[Rock36]

Originally Posted by VADER SS L99

I would totally agree that it is very hard if not impossible to calculate exact crank horsepower from RWHP once you start modding but I never said that you could.

On my paticular setup I dont know if I'm loosing 110 RWHP but I can tell you for a fact that its alot more than the 80RWHP.
There is no one on here that could make me believe that once you get to X amount of horse power that after that you are not loosing any more through the drivetrain.

I never said the engine HP would go up from a 1 piece carbon fiber vs a 2 piece steel driveshaft I said the drivetrain LOSS would be less thus showing RWHP gains.

How do you know this? Simply put your drive train didn't become significantly harder to spin/move now that you have more power...

Check out 8cd3gr0's post. He does a bit better at explaining what I was trying to.

Not saying you made any claims in particular. Just trying to provide examples for clairity.

[Barracuda]

Originally Posted by 69bossnine

Never... but the percent/ratio of driveline-loss is increasingly diluted as you add more power...

I don't know how to explain it, I just know that it's a physics thing, exponential math and such...

Imagine a team of horses pulling a big sled... You add a horse, and 100% of the horse's power is not being translated directly into the "work" factor of the physics equation. But it does lessen the load for the other horses and makes the work easier for all. The percentage of horse-power versus the effort it takes to make the sled move is reduced.

As the general consensus here has been, driveline losses are neither a fixed amount nor a fixed percentage, but do decrease as a percentage with increased engine power. I'll try to explain - to the best of my knowledge and ability....

Driveline losses are a VERY complicated thing, with numerous components and equations of physics coming into play. But, in general, the driveline losses can be broken down into inertial and frictional losses. I'll leave the equations out for now, but...

Inertial Losses - this is the power lost in accelerating the driveline components. Since chassis dynos are transient (i.e. accelerating), unlike steady state engine dynos that are used to certify the engine, inertia comes into play. Just like it takes torque to accelerate your car, it takes torque to accelerate the driveline components. Take the driveshaft for example... It has a rotational inertia based on it's diameter, mass, and design (i.e. solid vs. hollow). A car with a heavier, larger diameter, hollow crankshaft will have higher inertial losses (for this single component) than a car with a lighter, smaller diameter, solid driveshaft. The question here, though, is for the same car (with the same driveshaft) and different engine power levels (along with assumed higher torque levels), do the inertial losses change. The answer is YES. That is because the driveline components are accelerating at a different rate. The work done in accelerating a driveshaft from 0 RPM to max speed is the same. But Power = Work/Time. So to go from 0 RPM to max speed quicker, it takes more power. If you measured RWH with a constant acceleration dyno, then the inertial losses would be the same regardless of engine HP. Otherwise, if the dyno accelerates quicker with higher engine HP (which the ones I know of do), you will see higher driveline losses from driveline inertia.

So, while these inertial losses are not a fixed value with varying engine HP, are they a fixed percentage? Not likely. The acceleration will not double with double the horsepower. It will depend more on torque and frictional losses (which also change - see below) than on engine HP. So the net effect will be an increased amount, but reduced percentage as engine HP increases. (NOTE: I realize Torque will increase the same percentage as HP if you assume the same peak HP engine speed. I did not make that assumption.)

Friction - Some elements of driveline friction will increase with increased engine power (i.e. torque). Others will not. To keep it simple, lets think of the gearbox. There is a certain amount of frictional losses related to the gears turning in oil. The magnitude of these losses are dependent upon oil type, viscosity, temperature, level of fill, rotational velocity, etc.. It is not affected by engine power (or torque). The force required to accelerate the gears through the oil may be affected with different levels of acceleration (as in the inertia description above), but there is a component of friction that will be unaffected by engine power. The friction due to gears meshing, on the other hand, will be affected by engine output. As you put more torque through the driveline, the contact force between meshing gears will increase, which increases the friction.

So, as some elements of friction go up with engine power (and torque) and other do not, then it is clear that this component of driveline losses is neither a fixed value nor percentage.

Hope this helps.

[MauriSSio]

Originally Posted by Barracuda

As the general consensus here has been, driveline losses are neither a fixed amount nor a fixed percentage, but do decrease as a percentage with increased engine power. I'll try to explain - to the best of my knowledge and ability....

Driveline losses are a VERY complicated thing, with numerous components and equations of physics coming into play. But, in general, the driveline losses can be broken down into inertial and frictional losses. I'll leave the equations out for now, but...

Inertial Losses - this is the power lost in accelerating the driveline components. Since chassis dynos are transient (i.e. accelerating), unlike steady state engine dynos that are used to certify the engine, inertia comes into play. Just like it takes torque to accelerate your car, it takes torque to accelerate the driveline components. Take the driveshaft for example... It has a rotational inertia based on it's diameter, mass, and design (i.e. solid vs. hollow). A car with a heavier, larger diameter, hollow crankshaft will have higher inertial losses (for this single component) than a car with a lighter, smaller diameter, solid driveshaft. The question here, though, is for the same car (with the same driveshaft) and different engine power levels (along with assumed higher torque levels), do the inertial losses change. The answer is YES. That is because the driveline components are accelerating at a different rate. The work done in accelerating a driveshaft from 0 RPM to max speed is the same. But Power = Work/Time. So to go from 0 RPM to max speed quicker, it takes more power. If you measured RWH with a constant acceleration dyno, then the inertial losses would be the same regardless of engine HP. Otherwise, if the dyno accelerates quicker with higher engine HP (which the ones I know of do), you will see higher driveline losses from driveline inertia.

So, while these inertial losses are not a fixed value with varying engine HP, are they a fixed percentage? Not likely. The acceleration will not double with double the horsepower. It will depend more on torque and frictional losses (which also change - see below) than on engine HP. So the net effect will be an increased amount, but reduced percentage as engine HP increases. (NOTE: I realize Torque will increase the same percentage as HP if you assume the same peak HP engine speed. I did not make that assumption.)

Friction - Some elements of driveline friction will increase with increased engine power (i.e. torque). Others will not. To keep it simple, lets think of the gearbox. There is a certain amount of frictional losses related to the gears turning in oil. The magnitude of these losses are dependent upon oil type, viscosity, temperature, level of fill, rotational velocity, etc.. It is not affected by engine power (or torque). The force required to accelerate the gears through the oil may be affected with different levels of acceleration (as in the inertia description above), but there is a component of friction that will be unaffected by engine power. The friction due to gears meshing, on the other hand, will be affected by engine output. As you put more torque through the driveline, the contact force between meshing gears will increase, which increases the friction.

So, as some elements of friction go up with engine power (and torque) and other do not, then it is clear that this component of driveline losses is neither a fixed value or percentage.

Hope this helps.

thanks, thats pretty much what i thought it was. Losses go up, but as a percent it goes down a bit.

[69bossnine]

Originally Posted by Barracuda

As the general consensus here has been, driveline losses are neither a fixed amount nor a fixed percentage, but do decrease as a percentage with increased engine power. I'll try to explain - to the best of my knowledge and ability....

Driveline losses are a VERY complicated thing, with numerous components and equations of physics coming into play. But, in general, the driveline losses can be broken down into inertial and frictional losses. I'll leave the equations out for now, but...

Inertial Losses - this is the power lost in accelerating the driveline components. Since chassis dynos are transient (i.e. accelerating), unlike steady state engine dynos that are used to certify the engine, inertia comes into play. Just like it takes torque to accelerate your car, it takes torque to accelerate the driveline components. Take the driveshaft for example... It has a rotational inertia based on it's diameter, mass, and design (i.e. solid vs. hollow). A car with a heavier, larger diameter, hollow crankshaft will have higher inertial losses (for this single component) than a car with a lighter, smaller diameter, solid driveshaft. The question here, though, is for the same car (with the same driveshaft) and different engine power levels (along with assumed higher torque levels), do the inertial losses change. The answer is YES. That is because the driveline components are accelerating at a different rate. The work done in accelerating a driveshaft from 0 RPM to max speed is the same. But Power = Work/Time. So to go from 0 RPM to max speed quicker, it takes more power. If you measured RWH with a constant acceleration dyno, then the inertial losses would be the same regardless of engine HP. Otherwise, if the dyno accelerates quicker with higher engine HP (which the ones I know of do), you will see higher driveline losses from driveline inertia.

So, while these inertial losses are not a fixed value with varying engine HP, are they a fixed percentage? Not likely. The acceleration will not double with double the horsepower. It will depend more on torque and frictional losses (which also change - see below) than on engine HP. So the net effect will be an increased amount, but reduced percentage as engine HP increases. (NOTE: I realize Torque will increase the same percentage as HP if you assume the same peak HP engine speed. I did not make that assumption.)

Friction - Some elements of driveline friction will increase with increased engine power (i.e. torque). Others will not. To keep it simple, lets think of the gearbox. There is a certain amount of frictional losses related to the gears turning in oil. The magnitude of these losses are dependent upon oil type, viscosity, temperature, level of fill, rotational velocity, etc.. It is not affected by engine power (or torque). The force required to accelerate the gears through the oil may be affected with different levels of acceleration (as in the inertia description above), but there is a component of friction that will be unaffected by engine power. The friction due to gears meshing, on the other hand, will be affected by engine output. As you put more torque through the driveline, the contact force between meshing gears will increase, which increases the friction.

So, as some elements of friction go up with engine power (and torque) and other do not, then it is clear that this component of driveline losses is neither a fixed value or percentage.

Hope this helps.

THANKS!! I think that means I was correct, I just lacked the eloquence (and the engineering degree) to communicate it, right?

Vader SS, you're kinda trying to apply 2-dimensional 2+2=4 math to a 3-dimensional complex physics-equation. And I mean that in a tryin' to help you out way, not in a condescending way.

[Blueclyde]

Originally Posted by 8cd03gro

Loss to heat as a percentage of power output decreases as power increases because inertia of the drivetrain and friction remain the same regardless of power output. This does not mean loss is a constant because some forces are variable, but the impact of constant forces become less apparent as power increases. These are just hypothetical and in no way accurate as it leaves out a loooottt of variables, but as an example

Let's say I is the force required to overcome the inertia of the drivetrain, it is a constant. Y is the total power output of the engine and X is the power at the wheels. Just for simplicity we will assume a 12% loss due to variables other than inertia. In this oversimplified example the function of total power output to determine wheel hp would be

X = 0.88Y-I

As Y increases, I remains the same. So, let's say I is 10hp, and Y is 400hp.

X = 0.88(400)-10
X = 342 or 85.5% of crank horsepower.

Now we'll increase crank output to 500

X = 0.88(500)-10
X = 430 or 86% of crank horsepower.

Now, again this is massively oversimplified, but you get the idea. Some of the factors that drain hp are constant and some are variable. As you increase power, the constants have less of an impact as far as percentage loss is concerned.

Any engineers, feel free to correct me. My expertise lies in econometrics, not engineering.

I think your general premise here is correct. It is somewhat simplified but I think sound in principle.

We are also forgetting about the dynos themselves. There is a lot that goes into maintaining and operating a dyno properly. I have little experience with chassis dynos but am involved with a lot of engine testing on engine dynos. Who is to say these chassis dynos are even properly maintained and calibrated. There are so many variables with these chassis dynos. I am very skeptical of them. They are only good for delta comparisons.

The only numbers I really believe are the crankshaft power numbers that come from Ford and GM, in terms of these two cars. Those numbers are correct.

[Rock36]

Nice post 'cuda.

[8cd03gro]

Originally Posted by Blueclyde

I think you general premise here is correct. It is somewhat simplified but I think sound in principle.

We are also forgetting about the dynos themselves. There is a lot that goes into maintaining and operating a dyno properly. I have little experience with chassis dynos but am involved with a lot of engine testing on engine dynos. Who is to say these chassis dynos are even properly maintained and calibrated. There are so many variables with these chassis dynos. I am very skeptical of them. They are only good for delta comparisons.

The only numbers I really believe are the crankshaft power numbers that come from Ford and GM, in terms of these two cars. Those numbers are correct.

Yes, a chassis dyno is a tuning tool, nothing more. I suspect the method for measuring output used by a dyno becomes increasingly imprecise as power increases as well, but I'm unsure. And again, my example is largely oversimplified and only serves to better explain the principle idea.

[VADER SS L99]

Originally Posted by Rock36

How do you know this? Simply put your drive train didn't become significantly harder to spin/move now that you have more power...

Check out 8cd3gr0's post. He does a bit better at explaining what I was trying to.

Not saying you made any claims in particular. Just trying to provide examples for clairity.

It may not have become significantly harder to spin/move the drivetrain parts but I can tell you for certain because I have a bit of experience with this that the driveline will eat up more than just x amount ( in your example 80RWHP). You don't get to a certain power level and then all of a sudden poof magic happens and there are no more drivetrain % losses because you have already used x amount of power( your example being 80RWHP.)

[ChuckD]

Originally Posted by MauriSSio

it might or might not be 662hp at the crank but we know its a legit 600+rwhp car. ZR1's only typically dyno 530-540rwhp so the GT500 is extremely efficient at putting it down to the wheels it seems

There's no question about it. At standard atmospheric conditions, that egnine makes 662 hp. That's it. No if's, and's, or buts.

It was measured according to the requirements of the SAE standard procedure. And SAE certification requires a third party witness to be present to acknowledge that proper protocol was followed and that the numbers are accurate. No further proof is needed.

Originally Posted by VADER SS L99

I think some of the reason for this is the 1 piece carbon fiber driveshaft which is a great idea btw. Its drivetrain loss probably truely is under 15%.

The carbon driveshaft is not for efficiency. It's to keep mass down and to keep rotational inertia low so that you can safely run at high speeds (200 mph).

Any time you increase the torque output of an engine, drivetrain mass creeps higher and higher in order to handle that torque. Carbon fiber shafts help to mitigate mass creep.

[1ltcap]

Originally Posted by tooslow

This, or at least on a very favorable weather day in an area of the country where median temps are not high and humidity is relatively low.

Is there really anyone who does not believe the ZL1 will hit high 11's on the factory Goodyears? I don't recall very many, if any, people disputing that probability, even the die-hard Mustang guys.

it will DEFINITELY hit high 11's "as delivered". but that's still kinda slow'ish in the realm of these cars.

[VADER SS L99]

Originally Posted by ChuckD

There's no question about it. At standard atmospheric conditions, that egnine makes 662 hp. That's it. No if's, and's, or buts.

It was measured according to the requirements of the SAE standard procedure. And SAE certification requires a third party witness to be present to acknowledge that proper protocol was followed and that the numbers are accurate. No further proof is needed.



The carbon driveshaft is not for efficiency. It's to keep mass down and to keep rotational inertia low so that you can safely run at high speeds (200 mph).

Any time you increase the torque output of an engine, drivetrain mass creeps higher and higher in order to handle that torque. Carbon fiber shafts help to mitigate mass creep.

You might be right but guess what? the byproduct is that with that paticular driveshaft that car WILL dyno higher #'s then with the old 2 piece steel shaft.

[Barracuda]

Originally Posted by 8cd03gro

Loss to heat as a percentage of power output decreases as power increases because inertia of the drivetrain and friction remain the same regardless of power output.

Heat is a result of friction. Friction does not remain the same regardless of power output (see my previous post), but does go down as a percentage as power increases. So loss to heat as a percentage does go down, but not due to inertia and not because friction stays the same.

Originally Posted by 8cd03gro

Let's say I is the force required to overcome the inertia of the drivetrain, it is a constant. Y is the total power output of the engine and X is the power at the wheels. Just for simplicity we will assume a 12% loss due to variables other than inertia. In this oversimplified example the function of total power output to determine wheel hp would be

X = 0.88Y-I

As Y increases, I remains the same. So, let's say I is 10hp, and Y is 400hp.

I is not measured in HP. I (inertia) for driveline purposes is the equivalent of a rotational mass. And like any mass (in the absence of friction or other external forces), it doesn't take any force to keep it moving at a constant speed. But it does take force (or torque for rotational purposes) to accelerate. If you want to know what it takes to accelerate a given rotational inertia to a given speed (i.e. RPM), then that is measured in work. How quickly you increase that inertia to that rotational speed (i.e. acceleration) can be measured in power (i.e. HP)

[Blueclyde]

Originally Posted by 1ltcap

it will DEFINITELY hit high 11's "as delivered". but that's still kinda slow'ish in the realm of these cars.

Forget the make of the car. When did a car capable of high 11's in factory trim become "slow'ish"? Not too many 11 second factory cars out there for this kind of money.

[69bossnine]

My grandfather used to say "now you're just picking fly shit out of the pepper"... I think we may be approaching that point...