To be honest, Steve, measuring BHP on a rolling road is a minefield, and one of my soapbox subjects so I'm sorry for what follows.
You lose quite a lot of power in the tyres and rollers on a rolling road and unless the operator is careful to correct for these the "power at the flywheel" result won't be accurate.
Some people then say, well, sod all the corrections, let's quote power at the wheels. That's not accurate or meaningful either because the losses on a rolling road are far higher than on a real road and, importantly, they can vary between cars, and depending on factors such as how hard the car was strapped down on the rollong road.
The best method to obtain an accurate "flywheel" figure is to do a power run up to the rev limiter in a high gear. 4th is best on a manual as this is generally the 1:1 gear. Once the maximum revs have been reached, press the clutch, come off the power and let the road measure the losses as everything slows down again. This is called a "coastdown test". A modern rolling road will have the software to evaluate the losses during the coastdown and add them to the power that was measured on the way up, and you can end up with a power curve that's repeatable to within 5% or so.
The situation is more difficult with an automatic gearbox and the results will be less accurate as a result.
Having said all this, the main use of a rolling road is to determine if a small adjustment has made a difference, rather than to generate a figure to blag about down the pub
, and this only requires a relative measurement. It sounds like your car made an 8 BHP improvement measured on the same rolling road on the same day, and that means more to me than to say it has 244 BHP, because the absolute figure could be way out IME.
Kevin
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Topic: Real bhp (Read 1173 times)