine was using two stock CP3.3 pumps, described as standard out-of-the-box replacement pumps.
Because the pumps were being driven in an 80 percent engine-speed relationship, running the engine to 5,500 rpm meant the pumps were still turning about 20 percent slower than engine speed, yet that was already well beyond the maximum speed those pumps were intended to tolerate. Banks concluded that they had probably not found the airflow limit of the blower-and-intercooler system at all; instead, they were running into the practical speed limit of the fuel pumps. His answer was straightforward: the combination would need S&S pumps for the next step.
Before shutting down, Banks still wanted one more transient test. He asked for the engine to be stabilized around 1,500 rpm and then hit with a wide-open-throttle slam, with the operator instructed to pull out once engine speed reached about 4,500 to 5,000 rpm. The purpose was not to make another power number, but to capture rpm change per second and compare response across future modifications.
The resulting acceleration confirmed the earlier impression. Banks declared that the engine had real throttle response, comparing it favorably against a 540-inch blown alcohol Chevrolet and emphasizing that this was still a diesel. For him, the blower had accomplished exactly what it was intended to do: provide immediate engine acceleration and strong low-speed charge-air support that a turbo-only setup would struggle to match.
After the run, Banks reviewed a screenshot taken at the 666-horsepower point using the CARS layout. Ambient air density was 72.5 pounds per 1,000 cubic feet, contributing 41 percent of the final manifold air density. The Whipple compressor added 50.7 pounds per 1,000 cubic feet, accounting for about 29 percent. The intercooler added 53.5 pounds per 1,000 cubic feet, slightly outperforming the blower itself and contributing about 30 percent.
Combined, the compressor and intercooler produced 104.3 pounds per 1,000 cubic feet of boost air density, which represented 59 percent of the final manifold air density. Added to the ambient contribution, that yielded a final manifold air density of 176.8 pounds per 1,000 cubic feet. Banks noted that humidity was included in the calculation through the AirMouse ambient sensor, although from that point forward he focused mainly on temperature, pressure, and density.
The pressure breakdown started with ambient pressure at 14.45 psia. The compressor added 21.61 pounds, bringing pressure to 36.06 psia. The intercooler then imposed only a small restriction, dropping a little over half a pound, for a final manifold pressure of 35.52 psia. On the temperature side, ambient was 73.4 degrees F. The compressor raised temperature by 248 degrees, producing 322 degrees F at the compressor outlet. The intercooler then removed 245 degrees, bringing final manifold temperature down to 77.2 degrees F, only 3.8 degrees above ambient.
Banks used those numbers to argue that the system was highly efficient. The intercooler effectively cleaned up the heat added by the supercharger, nearly returning charge temperature to ambient. He stressed that a properly designed intercooler can completely transform the usefulness of a supercharger by recovering density that would otherwise be lost to heat.
Banks summarized the result by saying that 666 horsepower is a strong number for a street-driven diesel and may even be a record for a blown 7.0-liter diesel, though he did not claim certainty on that point. Even so, it was not the final target. This was a monster-truck project, and he wanted roughly twice that output, something in the 1,300-horsepower range.
That led directly to the next phase of the build. The upcoming configuration would add two Precision turbos and a custom intercooler feeding into the Whipple, then through its intercooler, and finally into the 7.0-liter Duramax. In other words, the blower-only test established the baseline and demonstrated exceptional throttle response, but the larger engineering story was only beginning. The next step would be a compounded system designed to push the engine far beyond what the supercharger and intercooler could achieve on their own.