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Engine modification and tuning for power is basically the same
for gas and diesel engines.
By C.J. Baker
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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