Re: Drivetrain Efficiency

["Thomas Petersen" <bmw318is92@xxxxxxxxxxx>]

I've spend much time on the dyno, while getting my supercharger to work 
properly. I've also been thinking about that transmission loss. In my case 
we used 0.8 (e.g. 20% transmission loss). But the guy running the dyno told 
me that it was only a approximation, if you where to measure it, you'll find 
that it's not a constant meaning that the loss will increase with the wheel 
speed. So, that will also mean that the loss are not the same in every gear. 
If I remember correct, I think he told me that the loss was about 40% in 
5'th at max. speed.
Another thing, is that most of the loss is from the friction of the tires 
against the roller of the dyno.

Thomas Petersen
'92 318is Coupe - Supercharged to 205 HP.

>------------------------------
>
>Date: Tue, 5 Sep 2000 16:50:51 -0500
>From: "Michael Ting" <lupin@domain.elided>
>Subject: Drivetrain Efficiency
>
>I'm sure we're all familiar the terms HP@Crankshaft and HP@Wheel.
>
>When we measure HP using common Dyno machines, we are measuring the
>HP@Wheel. Then, using an approximation constant, we approximate the actual
>HP@Crank.
>
>I've never been into any Dyno shop, so correct me if I'm wrong. From what
>I've heard, HP@Wheel = .85 HP@Crank. (approximation) For automatic trans,
>it's more like HP@Wheel= .80 HP@Crank.
>
>The constant (.85, or .80) comes from the energy loss through the
>driveshaft(Is this the proper word to use??). Well, my question is do 
>people
>actually measure the different driveshaft efficiency on different cars??
>In another word, different cars should have different efficiency. Different
>set ups (Front wheel, Rear wheel, All wheel Drive), or different material
>used. (I heard either 944 or 928 has fiber reinforced aluminum shaft).
>
>So, maybe in a Ferrari, HP@Wheel = .9 HP@Crank. (You get the idea)
>
>Anybody wants to toss in their $.02?
>
>
>
>Michael Ting
>- --------------------
>

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