Nick Hill
15-02-2006, 16:51
Firstly I would like to say a very big thank you to the Williams Clio Club and organisation for a great day. I thoroughly enjoyed it and can see from various posts that most other folk did as well. My landlord the farmer has not even been to see me yet so that is definately a good sign that he was not upset in any way. Which means more R/R days to come.
Secondally I have written a brief summary to rolling road power figures which may help with your graphs.
I had a feeling when I opted to put Observed and Corrected power on our graph print outs that this would stir up some debate about rolling road figures and can now hopefully enlighten you to what the power figures are all about.
On the graphs we gave to customers you will see both Obs-Pwr and Hp.
Starting with the Obs-Pwr curve.
This is the observed (recorded) power the car has made on the particular day with whatever temperature, barometric pressure and relative humidity on that day. This figure will change throughout the year depending on the weather conditions of the day. In all reality it is the power you have on the day and you will have more power in the winter than in the summer, as we all now from how your car feels different in the summer from the winter.
That’s observed power simple and straightforward, now for Hp.
Hp on the graph is what is known as a corrected figure. This means that the observed figure is corrected to SAE (standard automotive excepted) industry standard. SAE - Atmospheric correction is applied using the more conservative (than Standard) SAE J1349 correction curves, based on: “77 degrees Fahrenheit Inlet Air temperature, 99 kilopascals (29.38 inches of Mercury barometric pressure @ 32F), and Dry Air.” SAE is not the only correction available with our logging system, we can also choose from Standard, DIN, JIS, ECE, and J1995. These are all slightly differing correction factors.
Basically this means that if possible an engine were to be tested on exactly the same equipment whether it be Greenland to Africa (temp) Sea level To the Himalayas (barometric pressure) or The rain forest of South America to the Sahara (relative humidity) All of these different conditions will give different observed power figures as will summer to winter in Derbyshire. The SAE correction is therefore applied to the observed power and theoretically no matter where or when the engine has been tested theses corrected figures will be the same.
This Hp is the figure that we always use for power and torque when development work is undertaken as we can always be certain that gains made are real gains made.
When having a Rolling Road test whether with us or elsewhere you need to know if the figures being given to you are on the day (observed) or corrected because as you can see from the graphs posted on the site you could have a deal of variation and if you don’t now which you have been quoted how do you now exactly where you are?
If you are having mods done to your car that are being carried out on the same day and a before and after figure is required, it makes no odds which power figure you use. Hopefully you are gaining power whichever. If you want to do other mods throughout the year then you need to go on corrected power so that future changes can be quantified.
I hope that this explanation gives you an insight and better understanding of the figures given out from Rolling Roads and helps you understand the reasons why we use corrected figures in the industry.
Secondally I have written a brief summary to rolling road power figures which may help with your graphs.
I had a feeling when I opted to put Observed and Corrected power on our graph print outs that this would stir up some debate about rolling road figures and can now hopefully enlighten you to what the power figures are all about.
On the graphs we gave to customers you will see both Obs-Pwr and Hp.
Starting with the Obs-Pwr curve.
This is the observed (recorded) power the car has made on the particular day with whatever temperature, barometric pressure and relative humidity on that day. This figure will change throughout the year depending on the weather conditions of the day. In all reality it is the power you have on the day and you will have more power in the winter than in the summer, as we all now from how your car feels different in the summer from the winter.
That’s observed power simple and straightforward, now for Hp.
Hp on the graph is what is known as a corrected figure. This means that the observed figure is corrected to SAE (standard automotive excepted) industry standard. SAE - Atmospheric correction is applied using the more conservative (than Standard) SAE J1349 correction curves, based on: “77 degrees Fahrenheit Inlet Air temperature, 99 kilopascals (29.38 inches of Mercury barometric pressure @ 32F), and Dry Air.” SAE is not the only correction available with our logging system, we can also choose from Standard, DIN, JIS, ECE, and J1995. These are all slightly differing correction factors.
Basically this means that if possible an engine were to be tested on exactly the same equipment whether it be Greenland to Africa (temp) Sea level To the Himalayas (barometric pressure) or The rain forest of South America to the Sahara (relative humidity) All of these different conditions will give different observed power figures as will summer to winter in Derbyshire. The SAE correction is therefore applied to the observed power and theoretically no matter where or when the engine has been tested theses corrected figures will be the same.
This Hp is the figure that we always use for power and torque when development work is undertaken as we can always be certain that gains made are real gains made.
When having a Rolling Road test whether with us or elsewhere you need to know if the figures being given to you are on the day (observed) or corrected because as you can see from the graphs posted on the site you could have a deal of variation and if you don’t now which you have been quoted how do you now exactly where you are?
If you are having mods done to your car that are being carried out on the same day and a before and after figure is required, it makes no odds which power figure you use. Hopefully you are gaining power whichever. If you want to do other mods throughout the year then you need to go on corrected power so that future changes can be quantified.
I hope that this explanation gives you an insight and better understanding of the figures given out from Rolling Roads and helps you understand the reasons why we use corrected figures in the industry.