[netopyer]

i want to avoid misunderstanding here :



in europe, common practice is to measure/provide crank HP, in US it seems to me that everyone is only talking about WHP

every dyno here is able to put out a result which includes crank HP and wheel HP.. the difference between them are power losses in drivetrain etc etc..



just to provide one example of graph with all above mentioned , i found this . hope that helps everyone to understand:

http://www3.sympatico.ca/mark.dean/dyno2.JPG

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[flash]

the problem is that it is NOT as accurate as merely measuring at the wheels. there are too many variables in drivetrain loss. tire size, weight, diameter, and pressure can easily change things. transaxle temp too. even the gear in which you do the runs can make changes. there are other things too. i've measured drivetrain loss and seen it differ between cars by as much as 10hp.



i cannot say this enough. you cannot expect to "calculate" anything. that is only an estimate. just measure what you get.



as an average, drivetrain loss on a 968 is between 30 and 40hp. it is not a percentage as many would think. friction does play a part, and it does increase as load increases (i.e. higher output engines making more friction) but it's minimal.



so, for example, if your "calculation" only figures 20hp loss, then you'd be pretty much right there showing 220 at the crank, because you could easily have 240. factor in any wear and tear loss, or any issues with the other MAF, and it all really makes sense.



you really need to know what it is putting down to the wheels. the rest is useless and only there to appease those who want to see big numbers.



also, to accurately measure increases, you need an eddy current dyno, that places a load on things. the fan used must also be able to create at least an 80mph "wind" at the front of the car, and the hood must be down for all tests.

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[netopyer]

what exactly is not accurate on graph posted above?



you can see WHP in blue, you can see MEASURED , NOT CALCULATED losses in green, and you can see final crank HP



measurment of power losses:

after you measure - rev it up on apropriate gear to maximum RPM, you press and hold clutch and let the car slow down to speed on which you started the dyno run .

during this slow-down period, losses are calculated very precisely so you can get crank HP..



this type of dyno is very often used by car manufacturers to provide official numbers.

if interested, you can find more information when typing MAHA LPS 3000 into google.....





just one more thing to add...:

we experienced various WHP result on the same car, same day, same hour, same setup ONLY by fastening the car more to the ground to avoid tire slip.

crank HP were always the same, because measured losses on more fastened car were bigger,

i really hope that you understand what i was trying to say all the time.....

i am no way saying that measuring WHP is not relevant...

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[flash]

no worries. all i am saying is that calculated figures are not relevant, and only what you are putting down to the ground is relevant. measured loss isn't even really relevant, as there are still variables at play. those need to be eliminated from the equation.



as an analogy of the extreme, it doesn't matter if you have 1000hp at the engine, if you can only apply 600 of it to the ground. the rest is just ego and bragging rights, but has no bearing on how fast the car is.



i understand how the measurement works. we do the same thing.



as for accuracy, unless that car is a 4wd car, there is no way i can see that there is 70hp of drivetrain loss. i've never seen anything 2wd, short of a big truck, have that kind of loss. most 2wd passenger cars are less than 45hp loss



do you have the chart showing the loss on the 968? i know what the cars we tested showed for loss, and it matches perfectly what others have shown to be the net of the OEM specced engine power less what they have shown at the wheels, thereby validating our measurements.

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[netopyer]

unfortunately not, but i will try to get it plotted on the graph. if not possible, i will try to get a plot needed from next dyno run (with cleaned injectors and replaced FPR + all vacuum lines)

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[jurek968]

Winter tyres can lower score by 5 % , You will not see it on the graf.Dyno computer do not see them to.

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