User Guide

108—Dyno2000 Advanced Engine Simulation
the swept distance through which the same force would rotate the torque arm one
full revolution determines the power per revolution: Power Per Revolution = Force or
Weight x Swept Distance. James Watt (1736-1819) established the current value for
one horsepower: 33,000 pound-feet per minute or 550 pound-feet per second. So
horsepower is currently calculated as: Horsepower = Power Per Revolution/33,000,
which is the same as Horsepower = (Torque x 2 x Pi x RPM)/33,000, or simply:
Horsepower = (Torque x RPM)/5,252. The horsepower being calculated by these
equations is just one of several ways to rate engine power output. Various additional
methods for calculating or measuring engine horsepower are commonly used (to
derive friction horsepower, indicated horsepower, etc.), and each technique provides
additional information about the engine under consideration.
Induction Airflow—The airflow rating (a measurement of restriction) of a carburetor
or fuel injection system. Standard automotive four-barrel carburetors are rated by the
measured airflow when the device is subjected to a pressure drop equal to 1.5-
inches of mercury. Two-barrel carburetors are tested at 3.0-inches of mercury.
Intake Centerline Angle—The distance in crank degrees from the point of maxi-
mum intake valve lift (on symmetric cam profiles) to TDC during the valve overlap
period.
Intake Stroke—One of the four 180-degree full “sweeps” of the piston moving in the
cylinder of a four-stroke, internal-combustion engine (originally devised by Nikolaus
Otto in 1876). During the intake stroke, the piston moves from TDC to BDC and
inducts (draws in by lowering the pressure in the cylinder) air/fuel mixture through
the induction system. Note: The 180-degree duration of the intake stroke is com-
monly shorter than the period during which the intake valve is open, sometimes
referred to as the true “Intake Cycle.” The intake stroke is followed by the compres-
sion stroke.
Intake Valve Closing or IVC—Considered the most important cam timing event
from a performance standpoint. The point at which the intake valve returns to its
seat, or closes. This valve timing point usually occurs early in the compression
stroke. Early IVC helps low-end power by retaining air/fuel mixture in the cylinder
and reducing charge reversion at lower engine speeds. Late IVC increases high-
speed performance (at the expense of low speed power) by allow additional charge
to fill the cylinder from the ram-tuning effects of the induction system at higher
engine speeds.
Intake Valve Opening or IVO—The point at which the intake valve lifts off of its
seat, or opens. This valve timing point usually occurs late in the exhaust stroke.
Although IVO does not have a substantial effect on engine performance, it contrib-
utes to valve overlap (the beginning point of overlap) that can have a significant
effect on engine output.
Mini Glossary