| Misleading power figures
Interesting to read the 'measured' power figures of both the One and the Cooper are approx. 10% higher than quoted. I assume that both of these were measured on a rolling road, 'at the wheel', and were then 'corrected' (i.e. fudged!) to get to an 'at the crank' figure. This fudge-factor is used to compensate for transmission losses, which are notoriously difficult to measure. It is normal practice to simply add 20-30% to the measured BHP, and call this the crank bhp. And don't start about the machine automatically calibrating, and measuring coast-down losses - these are also miss-leading. BMW will have hooked the engines up directly to a dyno, and measured true crank BHP, in strictly controlled conditions. Air temperature can make a large difference to measured BHP! 'Independent' tests are useful to measure differences between engines/mods/chips, and to get a feel for the shape of the torque curve. However, using these to say that a car produces more power than the manufacturer states must be seen to be foolish. I can supply a link to someone far more knowledgable on this subject if you want it..... |