Boost pressure by itself does not tell you how much oxygen the engine is getting. Heat matters. In this supercharged 7.0L Duramax test, adding a liquid-coupled intercooler cut manifold temperature by 200 degrees, reduced boost, and still raised manifold air density 14%. That denser charge let the engine make more power while taking load off the blower, which is why horsepower went up even before adding fuel. At the same fuel rate, output increased from 235 to 252 horsepower. With the air-fuel ratio matched, it climbed to 278 horsepower. Exhaust temperature and heat rejected to the cooling system also dropped. That is the real job of an intercooler: improve air density, control temperature, and do it with very little pressure loss so the engine keeps pulling under sustained load instead of derating.
In this episode of the monster truck engine build, Gale Banks focuses on a single change to a supercharged 7.0-liter Duramax: adding an intercooler. The engine had previously been tested with a 5.0-liter Whipple supercharger, and that blower had already produced strong results on the GMC 1071 combination shown in the earlier episode. For this round of testing, the Whipple supercharger remained part of the system, but the team added what Banks calls the new air-density machine: a Whipple liquid-coupled intercooler.
Unlike the air-to-air intercoolers commonly used on cars and trucks, this unit uses water flowing through the core inside the intake manifold to absorb heat from the compressed air. That heated water is then routed to a large low-temperature radiator, where the heat is rejected before the water returns through the system. Banks compares the concept to the Ford 6.7-liter diesel arrangement, but says this version is substantially larger and more capable.
Because the intercooler core carries water inside the intake manifold, Banks' team pressure-tested the installed core with air before running the engine. The goal was to verify that no water could leak into the cylinders, since water does not compress and could cause catastrophic damage. The core passed the test by holding 25 PSI for 30 minutes with no loss.
Coolant circulation for the intercooler system is handled by a pair of billet aluminum Stewart EMP pumps. Depending on the head pressure requirement, the pumps can be configured in parallel for greater volume or in series for greater pressure. Banks notes that he has used Stewart EMP pumps for more than 15 years and favors their straight-through design. For this test series, the system was run at 36 gallons per minute, with a target water temperature rise through the core of about 20 degrees Fahrenheit at full power. He also places the setup in historical context, noting that Banks first used liquid-coupled intercooling on offshore racing engines in 1975 and later on Roy Woods' M/Sub Monza in 1976.
Banks frames the entire test around a simple claim: adding only intercooling can increase horsepower or improve fuel economy without changing blower speed or adding fuel. For the first comparison, nothing else in the combination was altered. The engine was tested at 3,200 RPM with the blower running at 50 percent overdrive, or 4,800 RPM. In the non-intercooled baseline configuration, the engine produced 235 horsepower at a 23.2:1 air-fuel ratio and 14 pounds of boost. Banks says this operating point was chosen to represent the kind of sustained output required when pulling a serious load up a 6 percent grade.
He argues that intercoolers should not be judged by flow-bench numbers or short dyno sweeps alone. In his view, the real standard is sustained full-load testing with the ability to measure both heat rejection and pressure loss. On spark-ignited engines, a more efficient intercooler allows more power before detonation becomes the limit. On diesels, it allows more power before exhaust gas temperature or coolant temperature becomes the limiting factor. Under towing or cruising conditions, it can also improve fuel economy. Banks emphasizes that many stock and aftermarket intercoolers may look acceptable in brief tests, yet fail to reject heat fast enough during long pulls, leading to rising EGT, rising coolant temperature, and eventual power derates as the engine removes fuel to protect itself.
A major theme of the episode is that boost pressure alone does not describe how much useful air mass is entering the engine. Banks explains manifold air density as the number of pounds of air mass contained in every thousand cubic feet displaced by the cylinders. That air mass, not boost pressure by itself, determines how much fuel can be burned efficiently and therefore how much power can be produced.
To illustrate the point, he demonstrates a sealed one-cubic-foot container of air heated on a hot plate to simulate a compressor adding heat and boost. In the heated state, the air density inside the box is 73.2 pounds per thousand cubic feet, the temperature is 188 degrees Fahrenheit, and the gauge pressure is 3.3 PSI. When the air is cooled, the pressure drops to zero and the temperature falls to 67 degrees Fahrenheit, yet the air density remains exactly 73.2 pounds per thousand cubic feet. The lesson is that boost can rise simply because temperature rises, without any gain in air density. In that case, the boost gauge is misleading. A highly efficient intercooler allows the same mass of air to occupy the same volume at lower pressure by removing heat, which is why Banks argues that air density is the meaningful metric rather than boost alone.
As part of the series, Banks introduces a new intercooler rating system called Banks IRS, tied to patent filings covering charge-air monitoring and charge-air control dated February 8, 2019. He says these readings will be included in iDash SuperGauge and iDash DataMonster instruments. The purpose of the system is to quantify intercooler performance in terms that matter on the vehicle, not just on a bench.
Banks separates intercooler performance into effectiveness and efficiency. Effectiveness describes how well the intercooler reduces charge-air temperature relative to the cooling medium. Efficiency includes both heat rejection and the pressure loss required to force the air through the core. He also stresses that a proper intercooler must not choke airflow to the engine radiator. Using examples from Banks Ram-Air intercoolers for 5.9-liter and early and late 6.7-liter Cummins applications, he explains that simply making a core thicker can create cooling-system problems if fin density and airflow-through performance are not managed correctly. According to Banks, a good intercooler must minimize pressure drop between the turbocharger and intake manifold, maximize cooling, and preserve enough airflow on the cold side so the radiator can still do its job.
The comparison between the previous non-intercooled test and the new intercooled runs produced what Banks describes as shocking results. In the baseline test without the intercooler, the Whipple produced 14 pounds of boost and the intake manifold temperature reached 279 degrees Fahrenheit. With the intercooler installed, boost dropped to 8.9 pounds, a 35 percent reduction, while intake manifold temperature fell to 79 degrees Fahrenheit, a 72 percent reduction.
Despite the lower boost, manifold air density increased from 102.5 to 117.1 pounds per thousand cubic feet, a 14 percent gain. Mass airflow also increased from 37.5 to 39.3 pounds per minute, up 4.8 percent. Banks explains that by cooling and densifying the air under the blower, the intercooler effectively unloads the supercharger. The blower operates at a lower pressure ratio, adds less heat, and slightly improves mass flow. In his words, it is almost as if the blower thinks the engine is bigger.
With no additional fuel added, the air-fuel ratio leaned from 23:1 to 25:1 because of the increased airflow. Horsepower rose from 235 to 252, a 7.4 percent gain or 17 horsepower on the same fuel. Banks attributes that increase primarily to reduced parasitic horsepower consumed by the blower. He then ran a third comparison with the same 23:1 air-fuel ratio as the baseline. In that case, horsepower increased from 235 to 278, a gain of 43 horsepower or 18.3 percent. Of that increase, 17 horsepower came from reduced parasitic loss, leaving a net gain of 26 horsepower, or 11.1 percent, attributable to the additional air mass. He notes that this closely tracks the 14 percent increase in manifold air density.
Banks then breaks down the manifold air density into its contributing sources. In the baseline test, ambient air density was 69.6 pounds per thousand cubic feet, boost air density contributed 32.9 pounds per thousand, and manifold air density totaled 102.5 pounds per thousand cubic feet. In the intercooled tests, ambient air density was 69.3 pounds per thousand. The supercharger outlet was now only 9.1 PSI at 230 degrees Fahrenheit, contributing 23.1 pounds per thousand cubic feet. The intercooler then added another 24.7 pounds per thousand cubic feet while dropping pressure only 0.2 PSI, from 9.1 to 8.9 PSI, and reducing temperature to 79 degrees Fahrenheit. Combined boost-system air density therefore rose to 47.8 pounds per thousand cubic feet, producing a final manifold air density of 117.1 pounds per thousand.
Expressed as percentages of total manifold air density, ambient conditions accounted for 59 percent, the supercharger contributed 20 percent, and the intercooler contributed 21 percent. Banks highlights the surprising conclusion that in this configuration the intercooler contributed slightly more air density than the supercharger itself. Overall, the boosting system's density contribution increased 45 percent, from 32.9 to 47.8 pounds per thousand cubic feet, even though boost pressure was reduced by 36 percent.
The thermal results reinforced the air-density data. Intake manifold temperature dropped by 200 degrees Fahrenheit from test one to test two. Exhaust gas temperature fell from 1,042 degrees Fahrenheit to 903 degrees Fahrenheit, even while the engine was making more power. Banks says this is expected because cooler intake air generally leads to lower exhaust temperature, but he also points to another benefit: reduced heat rejection into the engine coolant. Heat rejected to the coolant dropped from 1,090 BTU per 100 horsepower to 990 BTU per 100 horsepower, nearly a 10 percent reduction.
The intercooler itself showed strong performance. At 39.3 pounds per minute of airflow and 36 gallons per minute of water flow, the cooling water gained 22 degrees Fahrenheit through the intercooler, very close to Banks' 20-degree target. Pressure drop through the intercooler was only 0.2 PSI. Charge-air temperature dropped 151 degrees through the core. Using the new Banks IRS metrics, intercooler effectiveness at this power level was 95.5 percent, and intercooler efficiency was 90.6 percent. Banks says the unit still has substantial overhead left for the later stages of the monster truck project.
Although fuel economy is not usually the headline topic for a monster truck engine, Banks deliberately ran these tests in the 250-horsepower range because that is where truck owners would care about efficiency under load. In the baseline 235-horsepower configuration, fuel consumption was 97.9 pounds per hour, which works out to 41.7 pounds of fuel per 100 horsepower per hour. In test two, with the intercooler added but no extra fuel, fuel flow remained 97.9 pounds per hour while output rose to 252 horsepower. That reduced fuel consumption to 38.8 pounds per 100 horsepower per hour, a 7 percent improvement in fuel economy.
In test three, fuel was added to restore the original 23:1 air-fuel ratio, bringing fuel flow to 109.7 pounds per hour at 278 horsepower. Even then, fuel consumption was only 39.4 pounds per 100 horsepower per hour, still 5.6 percent better than baseline. Banks' conclusion is that a highly effective, highly efficient intercooler can reduce parasitic load, increase horsepower with no additional fuel, support larger gains when fuel is added to match air-fuel ratio, lower intake and exhaust temperatures, reduce heat rejected to the coolant, and improve fuel economy at the same time. He closes by previewing the next stage of the build: adding two Precision turbos along with two wastegates and a blow-off valve from Turbosmart.