Very few subjects can start a flame war on any message board like
the question, which is better horsepower or torque? It seems as
if everyone has opinions on how this question should be answered.
With that in mind I decided to address this topic head on to help
clarify everyone's understanding of this relationship.
To start with we will define power. Power is the expression of
the energy expended over time. In mathematical form it looks like
Power = the change in Energy / the change in time
Which can be manipulated into:
Power = Force x Velocity
And with a little more tweaking we get:
Power = Torque x RPM
Since we'll be referencing horsepower numbers our final equation
looks like this:
Horsepower = (Torque x RPM) / 5252
Since the mathematical aspect is not the main focus of this article
from this point on we will direct our attention to understanding
the relationship between horsepower and torque using the least amount
of math possible.
Torque is a type of force that is applied about an axis or simply
put; it's the measure of twist. Torque is what you feel when you
accelerate and are pushed back into your seat. Furthermore, your
car will accelerate at a rate that exactly matches the torque curve
of the engine barring air and rolling resistance. Torque can be
directly measured by a dyno whereas horsepower cannot. It is extremely
important to understand that horsepower is never measured, it is
a mathematical interpretation of torque over time.
Let's consider this analogy of two different people each turning
a crank that offers 100 pounds of resistance for every one turn.
Person (A) can turn the crank one full revolution in one second
whereas person (B) takes one minute to accomplish the same task.
Both are equally strong (possess the same amount of torque) but
person (A) possesses more power since it took him less time to turn
the crank. Remember that power is defined as torque multiplied by
time. Person (A) could theoretically turn the crank 60 times in
one minute and plugging this into the equation we get:
Equation: Power = Torque x RPM
Person (A) Power = 100 x 60
could produce 6000 "units of power"
Person (B) Power = 100 x 1
would only generate 100 "units of power"
There is a huge difference between these two numbers and this is
where RPM comes into play. As stated above both people possessed
the same amount of torque to turn the crank but one could turn the
crank a lot faster then the other. Using math we were able to find
power output by measuring resistance provided by the crank (100
pounds) and the number of revolutions per minute it could be turned.
Power was never measured in the example above.
Consider the dyno graph below. If we were to look at a hypothetical
engine that produced 50 foot pounds of torque (black line) at any
rpm we would see that horsepower (red) increases at a steady slope.
This liner relationship is due to the formula: Horsepower = (Torque
x RPM) / 5252.
(image courtesy of http://www.hotrodders.com/forum/good-torque-vs-horsepower-article-put-debate-rest-88299.html)
If we modify the torque curve by increasing it at 3000 and 8000rpm
(green peaks shown above) then we would see a respective spike in
the horsepower at the same rpm. What is interesting is that the
horsepower spikes are not the same magnitude at the different rpms.
The spike is greater at 8000rpms because of the torque x RPM part
of the formula. At 3000rpms (a) horsepower increases by approximately
7 but at 8000rpms (b) the horsepower has increased by 19. Below
are the two modified peaks represented mathematically.
Equation: Horsepower = (Torque x RPM) / 5252.
Point (a) Horsepower = (12.5 x 3000) / 5252 = 7.14
Point (b) Horsepower = (12.5 x 8000) / 5252 = 19.04
In both cases the torque values were increased by 12.5 and as you
can see example (a) produced a smaller horsepower increase then
(b) due to the differences in rpms. This suggests that torque elicits
a greater effect on horsepower the further up in the rpm range you
go. This can be attributed to the multiplication factor of rpms.
Does that mean it's better to have torque at higher rpms? It all
depends on what you want to do with your car but don't forget that
gobs of torque at high rpms mean no torque at low rpms. Horsepower
vs. torque is a give and take relationship and you can't have it
How would we apply this to a Saturn or a FWD car for that matter?
Well traction is our biggest limitation and Saturns are light cars
which don't require much torque to get them moving. Besides torque
low in the rpm tends to break parts pretty quickly. Our goal therefore
should not be to produce a lot of torque low in the power band but
to increase torque output further back in the power band. Hondas
are in a similar situation. They lack a lot of bottom end grunt
but come on strong at the top. Using this to their advantage they
build their engines to enhance this trait.
FWD cars are not traditionally quick cars but they can be very
fast cars. If you can increase your power later in the power band
once traction has been established that you can put more of the
power to the ground. This theory is simple to understand but difficult
to implement on a Saturn. We are constantly testing many new ideas
and once we have solutions, TSN members will be the first to know.
forum has become one of the best resources for Saturn performance
on the net. Our members are constantly pushing their cars to new
performance levels. So, log in, share your ideas, and help push
your car’s performance to the next level.
August 2005 TSN will be holding its first ever meet
in Chardon, Ohio. Some of the fastest Saturns in the country will
be attending. Activities will include drag racing, dyno, tech session,
and BBQ. Look for the latest information in the forums.
Jeff and his team Different Racing have big plans
on breaking into some really low quarter mile times this year. Last
year he posted a 12.40 on a pretty healthy nitrous shot. This year
he has a new turbo setup and some serious determination. Visit his
website for the latest news and information. I expect we'll be seeing
some low 12's from him by the end of the year.