Drivetrain Parasitic Loss
#16
03-20-2006, 10:06 AM
Just to make you guys feel better. Take a look at these chassis dyno numbers from a cross section of old and newish Pontiac muscle cars:
They speak of how tire size, diff ratio affects the outcome on dyno.
Look at thoses monster peak torques and relatively low HP for such big engines [ 389, 400, & 455] compared to a modern 346. Remember your engine is 214 cubic inches.
http://www.highperformancepontiac.co...407pon_engine/
They speak of how tire size, diff ratio affects the outcome on dyno.
Look at thoses monster peak torques and relatively low HP for such big engines [ 389, 400, & 455] compared to a modern 346. Remember your engine is 214 cubic inches.
http://www.highperformancepontiac.co...407pon_engine/
#17
03-20-2006, 10:29 AM
The problem with deriving a drivetrain loss percentage is that it's a moving target. One must take absolute endpoints to calculate the loss. We have one absolute endpoint, the published crank numbers, and the other endpoint, rear-wheel horsepower, is not so absolute. I'm preaching to the choir here, but every dyno we see posted is different, and comparisons amongst dynos should not be made lightly. Then one has the method MechEE describes.
For what it's worth, Doug Stewart, from Crawford, claims a 17% loss for manuals when comparing against his local dynojet numbers.
And I agree with Pasta that the numbers cannot be inflated. Our cars exhibit a relatively flat torque curve, and is a loss in the neighborhood of 25% or greater were in fact accurate, people would not be hitting 13's at over 100mph stock, especially in a 3500 pound car.
For what it's worth, Doug Stewart, from Crawford, claims a 17% loss for manuals when comparing against his local dynojet numbers.
And I agree with Pasta that the numbers cannot be inflated. Our cars exhibit a relatively flat torque curve, and is a loss in the neighborhood of 25% or greater were in fact accurate, people would not be hitting 13's at over 100mph stock, especially in a 3500 pound car.
#18
03-20-2006, 12:21 PM
http://swri.edu/4org/d03/vehsys/pres...ainTesting.pdf
Interesting graphs in middle for different components.
Simple to measure power losses by measuring the temperature rise of each component STEADY STATE LOSSES..........however more complicated in a short time of acceleration.
Things like torque convertors have variable losses depending on the speed difference input to output vs steady state of say 12-3-14% or 3% in lockup mode. They are also speed sensitive based on churning of ATF and amount of air bubbles created and absorbed by ATF. Same with the tranny pump efficiency it is speed sensitive over the 2,000- 7,000 rpm input range.
http://www.kennebell.net/techinfo/ge...tVariables.pdf
Interesting graphs in middle for different components.
Simple to measure power losses by measuring the temperature rise of each component STEADY STATE LOSSES..........however more complicated in a short time of acceleration.
Things like torque convertors have variable losses depending on the speed difference input to output vs steady state of say 12-3-14% or 3% in lockup mode. They are also speed sensitive based on churning of ATF and amount of air bubbles created and absorbed by ATF. Same with the tranny pump efficiency it is speed sensitive over the 2,000- 7,000 rpm input range.
http://www.kennebell.net/techinfo/ge...tVariables.pdf
#19
03-20-2006, 12:49 PM
#20
03-20-2006, 01:16 PM
I do wish I dyno'd my G stock.
I took the average of 220 WHP into account when I took my car to the dyno over last summer. It was 93 degrees, on a dynojet with the following mods: AEM CAI and Stillen dual exhaust. I got 231 WHP, so the mods gave me 11 WHP??! Now that I think about it, it might seem a bit high. Then 2 weeks ago I got the car dyno'd on a Mustang dyno with the same mods (in addition to Craford plenum/cats and IMR grounding kit) and got 238 WHP. So, that's a 7 WHP gain. If I believe the Mustang that is. Perhaps I should take the car back to the dynojet place and get it dyno'd there again in "non-Sahara" conditions.
I took the average of 220 WHP into account when I took my car to the dyno over last summer. It was 93 degrees, on a dynojet with the following mods: AEM CAI and Stillen dual exhaust. I got 231 WHP, so the mods gave me 11 WHP??! Now that I think about it, it might seem a bit high. Then 2 weeks ago I got the car dyno'd on a Mustang dyno with the same mods (in addition to Craford plenum/cats and IMR grounding kit) and got 238 WHP. So, that's a 7 WHP gain. If I believe the Mustang that is. Perhaps I should take the car back to the dynojet place and get it dyno'd there again in "non-Sahara" conditions.
#21
03-20-2006, 02:10 PM
FYI, you don't multiply the numbers times 1.X (X being the assumed % loss). The correct way to calculate the loss is divide the whp by 1-assumed % loss.
I think it's very safe to assume a 20% loss for an auto and around 17% for the 6MT. So here's the formula:
Auto making 231whp = 231/.8 = 289hp
6MT making 231whp = 231/.83 = 278hp
I think it's very safe to assume a 20% loss for an auto and around 17% for the 6MT. So here's the formula:
Auto making 231whp = 231/.8 = 289hp
6MT making 231whp = 231/.83 = 278hp
#22
03-20-2006, 05:18 PM
There is no single accurate number [accurate to 1% or even 2%] for losses it varies as you change rpm.
Losses at 4,000 will be less than losses at 6500. Losses will change during the dyno run as the [diff and tranny] lubricants heat up and as the tires change temperature.
This is in addition to the probable power losses from the engine as it heats up why back to back runs vary.
Losses at 4,000 will be less than losses at 6500. Losses will change during the dyno run as the [diff and tranny] lubricants heat up and as the tires change temperature.
This is in addition to the probable power losses from the engine as it heats up why back to back runs vary.
#23
03-20-2006, 06:59 PM
Originally Posted by trey.hutcheson
The problem with deriving a drivetrain loss percentage is that it's a moving target. One must take absolute endpoints to calculate the loss. We have one absolute endpoint, the published crank numbers, and the other endpoint, rear-wheel horsepower, is not so absolute. I'm preaching to the choir here, but every dyno we see posted is different, and comparisons amongst dynos should not be made lightly. Then one has the method MechEE describes.
For what it's worth, Doug Stewart, from Crawford, claims a 17% loss for manuals when comparing against his local dynojet numbers.
And I agree with Pasta that the numbers cannot be inflated. Our cars exhibit a relatively flat torque curve, and is a loss in the neighborhood of 25% or greater were in fact accurate, people would not be hitting 13's at over 100mph stock, especially in a 3500 pound car.
For what it's worth, Doug Stewart, from Crawford, claims a 17% loss for manuals when comparing against his local dynojet numbers.
And I agree with Pasta that the numbers cannot be inflated. Our cars exhibit a relatively flat torque curve, and is a loss in the neighborhood of 25% or greater were in fact accurate, people would not be hitting 13's at over 100mph stock, especially in a 3500 pound car.
What would be interesting is to simulate some 1/4 mile accelerations with a stock power curve, and scale it until you get trap speed numbers similar to what people are getting stock. This will give you a rough idea of how much power they are putting down, and would be pretty easy to simulate. Since I have high-resolution data from my dyno, I'll use mine, and scale it up or down to get various trap speeds.
#24
03-20-2006, 07:05 PM
Originally Posted by thx007
But...
"...if we agree that stock cars chassis dyno at 210-220, well 215 x 1.2 = 258 flywheel hp, a far cry from what Infiniti says (280 or 298)."
So 215 x 1.22 still only gives you 262. Perhaps a better question would be, was there a noticeable chassis dyno difference between the 03-04 cars and the 05's?
If a 298hp rated 6MT dyno's at 230rwhp, that's a huge 29.6% loss. I can't believe we are losing that much.
"...if we agree that stock cars chassis dyno at 210-220, well 215 x 1.2 = 258 flywheel hp, a far cry from what Infiniti says (280 or 298)."
So 215 x 1.22 still only gives you 262. Perhaps a better question would be, was there a noticeable chassis dyno difference between the 03-04 cars and the 05's?
If a 298hp rated 6MT dyno's at 230rwhp, that's a huge 29.6% loss. I can't believe we are losing that much.
The 22% loss applies to the HP at the crank not the HP at the wheels. So for a 22% loss the math should be like this:
For a 280hp (crank) motor 280 * 0.78 = 218.4 hp at the wheels
For a 298hp (crank) motor 298 * 0.78 = 232.44 hp at the wheels
From your exaple above of a 298hp engine with a dyno of 230 - that would convert to a 22.8% drivetrain loss (not 29.6)
An easier way to think of it is like this. If a motor makes 280hp but looses 22% of it to drivetrain it will lose 280 * 0.22 = 61.6hp. So if it looses 61.6 hp in the drivetrain you would expect the car to put down 280 - 61.6 = 218.4hp at the wheels.
#25
03-20-2006, 09:48 PM
Join Date: Dec 2005
Posts: 20
Likes: 0
Received 0 Likes
on
0 Posts
#26
03-20-2006, 11:52 PM
#27
03-20-2006, 11:52 PM
Originally Posted by MechEE
Again, it's hard to dispute the fact that I can measure quite accurately instantaneous acceleration and speed, which gives me power directly with the weight of the car.
What would be interesting is to simulate some 1/4 mile accelerations with a stock power curve, and scale it until you get trap speed numbers similar to what people are getting stock. This will give you a rough idea of how much power they are putting down, and would be pretty easy to simulate. Since I have high-resolution data from my dyno, I'll use mine, and scale it up or down to get various trap speeds.
What would be interesting is to simulate some 1/4 mile accelerations with a stock power curve, and scale it until you get trap speed numbers similar to what people are getting stock. This will give you a rough idea of how much power they are putting down, and would be pretty easy to simulate. Since I have high-resolution data from my dyno, I'll use mine, and scale it up or down to get various trap speeds.
#28
03-21-2006, 12:10 AM
Join Date: Dec 2005
Posts: 20
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by trey.hutcheson
That auto tranny ain't helping there...
Besides, we're catching up. The new 6AT C6 is only .2 off the 6MT version. Ok, ok... granted I don't have a lightweight, transaxle mounted, paddle-shifting tranny. But give me time!!
#30
03-21-2006, 11:23 PM
Originally Posted by thx007
Seems like the drivetrain should still be more efficient than that. It still makes it similiar to a heavy truck drivetrain in amount of loss.
I WANT MORE POWER TO THE GROUND!!!
I WANT MORE POWER TO THE GROUND!!!
As for drivetrain losses, consider some things. These cars have a big and heavy driveshaft to keep the drivetrain extremely smooth. The driveshaft has to spin two axles to move the car. These cars also have rather heavy rims and beefy (heavy) brakes. It all adds up. A FWD car with the same motor will see around 10whp more simply because it doesn't have a driveshaft.