Rolling Road DayGood morning and welcome to everyone from 'Cruisewirral'.
My name is Dave Jones and I look after the Research & Development. department
here at PECO. As such I'll be the one who's going to put your car through its paces
on our rolling road today, promise to treat it gently!
I'm sure a lot of you have been to a rolling road before, but for those of you who
haven't, I've made a few notes to help you understand what it's all about.
What is a Dynamometer?A dynamometer is a tool used to measure power and torque produced by an engine.
There are basically two types of dyno, an engine dyno and a chassis dyno (rolling
road).
Engine Dyno:With an engine dynamometer the engine is attached directly to the dyno, the power
and torque produced are measured at the flywheel of the engine, hence the term
'flywheel power'. This type of dyno is mainly used by manufacturers and engine
builders for testing purposes.
If you want to see what it looks like, just ask, we've got one of these here at PECO as
well.
Chassis Dyno:With a chassis dynamometer the power and torque produced by the engine can be
measured with the engine still in the vehicle. The main difference being that the
power is measured at the drive wheels and not the flywheel. Because of this the
results produced are always less than the results produced from an engine dyno. This
is due to the power lost through the transmission and tyres.
Most rolling roads these days will calculate flywheel power by measuring the drag on
the overrun, as will ours, however these figures are not, and can never be, truly
accurate.
Because of this I will not bother doing this test.
What really matters is how much power you get at the drive wheels, if you want to know your true flywheel
power then take the engine out and put it on an engine dyno.
How does a Rolling Road work?There are two basic types of rolling road.
Steady State (Brake) Dyno :The cars wheels drive a drum that has a brake, attached to it. The drum is rotated by
the cars wheels to a fixed speed. The brake is then applied to the drum until the engine
is no longer able to keep it spinning at the same speed. When this point is reached the
computer is able to calculate the power that the engine was producing.
This type of dyno is useful for calculating correct fuel and ignition settings at
particular engine speeds. Steady State testing however does not simulate the real
world. How often does a racing engine operate at a steady speed? Almost never, from
the start of a race to the finish the engine operates in an almost constant state of
acceleration or deceleration. The thermal dynamics of intake and exhaust flow,
combustion and mechanical components are much different under these conditions
than at a steady state.
Inertia Dyno :The cars wheels accelerate a drum, which has a known mass. The computer records
how fast the mass is accelerated and calculates the torque generated using Newton's
law - Force = Mass x Acceleration.
The computer then calculates the power using the formula-
Horsepower = Torgue x RPM
5252
Simple isn't it?
Another advantage of an Inertia dyno is that it never needs to be calibrated, as the
mass of the drum cannot alter.
How do I make sense of the Graph?
The graph I will give you after your run will have two lines on it, one represents
Horsepower and the other Torque.
Horsepower:This is measure of how much work your engine is capable of doing.
This is usually, but not always, the highest figure on the graph. Since it is a function
of torque and RPM it will generally rise steadily over the power run, ideally it should
be smooth and steady with no spikes or steps.
Torque:This is a measure of turning force that the drive wheels are applying to the ground.
Torque is what makes your car accelerate. If you have a lot of torque your car will
feel fast. Torque is measured in Ib.ft. To visualise 100 Ib.ft. of torque, imagine a bar
1 ft. long attached to the centre of your wheel hub, then put a 1001b. weight on the end.
The weight would make the wheel turn. The more weight you applied the more torque
would be generated. Again it is desirable to have a smooth torque curve, an almost
flat curve would make the car easier to drive.
The torque and power curves will always cross at 5252 RPM. Remember the
Horsepower calculation? Horsepower = Torque x RPM
5252
so the BHP and Torque figures will always be the same at 5252 RPM.
PECO '8 Rolling RoadThe rolling road that I will be testing your cars on is a DYNOJET 248x inertia dyno.
This is capable of accurately measuring up to 1800 BHP at speeds of up to 200MPH.
So no problem there then!
Most rolling roads have two small diameter rollers and the tyre sits between the
rollers. This encourages tyre deformation and wheel spin as most rollers that have
been used for any length of time have a polished shiny surface.
As you have probably noticed we have only one, massive, 4ft. diameter roller. The
tyre on your car will sit on top of the roller, that is almost a flat surface, as flat as most
roads anyway! The surface of the roller has been knurled so there is little or no chance
of any wheel spin.
What are you going to do to my car?First of all there are a few basic checks:
Check your oil level, top up if necessary.
Check your water level, top up if necessary.
Check your tyre pressures, a few PSI up is ok, a few PSI down is not.
I'll have a quick look around the car, if the engine's making any strange noises I'll
probably recommend you don't carry on.
Next I'll position the car on the rollers and tie it down so it can't move. We don't
want to end up in the River Mersey do we!
If your car has a towing eye that screws into the front bumper, I would be grateful if
you could find it and screw it in before bringing the car in.
In order for the computer to do its job it needs to know how fast the engine is going.
This used to be a simple task of clipping a lead to one of the plug leads. However lots
of cars these days have direct ignition and therefore haven't got any plug leads. If this
is the case with your car then I will have to try and find a low-tension ignition lead to
connect to. Not always easy but I will try. If your cars' ignition system is hidden by
plastic covers it would save time if you could remove them before bringing the car in.
Next job is to position a large cooling fan in front of the car and a smaller exhaust
extraction fan at the rear.
Well we're almost ready to go. I'll need to know from you what the maximum RPM
you want me to take it to and then we're off
I'll drive the car through the gears up to 4th gear and then slow down to about 1500
RPM, floor the throttle and wait for maximum RPM, lift off the throttle and apply the
brake on the roller. Within a couple of seconds the computer gives us a graph showing
your cars brake horsepower and torque.
I hope these notes give you a better understanding of what it's all about and you have
an enjoyably and interesting day.
Dave Jones. ![[Linked Image]](http://www.cruisewirral.com/gallery/uploads/01/05march/cruisewirral04015.jpg)