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06 - PB/DB - Power Mode

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Your car’s power output can be measured using the Power Mode. There are two parts to this process: the acceleration run, which gives you the power at the wheels minus the losses caused by tyre and air resistance. The second part of the test measures these losses and also estimates gearbox losses. The Power Mode is also an additional tool for car tuning, where access to a chassis dynamometer is not possible.

 

Note that this is an estimation of power, and as such when carried out correctly will probably be within 5% of the true figure. It is very important that the test is carried out on a completely flat road and the correct procedure is followed very carefully. Power output can only be measured on a car with a standard manual gearbox.

Power Testing

Please note that due to the nature of this test and the amount of space required, it is strongly recommended that such measurements are conducted on private roads.

Setting the Vehicle Weight

In order for accurate measurements to be made, the vehicle weight must first be entered via the Power Menu:

 

POWER MENU
UNITS
SET WEIGHT
SETUP
EXIT

The weight you enter must be as accurate as possible - for best results have the car weighed prior to carrying out any tests as even a small inaccuracy will not give correct power figures, a 10% error in weight will give a 10% error in power. Use the ▲▼ buttons to increase or decrease the weight value (Holding down the buttons increments/ decrements faster). Altering the units from the menu will change the weight values from lbs to kg, and the power values from bhp to kw.

 

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Power and losses runs should be carried out on level ground and always in the same direction, and it is recommended that power runs are conducted with the car in second gear. 

 

 

Power Runs

Once the vehicle weight has been set, a simple power run can be carried out to give engine output at the wheels. Put the car into second gear at a low RPM, 2000 RPM or less.

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Press OK, the next screen indicates that the PerformanceBox / DriftBox is ready to record the run:

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Once the car begins to accelerate, the power is being recorded:

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Accelerate to the top of the engine’s rev range, disengage the clutch and make a note of the car’s speed as this will be required during the losses run, then coast for a few seconds. The PerformanceBox / DriftBox unit will record the amount of power as soon as it recognises deceleration:

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Calculating Losses

 

So as to estimate power output figures at the flywheel, you will need to configure the amount of loss generated by tyre and air resistance. To do this requires a ‘coast-down’ test. It is recommended that this is carried out in third gear.

 

With the weight correctly entered, switch from the Power Run screen to the Losses Run screen using the ▲▼ buttons. The screen will display a similar initial instruction to the Power Run:

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Begin to accelerate, and press OK. Continue to accelerate to the top of the engine rev range.

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At the top of the rev range, disengage the clutch and put the gearbox into neutral. Once deceleration has begun the screen will display the recording information:

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Let the vehicle coast down to a speed a long way below the speed at which maximum power is likely to occur, then accelerate briefly to finish the run:

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Press OK to save the losses; pressing RESET will cancel the recorded losses so that you can start the process again. Losses are permanently saved, but you should generally carry this out on the same piece of road in the same direction as your acceleration runs. Note any small gradient can have a large effect on the measurement.

 

If you have not carried out any power tests at this point then accessing the Power Run screen will simply display the priming instructions. If you have already carried out power runs the results will now be displayed as output from the flywheel rather than the wheels. Any further power runs will display the results at the flywheel, until the RESET button is pressed when in the Losses Run screen.

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Pressing the RESET button when in the Power Run screen will clear the result in order for a new run to commence.

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Last modified
15:02, 14 May 2015

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