OK,
so you’ve got used to your car now and you crave
more power but we all know that engine tuning is expensive.
Maybe you’ve added a new air filter and exhaust
system which have cost a small fortune but can you feel
the difference? Maybe you can if you’re lucky, but
maybe you’re disappointed. Here’s an idea
that won’t cost you a fortune but could deliver
a greater power increase than the above two items put
together….enter the rolling road...
What is a rolling road dynamometer?
Basically, a rolling road dynamometer is a device that
measures the power output of your car at the wheels. The
rolling road is a set of rollers built into the the floor
that the front wheels (for front wheel drive cars) sit
in and drive. The dynamometer is the equipment that measures
the power and torque the car is putting into the rolling
road. The rollers are connected to a brake and the system
controlling the rollers applies a braking force to the
rollers to resist the force being exerted by the car turning
them. The level of resistance establish the power of the
car. Because the car is not actually moving and the engine
is being pushed hard, large fans will be positioned in
front of the car to provide air to allow the engine to
breathe and for cooling. The car is taken up to peak revs
usually in 3rd gear and (providing it doesn’t blow
up!) the computer connected to the rollers will provide
a graph of torque against revs. Since power is derived
from torque and revs you also have the power curve (at
the wheels).
Is what you see what you get?
It is important to note that this is an accurate reading
of power at the wheels and the figure will always be lower
than the power at the flywheel because of the losses of
power through the clutch, drive shafts, hubs etc. Using
a rolling road, the actual power at the flywheel - the
figure stated by vehicle manufacturers - can only be estimated.
The rolling road operator will tell the computer what
type of car it is and the system will usually have a database
telling it what the typical transmission losses would
be for this car. For example a Peugeot 205 GTI 1.9 may
have an expected figure of 130 bhp at the flywheel and
100 bhp at the wheels, which means there is typically
a 23% loss through the transmission. To measure the power
of the engine at the flywheel it is necessary to remove
the engine and put it on a different type of dynamometer.
In reality, the flywheel figure is irrelevant - it's what's
coming out at the wheels that matters, and that's what
a rolling road dynamometer will give you.
So why bother?
Well, any other kind of tuning is always going to be a
hit and miss affair. Unless the engine is being check
while it is actually running under load there is no way
of knowing what effects adjustments are having. All that
can be done is to make sure things like the timing and
fuel mixture are correct with the engine running light,
normally at low revs. There is no way of telling will
happen when the engine is pushed hard, which can be a
different story altogether. The rolling road provided
a good simulation of the car being driven on the road.
It will indicate flat spots in the torque output etc and
provides a detailed diagnostic graph showing the precise
figures through the rev range enabling an experienced
tuning engineer to assess the results and address any
issues arising. The tuning work carried out can then ensure
optimum performance from the engine that will combine
power with efficiency and hence lower running costs.
If you spend £300 or more on a good exhaust system
and have it installed and a then £50 or more on
a direct air induction kit you could expect a power increase
of 10 bhp or so. However, if your engine is not set up
properly or has a fault, you will certainly not be getting
the best out of your investment. A rolling road diagnosis
and tune could add £50 - £100 to the bill
but is likely to give an additional 10 bhp or maybe more.
As it will almost certainly lead to a significant improvement
in fuel consumption, it has to make economical sense!
Like all high-tech equipment, it's only as good as the
people operating it. The dynamometer only provides the
information, it doesn't tune the engine. Balmuir Garage
are successful tuners of race and rally cars. Their results
speak for themselves. When you put your car on the Balmuir
Garage rolling road you can be confident that we will
be capable of putting the information it provides to good
use.
