First Air – Then Fuel

Engine modification and tuning for power is basically the same for gas and diesel engines.

Power is force applied across a distance to do work. In an engine, power is torque multiplied by crankshaft revolutions. In other words, to make more power you can increase torque, RPM, or both. Since maximum practical RPM is generally limited by such things as component strength, piston speed, valvetrain dynamics, flame speed, and fuel injection limitations, we’ll direct this discussion toward making more power by increasing torque.

The amount of torque an engine can produce is tied directly to the total amount of heat that can be safety generated in the engine’s cylinders. It is the heat that causes the working fluid (a mixture of nitrogen and exhaust gases) to expand, creating pressure to bear against the pistons, generating torque. It is cylinder pressure that pushes the pistons down, not heat. But it is heat that creates the pressure rise. This is true for both gasoline and diesel engines.

Once we understand the relationship between heat and pressure in an engine’s cylinders, it becomes clear that if we want to make more torque we need to increase the amount of heat released in the cylinder on each power stroke. To do that we need to burn more fuel, or switch to a fuel with a higher heat value. Because Banks deals primarily with street-driven gasoline or diesel engines, we’ll skip going into exotic fuels or fuel mixtures. Instead, we’ll stay with commonly available pump gasoline and pump diesel. Although it has been mentioned several times in other articles on this site, basically all pump gasolines, whether regular or premium, have roughly the same heat content (about 124,800 Btu) per gallon (U.S.). Gasoline blends containing ethanol will have a slightly lower heat value. Similarly, all No.2 diesel has about 138,700 Btu per gallon. Again, blends of No.2 diesel containing some No.1 diesel, biodiesel, or synthetic diesel, will have varying heat values. No. 1 diesel comes in at about 131,800 Btu per gallon (see “About Diesel Fuel” elsewhere on this site).

Okay, what this all comes down to is, how much fuel can we burn in a cylinder on each power stroke? For fuel to burn, or oxidize completely, it needs sufficient oxygen to fully react with the fuel chemically. When fuel and air (oxygen) are mixed together in the correct proportions to fully react, with no fuel or oxygen left over, the mixture is said to be stoichiometric. If there’s too much fuel, not all of it will be burned, and the excess will displace air that could have been used for combustion. If there’s too much air, the full power potential will not be reached, and more fuel could have been consumed for greater heat release. This is the key to more power: increase the quantity of air in the cylinder and you can increase the amount of fuel by a stoichiometrically equivalent amount to make more heat, more power.

When you think about it, nearly every hot rodding trick is geared toward getting more airflow into, and out of, an engine, be it a gas engine or a diesel. These things include a bigger or less restrictive intake path, inducting cooler air, increasing cylinder head flow through porting, bigger valves or different camshaft timing, a less restrictive exhaust system, turbocharging, or supercharging. There are a number of articles addressing these things on this site, such as: “Cool Air Equals Power” and “Airflow – the Secret to Making Power”.

It is only after airflow has been increased that tuning gasoline or diesel engines can occur to maximize power by matching the fuel flow to airflow. At Banks, our systems are designed to first improve overall airflow and then match proper fuel flow through use of the exclusive Banks OttoMind micro-programmer. The OttoMind maximizes power within the safe limits of the engine. There are many systems on the market that attempt to tune for power by simply adding fuel without first increasing airflow. The result is improper air/fuel mixtures, excessive cylinder temperature, and poor fuel economy. Sustained use of such “fuel first” devices will frequently damage engine parts. When you think about it, it is apparent why such an approach is backward: you don’t tune an engine for high output before you modify it.

Are there ever times when an engine is modified beyond the safe limits of the engine? Racing and competition are all about taking things to extreme levels. There is risk involved in “going for it”. Banks recognizes that some enthusiasts are willing to take such risks, especially in pure power contests, such as diesel pickup or diesel truck pull events. For such applications, Banks now offers the Six-Gun and Big Hoss Bundles (see Racing the Diesel elswhere on this site).

Just remember: air first, then fuel. If you follow this basic rule, you’ll be “miles of smiles” ahead of the others.

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