How many Kilowatts is it?

21 May 2015 Stories of a Modern Day Mechanic - PJT All,

Blog  Two: 

So I thought I would run though the basics of my day on the phone.
This is going to be focusing mainly on the phone calls I receive everyday and a very specific topic that I feel I repeat every single hour.

This topic would have to be one of those simple things, a very simple thing once its understood correctly its easy to explain but it kills me a little bit in side every time someone picks me up or points out that I’m wrong with my power figures. (I’m not wrong when I quote figures either, if anything I am more on the conservative side.)

….. I am of course talking about power measurements, more specifically dyno power readings. Even more specifically, the dyno power readings from our chassis dynamometer.

To give you an idea, just the other day I took two of these customer phone calls with my mother standing behind me.
I took her comments after the phone calls as a bit of compliment “…I have known you for 30 years and I know how impatient you are, to hear you break that down and explained exact same thing twice in 20 minutes, without even a hit of frustration I’m impressed…” It’s really not a claim to fame due to the fact my mother was the one making the statement, but for someone as impatient as myself it was a pretty great compliment as I do love my job and respect our customers and love educating them further.

Having said the above point, I did mention it kill’s me a little bit inside. This is not because I have to educate people, as you no doubt have guessed from the above statement I enjoy it. It’s due to the total misconception of factory quoted Kilowatt or Power figures Versus what everyone else comes up with as rear wheel power and torque when measured with a Chassis Dynamometer.

Its very, very, very simple we have a Dynamometer, or Dyno for short and here is a basic quick rundown.

When we place the vehicle on the dyno we enter all the vehicle details and then enter all the relevant information, like air temp, barometric pressure, tyre pressure and many other important factors to keep the vehicles true power consistent as possible. (this is important information to keep the readings honest.)

We strap the vehicle to the dyno: (I am going to use a rear wheel drive car, automatic Turbo diesel as an example.)

  • The driving wheels are dropped into the rear rollers. (Imagine its like a rolling road, or a push bike on a trainer.)
  •  A chin hook and loop strap is tied over the diff or on a solid rear suspension tie down point and this is secured in such a way that the forward force of the vehicle tightens the grip of the tyre to the roller and maintains good grip throughout the dyno run.
  •  We start with putting the vehicle under load, simulating a steep hill at low RPM, then we gradually increase the road speed until 100kph, check the speedo and tacho and make final adjustments to settings. 
  •  The Dyno is fully computer controlled, so it’s simply a matter holding at W.O.T (wide open throttle) for a couple of seconds then the Dyno automatically ramps up to maximum RPM. Most dyno runs take around 6-8 seconds, then the graph is completed and maximum power torque are displayed.

The above example is only a very small part of dyno tuning, realistically its probable the least important part. However, this is how we measure the power at the wheels or as we call it rear wheel power.

Now our friends at the factory be it Ford, Holden, Nissan or Toyota they all have one major thing in common, this is of course how they measure and market power readings from their engines.

From a marketing standpoint a larger number always sounds better and a number higher than the previous model is what consumers expect, so by reading the power at the flywheel on an engine dyno the number will always be higher.

To measure power and torque on an Engine Dynomometer. This means no straps, no rollers, its direct drive from the engine’s flywheel or torque plate to the dyno’s retarder .
The engine is placed under load the same as the chassis dyno, however the “numbers” end up a lot different.

Now the reason why these measurements are higher is due to the fact there is no “drive train” loss.
This of course is the transmission, the differential, wheel bearings , wheels and basically anything that causes additional friction is a loss, this includes the size of the drive tyres (bigger wheels and tyres = more loss).

So when I quote a customer on the phone power figures, lets use the Unichip plug and play unit PPTOY200.3. (200 series Automatic 6 speed V8 Turbo Diesel Land Cruiser.)

Our advertised before power figure is 144rwkw at 3400rpm (although we have seen some of these as low as 110kw@ the wheels, this is found on our web page and has a dyno graph to display the power and torque.) however the factory quoted power is at 195kw at 3400rpm. (This is simply sated on the Toyota web page.) This is a huge difference of 50kw! And the ONLY difference is where the measurement is taken from…. Kind of funny when you think about it… But don’t despair think of the owners of the older 100 series V8 Petrol, Factory quoted power of 180kw and the best we have seen is around 90kw @ the wheels, with a nearly identical driveline to the 200 series??

(FYI, torque figures suffer from the same type of loss and can be just as confusing to some owners this is also due to the same effect of drive drain loss.)

Now don’t get me wrong I’m not saying any of the manufactures are wrong or dodgy, in fact if I could truthfully display flywheel settings using our dyno and use that as a selling point I would in a heart beat. It would not only sound larger so the consumers will think its better, it would weed out a lot of the confusion.

But this is not the case. So the next best thing is to educate people over the phone and direct them to this blog.