Interpreting power curve

[Number_Cruncher]

As you may know, I'm extremely sceptical about the way losses are estimated by dyno operators, and I'm also fairly sceptical about the measuring technique many of them use to begin with.

What Steve's plot shows is that the gradients where the torque lines cross, especially for the higher gears, isn't large. This means that small errors in local road gradient can cause problems for the inclinometer method.

An interesting point in Steve's first graph (which is in the spreadsheet too) is that the tractive effort curves all fit together under the smooth curve you would get with a CVT operated at maximum power - the individual curves are tangent to this ideal curve at the maximum power engine speed.

>>Losses are exponential to the power supplied.

Really? I usually work with the assumption that they are proportional, or, in the case of frictional losses for lip seals or bearing pre-loads, a simple constant torque.

 

[stevesey]

How did you calculate the transmission losses, I thought the graphs were before and after remap?

I took them as dyno & flywheel - the higher ones match the expected 120bhp output.

 

[wemorgan]

I know Adam recently had his Polo remapped at Stealth Racing, so I too assumed the graphs were before/after curves.

 

[stevesey]

Ok - too late to edit my post now.

Changing gear at higher revs post re-map makes sense.

 

[stevesey]

To squeeze under the size limit of this site, it uses the ultra compression option in 7-zip. Sorry, I should have mentioned that.

Remembered one of my VMs has 7-zip on so can access now - useful sheet. Slightly optimisitic on my focus - 1 sec quicker 0-60 than the ford figures - but the sheet makes an approximation of the power curve from 2 figures, so not bad - thanks NC.

 

[Number_Cruncher]

>>makes an approximation of the power curve from 2 figures, so not bad

Yes, it uses the fact that at maximum power, you know not only the torque, but also the gradient of the torque curve with respect to engine speed - and vice versa at maximum torque.

This approximation to the torque and power curves can be a weakness of the spreadsheet, and, if you have better power and torque data, it would be better to use them directly.

The other large weakness of the spreadsheet that I'm aware of!, is that it makes no allowance for the inertia of the drivetrain, and this may explain at least some of the sheet's optimism.

To properly include drivetrain inertia, the spreadsheet would need to use a different "effective" mass for the car for each gear.

 

[Adam230K]

Stevesey; Yes they are before/after curves after a remap, sorry I probably should have said this earlier.

DM: That article link was very useful and it makes alot of sense. But of course I can also deduce from it that if I hit the optimal shift points I should be able to accelerate quicker from x mph to y mph, which is why maybe I can just do timed runs between certain speeds? The bigger interval of speed the more accurate it will be?

Oh and by the way, I called up the guys who remaped my car and they told me that they disabled my EGR valve , one less job to worry about. I guess I should clean my intake to increase the performance/mpg because its had 60k miles of the EGR throwing crap at it?

 

[stevesey]

Might still be worth blanking the EGR - just incase it is leaking, not closed properly. Depends how easy a job it is (mines disconnected at present - but no one seems to do blanking plates, so I'm planning to make one up at some point).

 

[Adam230K]

I dont understand a great deal about it but I did read somewhere that if I blanked it manually it will throw the EML light and give error codes because there's some air content probes somewhere around it this is just a vague recollection though

 

[Dieselman]

I dont understand a great deal about it but I did read somewhere that if I blanked it manually it will throw the EML light and give error codes because there's some air content probes somewhere around it this is just a vague recollection though

It uses the MAF to detect the volume of ingested air, which should be less when the EGR valve opens.