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Discussion Starter #1
Hi guys,
Here is some interesting info I've put together :
We all want to believe that a power figure is accurate (if its your car & its a high one!)
Here are some things to look for / ask when supplied with a printout:
There are 3 areas which can result in the FW power figures being way off the mark.
1) The rolling road only measures torque (usually expressed in lb/ft). To convert this to power at any point on the graph its internal calculator multifpies this by the rpm then devides by 5250 (this figure never changes). If you check this theory you can see this always tallys up . The power inaccurracy occurs like this; If the initial engine rpm to roller speed calibration is 'out' the power shows higher than is. eg If torque at say 6000rpm is say 200lbft then power is 200 x 6000 divided by 5250 =228bhp. However if in reality the true
rpm at this torque were only 5500 then power will be 200x5500 devided by 5250 =209bhp!
The tell tale sign is a graph showing peak torque (and power) at unusually high rpm.
The peak torque doesnt artificilly inflate but the power (bhp)does!
2) Rollers only measure torque at wheels,not the FW. sadly we all want the FW figure as is more impressive and compares to the manufacturers figure (to be fair our US buddys
use WHP more ).The calulation and correction to flywheel figure is where it can again
get inflated! A FWD car will lose around 13% tranmission & tyres(mostly tyres)
therefore multiply the'wheels power by 1.15 to give FW figure. Its very important to get a copy of the power at wheels to establish what percent correcion has been added on!
3)Ambient pressure and temp play a role in power output.Low temp and high pressure give more power and should be entered into the software each time . As an example if you 'tell it' the temp is 25 deg. C and 980Mbar when its actually 5deg. C and 1050Mbar
you will get an impressive readout! SAE & Din correction helps calculate with consideration of these parameters.
Hope this helps a bit
Best Regards Roland GT Tuning Ltd
 

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hey lightbulb head....
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1,305 Posts
how many mini owners are even gonna try and work that out?

dosent help me because mine running a 1hp steam engine anyway! only got 1 gear!!


choo choo
 

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roland2003 said:
Hi guys,
Here is some interesting info I've put together :
We all want to believe that a power figure is accurate (if its your car & its a high one!)
Here are some things to look for / ask when supplied with a printout:
There are 3 areas which can result in the FW power figures being way off the mark.
1) The rolling road only measures torque (usually expressed in lb/ft). To convert this to power at any point on the graph its internal calculator multifpies this by the rpm then devides by 5250 (this figure never changes). If you check this theory you can see this always tallys up . The power inaccurracy occurs like this; If the initial engine rpm to roller speed calibration is 'out' the power shows higher than is. eg If torque at say 6000rpm is say 200lbft then power is 200 x 6000 divided by 5250 =228bhp. However if in reality the true
rpm at this torque were only 5500 then power will be 200x5500 devided by 5250 =209bhp!
The tell tale sign is a graph showing peak torque (and power) at unusually high rpm.
The peak torque doesnt artificilly inflate but the power (bhp)does!
2) Rollers only measure torque at wheels,not the FW. sadly we all want the FW figure as is more impressive and compares to the manufacturers figure (to be fair our US buddys
use WHP more ).The calulation and correction to flywheel figure is where it can again
get inflated! A FWD car will lose around 13% tranmission & tyres(mostly tyres)
therefore multiply the'wheels power by 1.15 to give FW figure. Its very important to get a copy of the power at wheels to establish what percent correcion has been added on!
3)Ambient pressure and temp play a role in power output.Low temp and high pressure give more power and should be entered into the software each time . As an example if you 'tell it' the temp is 25 deg. C and 980Mbar when its actually 5deg. C and 1050Mbar
you will get an impressive readout! SAE & Din correction helps calculate with consideration of these parameters.
Hope this helps a bit
Best Regards Roland GT Tuning Ltd
The drag loss does not work that way. It's actually exponential with RPM, not a linear % loss. I agree with the rest though, except to say that RPM can also be taken directly off the engine and power plotted against that, hence eliminating the wheel sourced RPM error and giving more accurate wheel torque.

Adam.
 

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hey lightbulb head....
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if a company like chip tuning tell me my car is putting out 127 bhp then im not even going to question them! i havent got time to be working out all those sums!!


just believe the company that owns the rolling road, they are the experts so dont question em with your bhp figure
 

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Discussion Starter #5
Yes but the percentage is pretty accurate at max power peak. Their is only one true way to establish the losses across the range. That is to measure the engine power on a dyno
then measure the wheels power on the rollers, take one from the other & you have the losses. Incidently putting the car in neutral and inverting the drag is not ideal as does not include much of the gearbox losses :) Direct tacho link to roller speed is good.
 

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Kinda understand it, and the maths isn't that hard ;)

I showed my RR graphs to Ray West today, and although they are healthy and nice and linear, the figures are down, but not massively ... so on the whole not too fussed in my instance.

I bought the car used so it could even be the simple fact it was never run in properly and will always be alittle weak apparently :confused:
 

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roland2003 said:
Yes but the percentage is pretty accurate at max power peak. Their is only one true way to establish the losses across the range. That is to measure the engine power on a dyno
then measure the wheels power on the rollers, take one from the other & you have the losses. Incidently putting the car in neutral and inverting the drag is not ideal as does not include much of the gearbox losses :) Direct tacho link to roller speed is good.
True, except again with the losses it really does depend on RPM. If say max power on a stock car is at 5000 rpm, and you modify it to attain max power at 8000 rpm for example, drag losses will be significantly higher than the % loss calculated on the stock car at 5000 rpm.

Adam.
 

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LordNikon said:
I bought the car used so it could even be the simple fact it was never run in properly and will always be alittle weak apparently :confused:
I have the same problem with my MCS, but I'm happy now the conversion's been done! :D
 

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Discussion Starter #10
so do your new power run and multiply this wheels figure by 1.15 and will still be pretty close .
15% of a higher figure is more than 15% of a lower figure (obviously). :)
 
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