HP losses from flywheel to wheels - Linear?

[RomanV]

I often hear people say that xxxx car loses 20% of its power through transmission, etc. etc.

But this doesnt seem to make sense to me.

I mean if the car had no engine, and you tried to turn the transmission by hand (assuming the wheels were off the ground) It would take a certain amount of torque to be applied before anything even moved.

So it seems strange to think that transmission losses could be expressed as a percentage, I would have thought it would be a fixed amount.

eg. to turn XXXX transmission at 3000RPM, takes 30 ft/lbs of torque.

To turn the same transmission at 5000RPM takes 50 ft/lbs of torque.

So if your engine made 100 ft/lbs of torque at 5000RPM, it would be 50% transmission loss.
If you made 500 ft/lbs of torque, you would only have 10% transmission loss.

Its not as if it takes more work to turn these parts if you have more power?

[trdfxgt]

im not one hundred percent sure but does the wieght of the car and the drag of the tires come into it as well

[fivebob]

http://www.pumaracing.co.uk/power3.htm
http://www.pumaracing.co.uk/coastdwn.htm
http://www.pumaracing.co.uk/setup01.htm

Actually most of what he says makes sense to me so read a few more from http://www.pumaracing.co.uk/mainmenu.htm

[RomanV]

Once again, Fivebob saves the day.

Cheers.

[strx7]

ahh yes back to this again, it comes up on every forum sooner or later.

The only way you can specifically say your particular car looses X HP thru the drivetrain is to hook an ENGINE DYNO upto your hub and dyno it. WTF would you want to do that you say? Cause all 'rolling road' dyno's measure the same power differently.

"JUDGE", the guy in aussie with e Giacatollo (sp?) who died at eastern creek a couple of years back, did back to back dyno runs on Dyno Jet, Dyno Dynamics and Dyna pac 'rolling road' type dyno's. the results he got showed the Dyno Pac recorded 9% less Hp that at the flywheel. the Dyno Jey recorded 15% less and the Dyno Dynamics recorded 27% less than flywheel. The engine in the car, cant recall exactly what it was, come kinda V8 in a comodore or similar had been engine dyno'd at somewhere between 300 and 450HP before being put into the car.

[vvega]

its simpe you wany bhp you use a engine dyno on your engine
you want rwhp you use a chassis dyno

you cannot get bhp off a rolling road or chassis dyno
bhp can only be got off a engine dyno

to be honest every trasmission is different
some logarithmic more some are linier some lose a base amount and then lose no more
this is where estamites all turn to shit

v

[fivebob]

The only way you can specifically say your particular car looses X HP thru the drivetrain is to hook an ENGINE DYNO upto your hub and dyno it.

Still got gearbox/diff losses to take into account, gets rid of the tyre slip though.

"JUDGE", the guy in aussie with e Giacatollo (sp?) who died at eastern creek a couple of years back, did back to back dyno runs on Dyno Jet, Dyno Dynamics and Dyna pac 'rolling road' type dyno's.

WTF , Dynapack doesn't make a rolling road dyno for cars, they're all hub dynos, which is what you describe above

[strx7]

There 'hub' dyno is still a 'rolling road' type of dyno as in its not an engine dyno. But it does explain, to a degree why that dyno has the least power reading difference.

If you hook an engine dyno upto the car's drive hub, its driving the power thru the gearbox/diff IS IT NOT???????