March 12, 2010

The Game of Deception - Horse power [Hp] or Donkey power [Dp] that's the question!

In this the third of a total of four issues, formed as four different chapters, the RRI Column's Sven Andersson will try to give you answers for most of the common concerns about performance measurements. This particular issue deals with fantasy losses in the transmission.

Chapter 3

Q8: What is the second worst case dyno concept?

A8: The inertia, uncontrolled acceleration concept combined with a tyre grip dependable rolling road is frighteningly common and is also a real assault at true measurements of Powertrain Performance.

Q9: How does the use of inadequate measurement equipment influence the claims for Powertrain Performance™ in general?

A9: Measurement equipment with large result tolerances, such as tyre grip dependable rolling roads, or garage grade hub dynos without adequate measurement devices for torque and speed are useful tools for performance deception in the following ways:

1) Several tests are performed and since all of them give different results, the “good results” can be sorted out. The selected “good results” are then used as evidence for performance improvements.

2) Chassis dyno manufacturers who claim measurement of engine power. These false claims are based on lack of physical and powertrain knowledge. For more information please see The RRI white paper "Why powertrain performance measurements?". These false claims are also used for attempts to compare auto manufacturer’s statements for engine power at a steady state (please read more about steady state and steady rate measurements below).

NOTE! With a chassis dynamometer it is only possible to measure Powertrain Performance.

Q10: Are there fantasy estimations of transmission losses?

A10: YES! Another way to deceive is to use a garage grade dyno with built in systems for adding transmission loss factors to the Powertrain Performance measurements for "engine power" statements. In a few cases the transmission factors claim to originate from some of the auto manufacturers!

NOTE! Claims for the worst case of transmission losses, for vehicles with automatic transmissions and 4WD over 15%, are almost always untrue.

WARNING! Chassis dynamometers, (garage grade rolling roads and hub dynos) with these built-in features they are not capable of issuing truthful Professional Performance Graphs, PPG.

NOTE! The transmission losses are not in a fixed proportion to the engine power. The losses change with engine load and speed, used gear etc. and also with the individual tested vehicle . A fixed factor for the transmission losses are always an approximation. The transmission losses have a variation of approximate 2% between different vehicle individuals of the same vehicle specification and even more at different loads and speeds.

NOTE! If users of chassis dynamometers make a statement, about the engine performance with a published figure for used transmission losses (5-12%, depending on transmission design), that is satisfactory, as an approximate statement for engine power.

RECOMMENDATIONS! Use only professional performance suppliers, using test equipment, which produces test results, according to Best Known Practice, BKP, which can be checked by other performance professionals. Powertrain Performance™ measurements on professional test equipment will only produce small variations in test results (within a few %, including both measurement tolerances and other variations).

WARNING! A performance statement that cannot be reproduced by others despite cause is a strong warning for potential deceivers and "Donkey power" [Dp] (see A16) results.

Q11: Is changing tyres and/or vehicle position between test runs a quality factor for rolling roads?

A11: YES! This is an issue on tyre dependent rolling roads. Different tyres will give different results and these can be used for falsifying performance results. Rolling roads are also sensitive to the position of the tyres on the roller, different positions will give different traction and the traction will differ with the applied torque. These two circumstances are two of the main obstacles for accurate measurements on a rolling road; the dependence of tyre traction and the dependence on tyre-roller position. These two conditions are both open for misleading performance results.

Q12: Is the location of engine inlet temperature measurement important?

A12: YES! The engine inlet temperature should be measured in the inlet duct to the engine before the air filter. If the inlet temperature is measured after the air filter or even closer to the engine inlet channels the temperature correction will be to large (more power) due to a higher inlet temperature.

ISO 1585 correction formula:

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

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

Sven Andersson

The article, The Game of Deception, Horse Power [Hp] or Donkey power [Dp] that's the question! chapter 1-3, by Sven Andersson, March 2010 is free to download for non-commercial purposes.

[ Download ] (9 pages, 230 kb)