Game Development Reference
In-Depth Information
The torque curve for a 2004 Porsche Boxster S is the one shown in Figure 8-2 and is based
on data obtained from the Porsche website at
www.porsche.com
. The peak engine torque value
of 309.2
N-m
occurs when the engine is turning over at 4600
rpm
. The torque curve will be used
a little later on to develop a model that will compute the acceleration of the Boxster S at any
point in time. But first let's discuss another important topic concerning engine performance,
namely engine power.
Power and Torque
Generally, when people talk about the performance of an engine, they refer to its power rather
than its torque. Recall from Chapter 3 that power is an amount of work done in a unit of time.
When applied to the output of a car engine, power,
P
e
, is equal to the engine torque multiplied
by the angular velocity of the engine.
PTw
=
(8.8)
e
e
e
The angular velocity of the engine,
w
e
, in
rad/s
can be obtained by multiplying the engine
turnover rate by 2
p
and dividing by 60.
2
p
Ω
w
=
e
(8.9)
e
60
A plot of the power generated by the Boxster S as a function of engine turnover rate, known
as a
power curve
, is shown in Figure 8-4. Similar to the torque curve, the peak power occurs at
a certain
rpm
level and decreases after that. The peak power output of the Boxster engine is
1.92e + 5
W
and occurs at about 6200
rpm
. Comparing the power and torque curves in Figure 8-2
and 8-4, the peak power for the engine occurs at a higher
rpm
level than does the peak torque.
Figure 8-4.
The power curve for the 2004 Boxster S
