Fuel flow is the measurement that drives engine development. Brake specific fuel consumption tells you how much fuel mass it takes to make horsepower, and that number affects tuning, airflow, boost, timing, and overall engine efficiency. The problem is that diesel systems return fuel to the tank, so supply flow alone does not tell you what the engine actually used. On top of that, older fuel flow setups have enough lag and hysteresis that they only work once everything stabilizes at fixed throttle. This Coriolis setup fixes the measurement problem. It responds quickly, measures mass flow directly, and does it with low pressure drop. By using one meter on supply and one on return, we can calculate true net fuel consumption in real time instead of waiting for the system to settle. That means we can track brake specific fuel consumption through throttle transients, not just at steady state. When a change improves the number, the engine got better. When it hurts the number, it didn’t.
Gale Banks opens by framing fuel-flow measurement as one of the most important tools in engine development. Whether the work involves tuning, supercharging, turbocharging, exhaust systems, or cylinder-head development, he says it ultimately comes back to brake specific fuel consumption, or BSFC. In his explanation, "brake" refers to the dyno, and fuel consumption refers to the mass of fuel required to produce one horsepower for one hour.
Banks uses simple rule-of-thumb BSFC values for estimating system requirements. For diesel, he uses about 0.42 pounds of fuel per horsepower-hour. For gasoline, he uses 0.500, or half a pound per horsepower-hour. He emphasizes that these are estimating values, but they are central to determining fuel flow, air-fuel ratio, turbocharger or supercharger sizing, and intercooler requirements. In his view, BSFC is the key metric that ties together nearly every major engine-development decision.
Banks explains that BSFC is highly sensitive to mixture quality and overall engine efficiency. If the mixture is too rich, efficiency suffers and the BSFC number rises. If it is too lean, that is also undesirable; despite the common assumption that leaning an engine out always improves efficiency, he notes that the goal is to get as close as possible to a mixture that consumes all the fuel in the cylinder effectively.
He also points out that engine efficiency depends on more than fuel quantity alone. Timing, peak cylinder pressure location, exhaust pressure relative to intake manifold pressure, and what he calls the pressure differential across the engine all affect the result. Those factors may be discussed in more detail later, but his central point is that fuel flow is the "holy grail" because BSFC reveals whether a change actually improved the engine or made it worse.
A major limitation in conventional fuel-flow measurement is transient operation. On a boat, Banks notes, the throttle is often set and left in one position for long periods. On land, however, vehicles are constantly accelerating, braking, maneuvering, and changing load. Those changing conditions are transients, and they are exactly where accurate real-time fuel-flow data becomes difficult.
Banks says that up to now, the available fuel-flow measuring equipment has not been able to track either quick transients or even gradual ones with the fidelity he wants. That matters in stop-and-go driving, road racing, and any other use case where throttle position and engine load are changing frequently. His goal is to measure BSFC accurately during those transient events rather than only at stabilized steady-state conditions.
The featured hardware is an approximately $8,000 Coriolis fuel-flow meter, and Banks notes immediately that one meter is not enough for the intended diesel application. Because the system must measure both fuel supplied to the injection system and fuel returned from it, the setup requires two meters.
The unit shown is made by Endress+Hauser, a company Banks describes as a supplier of many kinds of instrumentation and flow meters. He selected the Coriolis type because it is highly responsive, very accurate, and introduces relatively little pressure drop between inlet and outlet. This particular meter is calibrated for diesel, but he notes that it can be calibrated for many other fluids as well. He even remarks that it could measure water or honey. Beyond simple volumetric flow, the meter can also determine density and viscosity, making it much more capable than a basic gallons-per-minute or gallons-per-hour device.
Banks chose the half-inch version to combine low pressure drop with high flow capability. According to his figures, it can flow 400 gallons per hour with a nominal pressure drop of about 2 psi.
Banks then explains the Coriolis measuring principle, crediting the concept to the French mathematician and physicist Gaspard-Gustave de Coriolis, born in 1792. Inside the meter is a tube that is kept in constant oscillation by an exciter. When no fluid is flowing, the tube oscillates uniformly. Sensors at the inlet and outlet register that motion.
Once fluid begins moving through the tube, the inertia of the moving fluid causes the tube to twist. Due to the Coriolis effect, the inlet and outlet sections of the tube oscillate differently at the same time. The sensors detect the resulting difference in oscillation in time and space, known as phase shift. That phase shift is proportional to the amount of liquid flowing through the tube. As flow velocity increases, the deflection of the oscillating tube increases as well. Banks also notes that the same calculations can be used to determine fluid density at the same time.
He briefly digresses into Coriolis's broader scientific work, including his analysis of billiard-ball motion, but the engineering takeaway is straightforward: this measuring method is not new, and it offers the responsiveness and precision Banks wants for advanced engine-development work.
Banks uses the meter's rated capacity to illustrate its suitability for very high-power applications. At 400 gallons per hour, and with diesel weighing roughly 7 pounds per gallon, the meter could pass about 2,800 pounds of fuel per hour. Using his diesel BSFC rule of thumb of 0.420 pounds per horsepower-hour, that amount of fuel corresponds to about 6,667 horsepower.
He notes that engine developers often refer to the BSFC value as "420," dropping the decimal while still meaning 0.420. On paper, the meter's capacity appears sufficient for nearly 7,000 horsepower. However, he immediately points out an important diesel-system complication: not all supplied fuel is actually burned. Diesel systems return a significant portion of fuel back to the tank because the fuel is also used to cool the injection pump and the injectors.
If 30 percent of the supplied fuel is returned, or even if half of it is returned, the net fuel consumed by the engine is much lower than the gross supply flow. Even in the extreme example of 50 percent return, Banks says the setup would still support about 3,333 horsepower of actual fuel consumption. That is why the complete measurement system uses two half-inch flow meters, one on supply and one on return, with the data fed into one of Banks' data-acquisition systems to calculate net fuel usage and then real-time BSFC.
To show what the new Coriolis setup is replacing, Banks presents the company's older in-house fuel-flow measurement system, which weighs 16 pounds. Banks says they have built and used these systems for years in dyno cells and in field testing. He recalls using one on a trucking-company project aimed at reducing fuel expense. By instrumenting a truck and analyzing fuel consumption on the dyno and on the road, they developed the precursor to the PedalMonster.
In that fleet application, the goal was not sharper throttle response, but the opposite. Banks says they deliberately gave the throttle a softer, more spongy response so drivers would use less fuel. In a fleet with hundreds of trucks, even very small reductions in fuel use matter.
He then walks through the old system's fuel path. Fuel enters, is filtered, passes through a gear pump, is filtered again more finely, then goes to a vapor separator and regulator. The regulator holds output pressure at about 15 psi, which he says is near optimum for the Bosch pumps they were using. He contrasts that with Denso systems such as those on the L5P Duramax, which may run at 80 to 90 psi; this older setup would not work with a Denso pump. After vapor separation, fuel enters three float chambers. Fuel is delivered from those chambers to the engine, while returned fuel from the engine also comes back into the system and reenters the float chambers. The result is effectively a closed loop in which the incoming fuel from the external supply is only the makeup fuel actually being consumed to make horsepower.
Banks defines the key measurement terms clearly. Gross fuel flow is the fuel sent out to the engine. Return fuel flow is the fuel coming back from the engine. Net fuel flow is the difference between the two, and that net value is the fuel actually being burned to produce power.
The weakness of the older float-chamber-based system is lag, or hysteresis. It takes time for the system to stabilize after a change in throttle or load. Because of that, it is only suitable for fixed-throttle, fixed-power testing. In practice, Banks says they would wait for temperatures and flows to stabilize, hold the condition for a few seconds, and only then begin recording data. Any throttle change required another waiting period before useful readings could be taken.
That makes the old system unsuitable for transient testing. By contrast, Banks expects the Coriolis meters to provide almost instantaneous fuel-flow data. He sees that as a major advance in tuning accuracy and in the development of complete engine systems, including airflow, combustion behavior, and even fundamental geometry choices such as bore, stroke, and rod ratio. His conclusion is that BSFC remains the ultimate measurement: every engineering change can be judged by whether that number improves or worsens. If BSFC gets better, the change helped. If it gets worse, it did not.