This small-block Chevy didn’t just make modest power because it’s old. It gave away power in the intake tract. At wide-open throttle, ambient air density was 72.87 pounds per thousand cubic feet, but only 62.05 made it to the intake manifold. That loss came from pressure drop and, even more, heat soak: ambient air was 72.6 degrees, while manifold air climbed to 131 degrees. On the dyno, that worked out to 169.6 rear-wheel horsepower, with roughly 30 horsepower missing between the grille and the manifold. That’s the real problem with an exposed element air cleaner under the hood. It ingests hot air that has already been through the radiator area, and hot air carries less oxygen mass per cubic foot. Less air mass means less fuel can be burned, and that means less power. Using Banks iDash data logging, we could see the density loss directly instead of guessing. The takeaway is simple: if you want the engine to make the power it should, you need to protect air density with cooler, less restricted inlet air.
This episode centers on a dyno test of the shop's rough 1966 Chevrolet C20 project truck. Before it ever reached the rollers, the truck immediately reminded everyone what kind of vehicle they were dealing with. On startup, it leaked heavily and sprayed a significant amount of fuel into the engine bay and onto the firewall. The smell of raw fuel was obvious, and the engine made enough strange noises that the crew initially struggled to tell whether it had actually started or whether the starter was still just grinding away. After stopping the attempt, they repaired the fuel line and continued patching the truck together well enough for a test pull.
The truck was described as being held together with temporary fixes. Wiring repairs were made quickly, and the crew openly admitted that on a better vehicle they would have sealed electrical connections properly with shrink wrap or even soldered them. This truck, however, was treated as a barely serviceable test subject rather than a restoration candidate. Even so, they got it running, instrumented, and ready for the dyno.
The truck itself is a 1966 C20, an eight-lug heavy-duty Chevrolet pickup that the team jokingly referred to as their one-dollar truck. Gale Banks gave it a visual inspection and immediately pointed out its many improvised and worn-out features. The front carried a crude grille-blocking panel that could theoretically alter airflow or help warm the engine in winter, much like old farm-truck practices. Underhood condition was poor, with obvious grime, makeshift fixes, and signs of age everywhere.
The truck also carried a 32-year-old Corvair turbo muffler, which Gale recognized by sound and appearance. The cowl area had been modified in a way that suggested someone had interfered with the original ventilation arrangement. The engine bay looked neglected enough that even an air freshener had apparently been placed there to mask odors. Gale's overall reaction was that the truck represented many of the bad hot-rodding habits of earlier decades, and he made it clear that one dollar may still have been too much to pay for it.
Despite the truck's condition, the dyno setup was fairly comprehensive. The team had wheel horsepower measurement, water temperature, air-fuel ratio, manifold air density, manifold air temperature, exhaust gas temperature, RPM, and manifold absolute pressure all being logged. An O2 sensor had been installed in the exhaust, and a thermocouple was also in place. Ambient air density was being tracked as well, using an air sensor mounted in the nose of the truck.
That instrumentation mattered because the goal was not just to record peak horsepower, but to understand why the engine made whatever power it made. Gale immediately focused on the intake system and the quality of the air reaching the engine. He noted that the truck used an open-element air cleaner located under the hood, where it would ingest heated air that had already passed through the air-conditioning condenser and radiator. In his view, that setup severely reduced intake-air density and therefore horsepower. He contrasted it with enclosed cowl-induction arrangements, including early NASCAR-style systems that drew cooler, higher-pressure air from the base of the windshield.
The engine in the truck was a GM Goodwrench 350 crate engine installed in 1999 for a little over $1,700. It was paired with an Edelbrock C4B intake manifold and a Carter AFB carburetor. The truck also wore orange plug wires and a non-original air-cleaner assembly. Based on the way the engine idled, the crew initially wondered whether it had a camshaft, but Gale dismissed that idea. He explained that these crate engines typically used very mild camshafts, roughly in the 190- to 200-degree range at 0.050-inch tappet lift, making them stump-pulling truck cams rather than high-RPM performance grinds.
Gale expected the engine to be effectively finished by about 4,200 to 4,400 RPM, though he allowed that the actual horsepower peak might drift somewhat depending on the transmission and shift schedule. He predicted a torque peak around 1,800 RPM, emphasizing that this was fundamentally a truck engine. He also put the combination in historical context. A 1966 Chevrolet truck like this might originally have come with a 283 or a 327, in two-barrel or four-barrel form, with factory horsepower figures generally somewhere below or slightly above 200 horsepower. By modern standards, those engines were not especially strong.
The dyno session came with several concerns beyond engine output. The truck was still leaking fluids, and the crew worried about fuel, oil, or coolant ending up on the dyno. The tires were believed to be 19 years old, which did not inspire confidence at speed. The rear brakes did not work at all, leaving only the front brakes and the parking brake to slow the truck during coastdown. Even the exhaust routing drew attention because parts of it hung unusually low under the chassis.
Because of the truck's condition, the mood around the dyno pull was cautious. Gale made it clear that he preferred not to be anywhere near the vehicle during the run. Still, with enough steel around the operator and the truck strapped down, they proceeded. The expectation was not that the truck would produce impressive numbers, but that the data would reveal where the power was being lost.
The pull was made in third gear, beginning at 27 mph and ending at 95 mph over a 15-second sweep. The truck survived the run, and the data showed a maximum uncorrected wheel horsepower of 169.6, which the team rounded to 170 rear-wheel horsepower. Peak horsepower occurred at 4,738 RPM. Maximum observed torque was 215.7 lb-ft at 3,422 RPM, with the torque peak occurring at 60.6 mph and the horsepower peak at 87 mph.
Those numbers settled the crew's informal betting pool. One estimate had been 190 rear-wheel horsepower, another 198, and another 175. The 175-horsepower prediction came closest and won. More important than the bet, however, was what the shape of the curve suggested. Gale noted that a stock intake manifold and stock carburetor would likely have produced a horsepower peak earlier, around 4,200 to 4,400 RPM. The Edelbrock C4B manifold, based on his past experience, tended to trade away some torque while adding a little horsepower at higher RPM. That matched what they saw: the engine's power peak had moved upward, but the overall result was still unimpressive.
After the dyno run, Gale shifted from raw output to the underlying airflow math. Using the logged data from the Data Monster and reviewing it through DataLogViewer.com, he explained that engines burn air and fuel by mass, not by volume. At full power, this engine was running at about a 12.5:1 air-fuel ratio, meaning 12.5 pounds of air were being mixed with 1 pound of fuel. Because the engine processes air in cubic feet per minute, the critical question becomes how much air mass exists in each cubic foot entering the engine. That is why Gale focuses on air density, measured here in pounds per thousand cubic feet.
Ambient air density during the test was 72.87 pounds per thousand cubic feet. At wide-open throttle, the intake manifold air density was only 62.05 pounds per thousand cubic feet. That meant the engine was missing 10.82 pounds per thousand cubic feet compared with ambient, a loss of roughly 15 percent before the air even reached the cylinders. Since the engine made 170 horsepower at 62.05 pounds per thousand cubic feet, Gale divided 170 by 62.05 and calculated 2.74 horsepower per pound of air density. Multiplying that by the ambient density of 72.87 yielded 199.6 horsepower, which he rounded to 200 horsepower. In other words, about 30 horsepower had been lost simply because the intake system failed to deliver ambient-density air to the manifold.
Gale then broke down the causes of the density loss. Air density is driven by temperature, pressure, and humidity. Humidity during the test stayed essentially constant at a little over 40 percent, so it was not the main factor. Ambient pressure was 14.53 PSI absolute, while manifold pressure at wide-open throttle was 13.73 PSI absolute. That pressure drop mattered, but the temperature rise was far more dramatic.
Ambient air temperature was 72.6 degrees, while intake-manifold air temperature reached 131 degrees. That was an increase of 80.4 percent. To Gale, this was definitive proof that the truck had a true hot-air intake. The open-element air cleaner was sitting underhood, drawing air that had already been heated by the radiator and surrounding engine-bay environment. Coolant temperature was 180 degrees, so the incoming air was being exposed to substantial heat before combustion. His conclusion was blunt: an exposed underhood air cleaner may look like a performance part, but in this case it was plainly costing power. The dyno data showed exactly how much.
The final takeaway from the dyno session was that 170 rear-wheel horsepower was not an impressive result for this C20, but the test successfully identified one major reason why. The truck clearly needed more power, and the data showed that intake-air management alone represented a meaningful opportunity. Gale used the session as a practical lesson in why air density matters and how poor intake design can leave substantial horsepower on the table.
The episode closed by setting up the next phase of the project. The team hinted that they had involved Gale's iDash and brought in Jeffrey Transue, described as a conceptual artist, to develop ideas for what comes next. The next episode would reveal the concept art and additional surprises, building on the dyno baseline established here.