? for the mechanical engineers
 

Just a quick question about drivetrain loss.......

So lets say you have a 240 hp (crank) S2000 that puts down 200 to the wheels and have about 17% drivetrain loss.

Ok, now you add forced induction and the WHP goes to 300. Is the drivetrain loss constant so you actually added 117 at the crank and have ~357? Or would the 40 hp lost to friction in the stock example be spread out over 340 for a lower percentage. Or is there still loss to the drivetrain but at a lesser percentage as you add more power?

I don't know the physics behind it.


Gracias.

i cant understand you,
but i hope this helps..
i was stock at 30 hp loosing from transfer from the flywheel to the wheels and now at 400 hp i still loose 30hp from the flywheel to the wheels.
so the same loss both thimes. no need to do a % calculation,
the loos in 4th gear is 30 hp and in 6th is 46hp.
stefce

The frictional loss according to the equations should stay as a % loss.

If you loose 17% at stock horsepower you should also loose about 17% at a higher horsepower.

Edited:

As GrandMasterKhan correctly pointed out the parasitic losses should stay the same HP number.

IMO it only takes so much power to move a part. For example if a/c robs the car of 24hp which is 10%

then your car has 2400 hp it doesnt take 240 hp to spin the a/c compressor.

*This is a rough hypothectially exaggerated example but it gets the point across*

If you add horsepower you will lose more through drivetrain loss. However, I also do not believe that it is a set percentage.

Ex. If a stock s2000 dyno's 204whp (a loss of 36hp or 15%), I do not think a 480bhp s2000 will dyno 408whp (A loss of 72hp or 15%). I think it will be less, somewhere around 430whp.

This is all IMO through research and numbers I have seen on the net.

Another example would be the vortech superchargers. They advertise that the ap1 system increases bhp by 118. Most ap1's will dyno about 215 whp (25hp or rougly 12% loss) on Church's dynapack. With a stock s2000 and the vortech they will do about 325 whp on the same dyno. If the number was exactly 12% it would be about 315whp. However, if it was just the 25hp loss it would be about 333whp. So yea it loses about another 8-10whp.

Side note, 12% loss can't be right for a stock S2K. I'm thinking 15% is right. C5 vettes have a more efficient drivetrain and they lose 13% from crank to wheels.

It's neither. It's not a percent and it's not a single number that's constant. There are a lot of sources of loss which are a bit too complicated for a single number to model. SCC did a detailed explanation a year or two ago (probably Dave Coleman). It may be floating around on the internet somewhere.

I would also suggest looking into SAE papers on the subject. (www.sae.org)

Tim

^^ Correct, its never a fixed amount.

If the car is supercharged, the drivetrain loss is INCREASED, as the motor now has to give some power to spin the blower.

As an example, the Mclaren SLR uses almost 100hp just to spin the blower.