Driveline losses
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Driveline losses
I didn't want to hijack the other thread about the Cobra, but Derek and I got to talking about drivetrain losses and how to calculate them.
There seem to be 2 schools of thought on this:
A) Driveline loss is a percentage of Hp, so the higher the Hp of the engine, the higher the driveline loss
B) Driveline loss is determined solely by the components in the driveline and is fixed, regardless of the Hp of the motor
I asked the question to some guys I know on an email list and below is their reasoning. Please note that both seem to fall under theory "A" (which I still need to see proof of because I'm a theory "B" kinda guy).
This guy below puts it into an easily understandable yet painful perspective. Still not sure I believe it, but it seems plausible.
So what do you guys think? Is driveline loss fixed or is it a percentage of Hp? Everyone please reply before Porsche Dude because he's going to be right and it won't matter after that 
There seem to be 2 schools of thought on this:
A) Driveline loss is a percentage of Hp, so the higher the Hp of the engine, the higher the driveline loss
B) Driveline loss is determined solely by the components in the driveline and is fixed, regardless of the Hp of the motor
I asked the question to some guys I know on an email list and below is their reasoning. Please note that both seem to fall under theory "A" (which I still need to see proof of because I'm a theory "B" kinda guy).
I'm no engineer, and I don't even try to claim I'm close to one, but here's my take on the situation. Parasitic drag increases proportionally (?) to speed/power. Quick example, get a T-5 transmission, put it in 3rd gear and spin the input shaft by hand. Spins pretty easy at first, and then the faster you try to spin it, the harder it gets because the resistance increases. Same with a rear end. The faster you try to spin it, the harder it gets. The "flat loss" idea is no good, because take that same T-5 and rear end and hook them up as a testbed. Now if that "drivetrain" had a flat HP loss of say, 40hp, then if I hooked up a 5hp Briggs & Stratton motor to it, it wouldn't turn? But I can turn it by hand, remember? That pretty much shoots the "flat loss" theory right in the ! ass. Now as for what percentage to go by, that will be debated forever as every component can change that so there will never be a single "correct" percentage.
Simple example - Take 80 grit sandpaper and rub it on your leg really slow.
Now ask The Rock to do it. More friction, more heat, more losses.
It's not a straight percentage, and it's not a one time block of 15 horses,
either. As you increase the power there are larger and larger losses, but
the percentage of loss is less and less compared to the total output as you
increase the power. Your returns (losses) are diminishing as you put more
power into it. This changes when you blow the tranny, and your losses (in
percentages) increase again.
Now ask The Rock to do it. More friction, more heat, more losses.
It's not a straight percentage, and it's not a one time block of 15 horses,
either. As you increase the power there are larger and larger losses, but
the percentage of loss is less and less compared to the total output as you
increase the power. Your returns (losses) are diminishing as you put more
power into it. This changes when you blow the tranny, and your losses (in
percentages) increase again.
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WRX guys in australia claim B.. and i beleive them.. just because you add more HP to the engine doesnt change the amount of HP that is needed to move the drive train...
you can certainly lessen the amount of effort needed to get the power to the ground.. and thus raise the amount that makes it..
you can certainly lessen the amount of effort needed to get the power to the ground.. and thus raise the amount that makes it..
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I go with a mix of A and B. Plus I found this thread from a simple google search. He's a mustang guy he must be right His explinations are very logical and easy to follow.
http://www.superstang.com/horsepower.htm
His explinations are very logical and easy to follow.http://www.superstang.com/horsepower.htm
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This sentence also well explains the losses of numerically higher gears on a dynojet. Which so many disputed as untrue.
The reported HP (flywheel -or- rear wheel), is highly dependent on acceleration rate. The higher the acceleration rate, the lower the reported HP. So on a dynojet-type dynamometer (fixed inertia), higher horsepower will accelerate the drum quicker, which will increase drivetrain inertial losses, thereby reporting even lower RWHP numbers
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The^Thief has hit the nail pretty well on the head, but here is another factor many people ignore in their concideration of drivetrain losses. Tires.
Tire distortion sucks up a good chunk of the energy we concider part of 'drivetrain losses'.
Just think about how hard it is to push your car across a smooth flat surface. You can't blame all that drag on the gears and lubrication in your tranny.
Tire distortion sucks up a good chunk of the energy we concider part of 'drivetrain losses'.
Just think about how hard it is to push your car across a smooth flat surface. You can't blame all that drag on the gears and lubrication in your tranny.
