Since there is new info to add which addresses the theory above.

Well, the first dyno tests are coming in on the ZR1 in stock factory form. Looks like the drivetrain loss is 14% ~ 16% ... call it 15%.

No surprise there ... and goes to show that the 15% "rule of thumb" still holds true for a manual transmission Vette from 385 fwhp (2001 Z06) to 638 fwhp (2009 ZR1).

http://forums.corvetteforum.com/show....php?t=2137641

Also ...
http://www.autoblog.com/2008/09/24/c...d-at-535-rwhp/

 

 

I work with electric motors and associated equipment in industrial environments. Gear boxes are provided with efficiency as a percentage such as 98%. Gear boxes also often have a mechanical limit and a thermal limit. In other words, just because tranferring 500hp through a gear box won't break a part inside it does not mean you can do it, because it will overheat. If the losses were a fixed number then neither the efficiency as a percentage or the thermal rating would be correct. It seems to be a very large industry full of smart people so I can't see them all making mistakes like that.

It's not as simple as saying the loss of your car in 4th gear is 15% though. The loss will vary as the HP being transmitted through the drivetrain changes. It might be 12% when cruising and 18% when under full power. The percentage loss will never go down as the HP goes up though.

Between the engine and the wheels is basically a couple of gear boxes. Looking at industrial gearbox data is definately a valid comparism.

Peter

 

Sounds good , although i have no idea lol

 

When you have your HP in a relatively small window, then the % is probably close because the variation between cars is relatively small. But that constant can't be assumed to be true across the entire spectrum. I think it ends up offending people because they can't flex their e-muscles about how much HP their car makes since in reality its nowhere near what they think it is.

Its much like the guys who tell me their vintage muscle cars could run 180+ mph. When you ask them how they determined this they tell you that they buried the speedo at 120 and the car was still pulling...

But, let me give you an example of where this starts to spread.

There was a fellow I had a discussing with on another forum who posted up his RHP dyno graphs on a car making 800 RWHP and then claimed the car was at over 1000 crank HP. His basis for this claim was strictly made on the assumption of a fixed percentage. On his forum however they are using 20% for their percentage for a manual transmission car.

I've made the point before that I can bolt a car on the dyno and I know for a fact I can swing the dyno numbers 5% by changing parts in the driveline like wheels and tires. When you bring that point up people just want to dismiss it. But, go do the test for yourself. Go take a C5 Z06 with stock wheels and dyno it. Go put some of the really heavy chrome repro wheels on the car and re-dyno the car. Record your findings... Where did the 7-10HP go? How is it a fixed percentage if driveline mass has such a drastic effect?

All I am saying is if you want to use 15% as a "rule of thumb", then fine by all means go ahead. But, just be aware of the fact that depending on overall driveline mass that figure is subject to change...

 

No, it's not constant. It could vary like this for one particular vehicle;
10hp - 12%
100hp - 14%
1000hp - 15%

Note that the percentage will never go down as the HP goes up. You seem to imply the efficiency gets better as the power level goes up.


It sure is. There is no way to know what it is without measuring it.

Peter

 

that makes sense...i actually like telling others my horsepower at the crank...you'd be surprised how little ppl (if at all) know the difference between rw and crank horsepower