Originally posted by Jeff Taylor
hehe
Here's my logic...
Let's say you're comparing two 240sx drivetains... One has a stock engine that puts out 155 Hp, the other has a fully built engine that's putting out 500 Hp.
They both have the same exact transmission. Same gear oil in it, etc. However, when using the 15% loss factor, the transmission on the 155 Hp engine has a loss of only 23 Hp, while the transmission on the 500 Hp engine has a loss of 75 Hp.
So how is it possible for the same exact transmission to have different mechanical losses? 
...This is the reason I call percentage losses bullshit, and should only be used as a very poor rule-of-thumb.
Jeff
I'll have a go. In my very limited schooling, I was under the impression that mechanical losses are attributed to the mechanical efficiency of the system as a whole. As far as I know, mechanical efficiency is always expressed in a percentage, so drivetrain losses are expressed in a percentage.
Maybe I'll put into another example that I'm more familiar with. In computers, most processors or processing systems have an error rate. For instance, system memory normally has a maximum accepted error rate ( for this example, say 1 out of every million instructions causes an error). The more instructions you push through that device, the more errors occur, so the error rate is expressed as a percentage ( i.e. 1/1000000th ). I really haven't been working on or studying engines for long, so please correct me if I'm wrong. I'm just taking a stab at it.