Tony Posted June 13, 2006 Report Share Posted June 13, 2006 Limited as my knowledge is, i still attempt to understand all things modified mechanically, but i have a question . As i understand the Dyno measures the engines performance at the wheels and then the flywheel.. I thought this was done on a rolling road... Today i watched a Dyno being measured with a machine mounted directly at the rear drive shaft without the wheel fitted... How accurate can this be since there is no rolling resistance acting on the tyre Quote Link to comment Share on other sites More sharing options...
Adie Posted June 13, 2006 Report Share Posted June 13, 2006 I'm sure Mark will be able to explain this better.. But here's my little 'knowledge'.... The rolling road is the most less accurate with the readings as there are too many variables involved.. eg tyre pressure, the tyres heating therefore expanding etc. Also I think it uses something like water to cool it. Therefore this will heat up and again will not give an accurate reading. You could put a car on a rolling road for a power run and then do it again an hour later or so and will probably get different results. A dyno pack is a lot more accurate as the hubs are bolted directly to it. Whether it be front / rear or all wheel drive. The power figures are then calculated more accurately. What TDI use is a Rototest. This uses some sort of oil (cant remember what exactly) to cool it. So you should get the same results time and time again. It also measures the power , not calculating it. So it apparently gives around 5% less than a dyno pack. But is the most accurate. All figures are Rear Wheel Horse Power. Or front or all depending obviously on the car (rear wheel drive etc). The flywheel figure is then calculated from the power lost at the hubs through the transmission. Various people do it different ways so is not too accurate. Therefore you cant really compare peoples Bhp figures as they are not done on the same machine and flywheel figures are calculated (Or Guessed) differently... Also they tend to get exaggerated alot.. Quote Link to comment Share on other sites More sharing options...
Jap Devil Posted June 13, 2006 Report Share Posted June 13, 2006 There are three types of dynomometer: 1) Those which measure the power/torque at the flywheel. These are generally limited to the motor manufacturers who will test an engine "on the bench". 2) Hub dynos, which fit directly onto the hub 3) Rolling road, where the wheels turn a set of rollers. Out of these, the rolling road will give the truest indication of the power & torque as it would be if the car was on the road itself. Therefore values for the actual engine output can only be estimated from the transmission power/torque losses which vary from vehicle to vehicle and manual or auto transmission. Quote Link to comment Share on other sites More sharing options...
Adie Posted June 13, 2006 Report Share Posted June 13, 2006 Tony have a look on TDI website. On the home page it has a link saying Dyno Info. Have a read there mate. It should explain everything Look Here Quote Link to comment Share on other sites More sharing options...
Tony Posted June 14, 2006 Author Report Share Posted June 14, 2006 Tony have a look on TDI website. On the home page it has a link saying Dyno Info. Have a read there mate. It should explain everything Look Here Consider me fully educated, that link is superb.... no wonder tdiplc are leaders in their field! Quote Link to comment Share on other sites More sharing options...
TDIPLC Posted June 14, 2006 Report Share Posted June 14, 2006 Limited as my knowledge is, i still attempt to understand all things modified mechanically, but i have a question .As i understand the Dyno measures the engines performance at the wheels and then the flywheel.. I thought this was done on a rolling road... Today i watched a Dyno being measured with a machine mounted directly at the rear drive shaft without the wheel fitted... How accurate can this be since there is no rolling resistance acting on the tyre A "chassis dyno" is a generic term for a machine that applies a load and measures the torque of the engine whilst it is in the car. An "engine dyno" does the same thing but while the engine is out of the car on a test bench. There are quite a few different types of "chassis dyno" but they generally fall into 2 catagories of; 1) Measurement at the wheels (or more accurately described "at the tyres"), and 2) Measurement at the hubs (wheels removed). No chassis dyno can "measure" the flywheel torque or the transmission losses. At best they extrapolate, at worst they "guess" the losses then add that figure to those recorded at the wheels. We have used a "rolling road" (in fact several different brands) chassis dyno in our premises since about 1985 so are well aware of the limitations imposed by this method, which are namely the level of grip afforded by different tyre compounds and the change in the coefficient of friction as the tyre temperature changes constantly, and the change in tyre pressures that occurs proportionally with the tyre temperature. Both of these affect the power/torque recordings. An inexperienced or ignorant "tuner" may be pleased with his tuning results, but be unaware that his results are due to changes in the tyre grip, pressure and temperature, and nothing to do with his endeavours, therefore no improvements have been made and a lot of time and money has been wasted. To avoid this layer aggravation and potential for unhappiness, the way forward is for hub mounted dyno's which completely remove the tyre from the equation and hence provide 100% validatable results time after time. It's a shame that the best hub mounted dyno's are sooooo darned expensive Quote Link to comment Share on other sites More sharing options...
Tony Posted June 14, 2006 Author Report Share Posted June 14, 2006 I feel proud that my limited knowledge and question was a valid one... The Hub mounted Dyno's cost reflects the machines accuracy, if i were a customer i would respect that... For the record the explanation on your web site explains the complexities of Dyno very well..... Very well indeed Quote Link to comment Share on other sites More sharing options...
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