Racing Technology with Evan J. Smith
How and Why Internal Combustion Works, Part 2
I n Part 1, I covered the
fundamentals of internal
combustion and dabbled in what it
response and helps move heavy
street vehicles without a big
application of throttle. In contrast,
takes to increase horsepower and short intake runners and long-
torque. In Part 2, I will provide a duration cams will generally make
deeper look into the subject. power higher in the rpm band but at
There is hardly a drag racer who a cost to low-rpm torque and an
doesn’t yearn for more power, harder increase in emissions.
acceleration, and more speed, and Let’s take a hypothetical look at a
depending on what class you run, typical 350 Chevy engine that makes
finding the answer may be a breeze 400 horsepower at about 5,600 rpm.
or quite a challenge. Often, we look Say the engine is equipped with a
to tried-and-true speed secrets, such dual-plane intake and a 600cfm carb
as increasing displacement and with 1 3/4-inch headers. We’ll say it
compression, using aftermarket makes roughly 385 foot-pounds of
heads and cams, or employing a torque at 4,200 rpm.
power adder, such as a blower, turbo, Now, let’s take the same engine
or nitrous oxide. and swap on a 750cfm carb with a
No matter how you slice it, the high-rise, single-plane intake and 1
idea is to burn more fuel and oxygen 7/8-inch headers. Effectively, we
(and to get the most from the air raised the rpm at which the engine
and fuel that enters the engine) Head to any track, and you’ll find a variety of engines in a variety of cars. One example is most efficient, thus changing the
because this will result in a greater is this new Ford Racing Performance Parts Cobra Jet crate engine found in the torque curve. It is likely we’d see an
release of energy, resulting in Aeromotive Super Comp dragster. increase in horsepower, but it would
greater cylinder pressure and occur at a higher rpm. We may even
ultimately a bigger push on the maintain precise control of the on the combination. It’s also see an increase in torque, again at a
pistons; however, picking the best air/fuel mixture to prevent important to note that peak torque higher rpm.
combination of parts is not always so detonation (or an overly rich will occur at the point where the And knowing the results is what a
easy. In seems simple to just go with condition). It’s not as easy as just engine is smart racer is
a big carburetor, intake manifold, stuffing more air into the engine. experiencing after because it
and the best-flowing heads on the And parts selection is even more peak volumetric will help him or
market, but often this leads to a critical when a power adder is used. efficiency. her decide on
mismatch of parts and a less-than- With a blower or turbo, you will see Your intake parts for a
efficient combination. a much greater volume of air being and camshaft specific car.
If you remember in Part 1, I sent to the combustion chambers, so design will Using the second
covered cylinder filling and how it that Stocker cam with an immense have a great combination,
relates to a differential in pressure. amount of duration and valve overlap effect on where we’ll assume the
When we consider the short time might not be a good choice. The in the rpm 350 makes 435
that the valves are open for a given reason is that it will bleed off range peak horsepower at
cycle, we realize how important it is cylinder pressure, which you are horsepower and 6,400 rpm and
to flow the maximum amount of air trying to lock into the cylinders. torque occurs.