Wheel and Flywheel Torque

[rweir]

Question, I know that with 4wd cars there is about a 23% loss of power through the drivetrain to the wheels.

Is this the same for torque, or would I be right in saying this is not affected ?

[harperboy]

Doesn't that totaly depend on what you are measuring power in, as you can measure power in torque cant you? Or by power do you mean bhp?

[rweir]

Doesn't that totaly depend on what you are measuring power in, as you can measure power in torque cant you? Or by power do you mean bhp?

Well, for example, I have some figures which are is for power?! at wheels.

BHP: 376
Torque: 448

So, if I do the calcs and assume 23% "power" loss, I get lets say around 450 BHP, I assume the torque stays the same?

[DavidT]

Same losses for bhp and torque I think, 26% or 75 bhp losses for Torsen Quattro are good estimates.

[GrahamS4]

I'm no authority on this (can't even claim to fully follow it), but repeating what I have read elsewhere, a dyno does not meaure BHP it can only measure torque, the BHP being calculated from the measured torque.

I have never heard of people talking about looses and torque. Until convinced otherwise, I think torque is measured and does not differ from flywheel to wheels.

[JonnyX]

OK, the power loss through the drive train is pretty much an absolute figure
rather than a percentage (if we are talking about losses between the flywheel
and the road). I hate the use of percentages on modified cars (unless you
are expressing the difference between the measured crank power and the measured
wheel power as a percentage ).

Torque is a force (well, technically it's a moment a of force).
Power is the amount of work done in a specified time interval.

Again, to simplify, the power of the engine is the amount of torque it outputs
over a certain time period. This is normally expressed:

Engine RPM/5250 * torque = power. (on your dyno plots torque and power should
cross/touch at 5250 RPM)

disclaimer: I am using 5250 from memory, it may be wrong.

For arguments sake, if a standard car makes 200bhp@crank and loses 40bhp through
the transmission this represents a transmission loss of 20%. If the same car
is tuned to 400bhp and the same 20% loss figure used it now loses 80bhp through
the transmission. This is 40bhp, or ~30KW, of addtional power loss. Where did
we lose this extra power? The tranmission components are identical! (most
tranmission loss is power loss in accelerating rotating components). There will
be a slight increase in losses as you exert more load on components, more hysteresis
and therefore more heat. Not 30KW worth though.

Personally, I think wheel figures are fine

[GrahamS4]

Engine RPM/5250 * torque = power. (on your dyno plots torque and power should
cross/touch at 5250 RPM)

Mine cross at 5200rpm bang on.

[viperbl]

So,

After looking at BRETTCOLLINS post here I see he has two dyno runs, wheel and flywheel.

From what I can see, the torque and HP go when the flywheel dyno run is done. So, would this mean my flywheel torque should go up? Mine

[JonnyX]

So,

After looking at BRETTCOLLINS post here I see he has two dyno runs, wheel and flywheel.

From what I can see, the torque and HP go when the flywheel dyno run is done. So, would this mean my flywheel torque should go up? Mine

Unless the flywheel figure was measured on a bench dyno it's
a calculated figure. You can calculate how much energy is
stored in the rotation of the driveline components by doing
a coast down run and knowing what the load resistance is of
the RR's rollers. You can then use this to calculate power at
the flywheel.