Pwheel V Peng for accuracy and repeatability?

[hartech]

If there are opinions on the relative accuracy or reliability of the results of rolling road tests for "wheel power" (Pwheel) compared to "engine power" (Peng or P norm) I would appreciate their comments.

Many Thanks,

Baz

[Porsche911R]

zero I would say. Are they more for before and after results when modding or remapping, the base figure then being a moot point.

I guess a hub dyno will be better than a RR dyno.

talk to some one like Charles Wright at Surry RR.

Edited by Porsche911R on Thursday 24th October 09:53

[ras62]

@ Wheel power is measured probably + or - 2% on a good dyno. Engine power is estimated, usually 10-15% higher than @wheel power. Repeatablity more important than accuracy?

[hartech]

Thanks guys, I was trying hard not to influence the replies in order to obtain different unbiased opinions but obviously left the request too vague.

I have actually used engine, road and roller dynos (air, water brake and eddy current) for nearly 50 years now (and we have one of the most reliable roller dyno set ups possible here at Hartech), but I have come across an issue in which someone else is using wheel power to validate performance set against manufacturers engine power which I am investigating.

I should have added that it is using a roller dyno to measure wheel power I was interested in and not directly fitted rear wheel dyno's.

I didn't want to say why as this might influence opinion and responses - so will still not for now - sorry.

I do appreciate that for measuring change with identical set-ups - it doesn't matter too much what method is used and I also agree that an engine dyno will measure engine output. However there are numerous pitfalls in all systems and I wondered how accurately others thought a measure of wheel power on a rolling road dyno would be to compare with an empirical manufacturers engine output and how reliable others thought the results and repeatabillity might be?

Baz

[ras62]

Given the shenanigans of numerous manufacturers involved in dieselgate I think it would be naive not to think all sorts of tricks are being employed to get the very best figures to give to joe public. Blueprinted motors, special fuel and oil, non standard mapping, who knows. If the rolling road figures are within 5% of manufacture numbers I would think that quite acceptable.

This link below is worth a read
https://www.wardsauto.com/news-analysis/sae-adopts...

[hartech]

That's interesting - I understand that an EU directive instructed manufacturers to limit their claimed BHP figures to the lowest number their worst production car in average condition with poor fuel in a generally average way - would always achieve - so their claims could never be over-stated (when they used to be) - but I would love to have that authenticated and find when it was introduced?

This could explain why we find older models in standard trim often do not achieve stated outputs whereas newer ones exceed it?


Baz

[ras62]

https://www.dynomitedynamometer.com/dyno-tech-talk...

Above link is a great description on the various standards that apply. SAE J1349. ECE standard is the same as the SAE J1349, but does not use mechanical efficiency in the calculations

[Murph7355]

hartech said:

That's interesting - I understand that an EU directive instructed manufacturers to limit their claimed BHP figures to the lowest number their worst production car in average condition with poor fuel in a generally average way - would always achieve - so their claims could never be over-stated (when they used to be) - but I would love to have that authenticated and find when it was introduced?

This could explain why we find older models in standard trim often do not achieve stated outputs whereas newer ones exceed it?

Baz

How old?

Replied on 911UK, but if someone's looking to this to talk to Porsche about, they're wasting their time IMO, unless the power is properly materially down which would suggest an issue.

Though judging by your username I suspect you know that