05-25-2012, 01:42 PM | #2017 | |
I just like V8s
Drives: 2007 Corvette Z06 Join Date: Mar 2007
Location: Stuttgart, Germany
Posts: 919
|
Quote:
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.
__________________
"Anyone know who sells the driver mods?"
2007 Corvette Z06: Le Mans blue, 2LZ |
|
05-25-2012, 01:42 PM | #2018 | |
Banned
Drives: '71 'Cuda, '87 GN, '13 Shelby GT500 Join Date: May 2012
Location: Michigan
Posts: 16
|
Quote:
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. Last edited by Barracuda; 05-25-2012 at 02:55 PM. |
|
05-25-2012, 01:49 PM | #2019 | |
Banned
Drives: 1968 Ford Galaxie Join Date: Mar 2010
Location: San Jose
Posts: 630
|
Quote:
|
|
05-25-2012, 01:51 PM | #2020 | |
Banned
Drives: various Join Date: Apr 2012
Location: Florida
Posts: 66
|
Quote:
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. |
|
05-25-2012, 01:51 PM | #2021 | |
Drives: 2023 ZLE Join Date: Jun 2009
Location: Detroit
Posts: 1,717
|
Quote:
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. |
|
05-25-2012, 01:52 PM | #2022 |
I just like V8s
Drives: 2007 Corvette Z06 Join Date: Mar 2007
Location: Stuttgart, Germany
Posts: 919
|
Nice post 'cuda.
__________________
"Anyone know who sells the driver mods?"
2007 Corvette Z06: Le Mans blue, 2LZ |
05-25-2012, 01:54 PM | #2023 | |
Drives: 2005 STi corn fed Join Date: Jul 2008
Location: Colorado
Posts: 2,997
|
Quote:
|
|
05-25-2012, 01:56 PM | #2024 | |
Drives: 2013 A6 GT 5.0 Join Date: Nov 2009
Location: Edmond, OK
Posts: 2,909
|
Quote:
__________________
BLK/BLK 1SS/RS Ordered 11-01-2009 Took delivery 12-22-2009. Heads/cam/converter/bolt ons. SOLD Feb 2015 to fund 6th gen LT1 SS with 8L90E.
|
|
05-25-2012, 01:57 PM | #2025 | ||
Drives: 2010 Camaro 2SS RS Join Date: Jan 2011
Location: Michigan
Posts: 60
|
Quote:
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. Quote:
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.
__________________
|
||
05-25-2012, 01:59 PM | #2026 | |
Banned
Drives: 2012 mustanng gt, 1968 chevy camaro Join Date: Apr 2012
Location: home
Posts: 115
|
Quote:
it will DEFINITELY hit high 11's "as delivered". but that's still kinda slow'ish in the realm of these cars. |
|
05-25-2012, 02:00 PM | #2027 | |
Drives: 2013 A6 GT 5.0 Join Date: Nov 2009
Location: Edmond, OK
Posts: 2,909
|
Quote:
__________________
BLK/BLK 1SS/RS Ordered 11-01-2009 Took delivery 12-22-2009. Heads/cam/converter/bolt ons. SOLD Feb 2015 to fund 6th gen LT1 SS with 8L90E.
|
|
05-25-2012, 02:04 PM | #2028 | ||
Banned
Drives: '71 'Cuda, '87 GN, '13 Shelby GT500 Join Date: May 2012
Location: Michigan
Posts: 16
|
Quote:
Quote:
Last edited by Barracuda; 05-25-2012 at 02:49 PM. |
||
05-25-2012, 02:04 PM | #2029 |
Drives: 2023 ZLE Join Date: Jun 2009
Location: Detroit
Posts: 1,717
|
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.
|
05-25-2012, 02:05 PM | #2030 |
Banned
Drives: various Join Date: Apr 2012
Location: Florida
Posts: 66
|
My grandfather used to say "now you're just picking fly shit out of the pepper"... I think we may be approaching that point...
|
Post Reply
|
|
|