TEST INFORMATION

All published tests have been conducted in a laboratory at RRI’s facility south of Stockholm Sweden. In some cases the test are performed by another organisation and then they are always supervised by personnel from RRI. If not tested in the RRI laboratory, the location is specified on the Certificate of Powertrain Performance™ (CPP). The R&D board of Rototest Research Institute is convinced that RRI’s test results are to become a world-wide standard for vehicle Powertrain Performance™ measurements and Powertrain Performance Graphs™ (PPG). All Certificates of Powertrain Performance™ are proudly produced with the highest quality level with the possibility to be verified by performance professionals around the world.

CONTENTS


Scientific usage of ROTOTEST chassis dynamometers

Dynamometer Calibration

Controlled test conditions

Powertrain Performance™ definition

Powertrain Performance Valuation™ (PPV) definition

TORQUE, SPEED AND POWER

Approximate equations

kW / Nm

PS (metric hp) / Nm

bhp (imperial hp) / lb-ft

Conversions

WHY POWERTRAIN PERFORMANCE™ MEASUREMENTS

Corrections of measured Powertrain Performance™

Test results - Rototest Certificate of Powertrain Performance™ (CPP)

ISO 1585 correction formula

Steady State test conditions

Torque presentation

Stated engine performance

Engine inlet temperature

Fuel

Total reduction

Selected gear

Four wheel drive (4WD)

Background information

Additional test information

Curb weight definition

Scientific usage of ROTOTEST chassis dynamometers To the top


The chassis dynamometer is the key element for producing Powertrain Performance™ measurements and respected Powertrain Performance Graphs™ (PPG). Rototest Research Institute has scientific demands on all published measurements and the chassis dynamometer has to produce correct and non-disputable results.

Dynamometer Calibration To the top


All tests are performed with a calibrated dynamometer (using a standardized procedure of dead weight calibration). Without a calibration there is no reference to the measured values. Without a reference there is nothing to assure consistency and ensure that measurements are compatible with those made elsewhere. For instance if power is measured and presented in bhp (imperial horsepower) a calibration will ensure that the values presented are compatible with the general definition of bhp, i.e. they are actually bhp and not something else. For more information about the dynamometer equipment please visit www.rototest.com.

Controlled test conditions To the top


To produce comparable and repeatable measurements it is of importance that the test conditions are kept within acceptable tolerances. Rototest Research Institute has a strict demand on test cell cooling capacity. The ROTOTEST dynamometers produce a strong airflow in accordance to the absorbed load. For "after-cooling" (no load and/or speed on the dynamometers) and for additional airflow, electrical fans are used. Dedicated electrical fans are used for intercoolers.

Powertrain Performance™ definition To the top


Rototest Research Institute defines Powertrain Performance™ as the engine performance reduced by the losses through the powertrain (transmission, differential, joints, etc.). Simplified - Powertrain Performance™ is the performance available to the wheels.

Powertrain Performance Valuation™ (PPV) definition To the top


The Powertrain Performance Valuation™, PPV (power rate, torque rate) is the exchange rate between the claimed engine performance (by the producer, auto manufacturer, etc.) and the actual performance available to the wheels.

Clarifications:
There should always be a difference between the two due to engine performance variations and transmission losses. Comparing the graphs (claimed performance and actual performance) for power and torque is a good way to see if promised performance exists over the whole speed range and not only at the maximum points. For more information see the white paper "Why powertrain performance measurements". [White papers...]

TORQUE, SPEED AND POWER To the top


The chassis dynamometer measures drive wheel torque [Nm, lb-ft, kgm] and drive wheel speed [1/min (rpm)] (and/or engine speed [1/min (rpm)] where applicable). The physical relationship between Torque, Speed and Power is that torque times speed results in power. The equation using SI units is:

P = M x w

where
P is power, expressed in [W] Watt
M is torque, expressed in [Nm] Newton metre
w is angular velocity, expressed in [rad/s] radians / second

Approximate equations To the top


To allow easier calculation there are a number of approximate equations available of which a few are presented below. The equations will introduce a small error as they are using a limited number of decimals and should not be used other than when approximate values are enough.

kW / Nm To the top


Power [kW] = Torque [Nm] x Speed [1/min] / 9549

Torque [Nm] = 9549 x Power [kW] / Speed [1/min]

PS (metric hp) / Nm To the top


Power [PS] = Torque [Nm] x Speed [1/min] / 7019

Torque [Nm] = 7019 x Power [PS] / Speed [1/min]

bhp (imperial hp) / lb-ft To the top


Power [bhp] = Torque [lb-ft] x Speed [1/min] / 5252

Torque [lb-ft] = 5252 x Power [bhp] / Speed [1/min]

Conversions To the top


1 kW ≈ 1.34 bhp (imperial hp)
1 kW ≈ 1.36 PS (metric hp)
1 bhp (imperial hp) ≈ 1.015 PS (metric hp)
1 lb-ft ≈ 1.36 Nm
1 Nm ≈ 0.735 lb-ft

NOTE!
Performance Graphs (torque and power) always have the relations above. Graphs that do not fulfill these relations are based on bad measurements and/or bad "after adjustments" and may indicate intentional disinformation (regardless of whether they are called Performance Curves, Power Graphs, Power curves, Power and Torque Curves, Dyno Runs, Dyno Graphs or Dyno Curves).

WHY POWERTRAIN PERFORMANCE™ MEASUREMENTS To the top


To address why Powertrain Performance™ should be measured, Rototest Research Institute has published a White Paper where Powertrain Performance™ measurements versus engine performance is discussed. The paper also includes statistical data where stated engine performance is compared to Powertrain Performance™. [more...]

Corrections of measured Powertrain Performance™ To the top


Engine maximum output is often dependent of ambient conditions, such as atmospheric pressure, (higher pressure more power) inlet temperature (lower temperature more power) and air relative humidity (less humidity more power). These parameters are almost impossible to make constant during laboratory tests. Because of that there are standards for correction of the atmospheric conditions. There are several standards for correction of engine performance in the "automotive society". DIN 70020, (Deutsches Institut für Normung) ISO 1585, (International Organization for Standardization) etc.

NOTE!
All standard corrections give approximate results. According to the ISO 1585 standard, corrections for inlet temperature are restricted between +15° to +35°C. Non-corrected measurements values must be present in any presentation of Powertrain Performance™ results. This is an important quality factor to allow others to judge the significance of the presented corrections.

NOTE!
Modern computer controlled engines have the possibility to self-correct for ambient conditions (increase, decrease power). This is especially true for forced induction (turbo, compressor, etc) equipped engines where the boost can be controlled to absolute levels (instead of relative). Applying a correction on engines with a self-correction feature is incorrect and not allowed depending on which standard that is used.

Test results - Rototest Certificate of Powertrain Performance™ (CPP) To the top


Page one: Powertrain Performance Graphs™ (PPGs) with drive wheel torque and wheel power during Steady State. Stated engine performance during Steady State conditions is in some cases presented for comparison.
Page two: Background information. Power and torque corrections for spark ignition naturally aspirated gasoline engines are made according to ISO 1585 standards.

ISO 1585 correction formula To the top


fc = ( 990 / p )^1.2 x (( T + 273 ) / 298 )^0.6

where
fc is the correction factor applied to power and torque
p is the dry absolute atmospheric pressure, expressed in mbar
T is the inlet air temperature, expressed in °C

NOTE!
8 mbar higher atmospheric pressure ≈ 1% more power
5°C lower inlet temperature ≈ 1% more power

Steady State test conditions To the top


Steady State is the standard test condition used by the automotive manufacturers. The Powertrain Performance™ at Steady State is measured at different constant engine speeds. Unless otherwise stated all tests are conducted at Steady State, i.e. at a fixed engine speed, and the engine is kept at full load (wide open throttle, WOT) until certain conditions are met when the measurements are taken. The engine speed is then changed to the next engine speed usually about 500 rpm apart and/or closer at the expected peak power and torque. The tests conducted by RRI follow the same principal procedure with one important difference — the test equipment on which the tests are conducted. While the engine manufacturer states peak power and peak torque for the engine (at the flywheel) this requires the engine to be tested separately in an engine dynamometer. RRI uses a dynamometer from Rototest that measures the Powertrain Performance™ produced at the wheel hubs. The Rototest dynamometer is very similar to an engine dynamometer with the only difference that it is meant to measure Powertrain Performance™ instead of engine performance.

NOTE!
  • Test point times at Steady State less than approx. 3 seconds are not appropriate due to normal engine output variations.
  • A longer test point time gives more information about engine cooling capacity.
  • The measurement points are joined by a spline only for display purposes. There is no information about Steady State Powertrain Performance™ between the measurement points.
  • At Steady State there is no performance influence due to the inertia of the powertrain (e.g. engine flywheel).
  • Steady State measurements are generally not comparable with measurements during acceleration conditions! Measurements of Powertrain Performance™ during acceleration or dynamic conditions will always be affected by the powertrain inertia due to the energy consumed (stored) in the rotational inertia of the powertrain components, such as the engine flywheel. Acceleration speeds less than 100 engine rpm/second (1000 to 7000 engine rpm in a minute) are approximately comparable to steady state measurements.
  • Performance measurements during acceleration with varying acceleration rates are not comparable in any way (results from rolling roads, hub dynamometers and engine dynamometers with no accurate speed control for constant acceleration rates) There are also, in many cases, a lack of correction methods for minor fluctuations in the acceleration rate.


  • Torque presentation To the top


    The sum of the torques measured at each wheel hub is presented as total drive wheel torque divided by the total transmission reduction (i.e. the gear ratio times the final drive ratio)

    Stated engine performance To the top


    Where applicable, the engine stated performance is plotted together with the Powertrain Performance™ in the Powertrain Performance Graph™ (PPG) as comparison. The source of the stated engine performance is always declared. The source is commonly the auto manufacturer, a respected motor magazine, or specified otherwise.

    Engine inlet temperature To the top


    The engine inlet temperature is measured in the inlet duct to the engine before the air filter. Ambient temperature is only as information of the test cell temperature and may not be representative and therefore not valid for correction.

    Fuel To the top


    The fuel used is specified on the Certificate of Powertrain Performance™ (CPP) Minor differences in performance may occur due to different fuel specifications.

    NOTE!
    Use of low density diesel fuels such as Swedish low sulfur diesel, may decrease performance by 3-5%. Low octane fuels used in knock sensitive engines is also a factor to be aware of. Alcohol fuels such as E85, (mix of 85% ethanol and 15 % gasoline) can be used in turbo engines to increase power compared with gasoline (+20% - +30%) due to higher resistance to knocking and possibilities to use the fuel as internal cooling. Use of higher octane fuels in knock in-sensitive engines (most standard engines) does not influence the engine performance.

    Total reduction To the top


    The total transmission reduction (total transmission reduction) is the ratio between engine speed and wheel speed. In most cases there is a gearbox ratio and a final drive ratio. In some cases for 4WD there is a different total transmission reduction between the front axle and the rear axle. In these cases the total transmission reduction is presented as the average transmission ratio.

    Selected gear To the top


    The gear with closest relation to 1:1 (“straight through”) in gearbox ratio is preferred for Powertrain Performance™ measurements. The transmission losses vary with torque input, speed and number of gears involved in the transmission. On the Certificates of Powertrain Performance™ (CPP) the used gear information is always present in form of a total transmission reduction with each measurement sequence. For test vehicles with automatic gearboxes with slipping torque converters the average wheel power and engine speed is used for the torque calculations.

    Four wheel drive (4WD) To the top


    The systems used in four-wheel drive cars can generally be divided into two main groups; 4WD systems using a centre differential and 4WD systems using a centre coupling (also known as 2+2WD). The two groups can be further divided depending on the type of differential or coupling. The test procedure for each type is chosen depending on the 4WD system’s capability.

    4WD group Differential / Coupling Functionality Normal test procedure
    Centre differential
    (4WD)
    Conventional open differential with or without limited-slip functionality Both axles can drive up to the limit of the differential 50-50 % distribution
    Centre differential
    (4WD)
    Conventionally planetary differential with or without limited-slip functionality Both axles can drive with the distribution according to the planetary gearbox (or the limited-slip clutch) Distribution according to specification
    Centre coupling
    (2+2WD)
    Viscous coupling One axle is primary and drives secondary axle through the coupling Primary axle full distribution
    Centre coupling
    (2+2WD)
    Mechanically or electronically controlled clutch One axle is primary and drives secondary axle through the coupling Primary axle full distribution or according to specification

    This information is in no way a recommendation for use with any dynamometer system. Please use the manufacturer system manual for safety and testing issues.

    Background information To the top


    Parameters below are published because they have an influence of the Powertrain Performance™ results and due to the fact that performance corrections are not an "absolute science".

    Background information parameters include:

    Atmospheric pressure [mbar]
    Ambient temperature [°C]
    Air relative humidity [%]
    Engine inlet temperature [°C]
    Engine oil temperature [°C]
    Engine speed [rpm]
    Measurement time [s]

    Additional test information To the top


    - All tests are conducted with a warmed up test vehicle powertrain.
    - All unnecessary electrical consumers are switched off.
    - AC and power steering is not in use.
    - Brakes are controlled for dragging (the wheels are removed).
    - Tests conducted prior to April 2008 have generally been made with the car’s engine bonnet open. Tests conducted after this date are generally made with the car’s engine bonnet closed or partially open (safety catch engaged).

    Curb weight definition To the top


    All test cars are weighted at Rototest Research Institute with full fuel tank and with all other fluids. All standard equipment is present (spare wheel, tools etc). Car weight may differ due to equipment, air condition, aluminium rims, type of spare wheel, type of seats etc. No driver weight is added.