[Z06] flywheel hp to rearwheel hp
06-30-2007, 11:24 PM
#2
Melting Slicks
Per the post below - approx. 12% driveline loss from crank to wheels
http://forums.corvetteforum.com/show....php?t=1726693
Divide rwhp by .88 or so to get crank hp.
Multiply crank hp x .88 to get rwhp.
http://forums.corvetteforum.com/show....php?t=1726693
Divide rwhp by .88 or so to get crank hp.
Multiply crank hp x .88 to get rwhp.
Last edited by HIRISC; 07-01-2007 at 12:05 AM.
07-01-2007, 12:59 AM
#3
There is no formula. It can range between 10-25% depending upon the car, and the specs of the drivetrain components. If you're asking about the Z06 or C6 in particular, it is usually on the low end of the range.
07-01-2007, 10:48 AM
#6
Race Director
plus, the more powerful the car, the greater the centrifugal losses, so even if you could average 10 Z06's on a rearwheel, as you add more power, the losses would become a greater percentage.
07-01-2007, 11:15 AM
#7
Safety Car
07-01-2007, 11:37 AM
#8
Le Mans Master
Actually it’s the other way around and the percentage factor doesn’t seem to apply accurately. It’s very close to a fixed value depending on drive train. The Z motors leave factory at 505 to 508 and the dyno’s have been running anywhere from 435 to 450 and even a bit higher from some. Katech told be that the Z's are in the single digit range if percentage is used. The frictional losses usually attributed to the percentage factor get screwed with lubrication elements.
07-01-2007, 11:52 AM
#9
Melting Slicks
Actually it’s the other way around and the percentage factor doesn’t seem to apply accurately. It’s very close to a fixed value depending on drive train. The Z motors leave factory at 505 to 508 and the dyno’s have been running anywhere from 435 to 450 and even a bit higher from some. Katech told be that the Z's are in the single digit range if percentage is used. The frictional losses usually attributed to the percentage factor get screwed with lubrication elements.
eg: 505*.88 = 444
444/.88 = 505
or +/- 12%
IMO, using 18% driveline loss on a (2wd) manual ______ car won't be very accurate.
07-01-2007, 03:29 PM
#10
Le Mans Master
You can use it as a reference if you wish but if you increase you engine performance you will not see a 12% factor with the new engine hp. In other words you can use the 505 - 444 = 61 hp loss and it will stay nearly that loss if you increase your engine hp by lets say 50 you will see 494 not 488.
07-01-2007, 03:33 PM
#11
If you want RWHP, just put it on a chassis dyno.
If you're talking about FWHP from RWHP, some of it depends on the type of dyno used. A Mustang dyno can put a load on a car and control the rate of engine acceleration (250 RPM/sec, 500 RPM/sec or whatever) or it can hold the RPM constant. That way, HP loss due to the inertia of engine components, drivetrain components and wheels/tires/rotors are held constant. On a Dynojet dyno, there is only the inertia of the drum to resist the torque at the wheels so when we add more HP or dyno in a lower gear, the time for the dyno run is less which means more HP loss to inertia.
Drivetrain HP loss on a chassis dyno is composed of the following:
1) second order or exponential losses like friction
2) first order or linear losses like inertia and gears
3) constants like windage of gears through the oil in the transmission/differential, shafts rotating through seals, and sidewall flex all at a particular RPM. In other words, those losses are independent of HP transmitted.
That leaves us with the equation HP (loss)= ax^2+bx+c where a, b, and c are constants and x is FWHP. "c" is the predominate term meaning most of the HP loss is a constant.
Other variables to consider is when a dyno run is done in a lower gear, the tire, transmission shafts/gears, and differential shafts/gears RPM is less reducing the HP loss to sidewall flex/windage and giving more RWHP. On a Dynojet, this is countered by a shorter dyno run increasing loss to inertia, not a factor on a Mustang dyno though since it keeps the time of the dyno run constant. Conversely, a dyno run in 5th or 6th on a Dynojet will have less loss to inertia (longer dyno run time) but more loss to windage/tires...but there's also a speed limitation on chassis dynos which prevents a run in 6th (unless you have some 4.56s in the rear). On the road, quicker acceleration in the lower gears results in more loss (as a percentage) to inertia, the same effect as a Dynojet.
As far as the 1:1 ratio of 4th gear being the best to dyno in, there is fact as a basis to that statement. Quality involute gears have a HP loss of ~1%, so when we dyno in 1st, 2nd, 3rd, 5th, or 6th, part of the drivetrain loss is ~2% of the HP transmitted through any of those gears (it's 2% because power flows through one set of gears from the input shaft to the countershaft then through another set of gears from the countershaft to the output shaft). You may notice the distinct absence of 4th gear in the list above...that's because there are no "gears" for 4th gear, something a lot of people don't know. When you make the shift to 4th gear, the synchro mechanism mechanically couples/locks the input shaft to the output shaft and power flows straight through the transmission making 4th gear the most efficient "gear" to dyno a car in as far as the transmission is concerned. It doesn't have anything to do with the fact the "ratio" is 1:1 since we could also put the power through gears at a 1:1 ratio and achieve the same output RPM.
Hopefully this shines a little light on the subject, it's neither a percentage or a constant. But if you had to pick one, you'll be closer to FWHP if you use a constant. I.E. if you dyno a stock Z06 and come up with 450 RWHP for a 55 HP/10.9% loss, then mod it to 600 RWHP on the same dyno, you'll be much closer to the true FWHP if you add the 55 HP loss from stock rather than back calculate using the percentage number. And the guys mod their cars to 600+RWHP that just pull a percentage number out of their *** (like 15%) to back calculate their FWHP are just looking to stroke their ego with a big number and impress people. The only way to know the percentage is to remove the engine and put it on an engine dyno to get the FWHP. But then the first time you mod the engine, that number is not valid anymore. The bottom line: there isn't a formula to calculate FWHP from RWHP...too many unknowns and too many variables, but it won't stop people from making up something.
If you're talking about FWHP from RWHP, some of it depends on the type of dyno used. A Mustang dyno can put a load on a car and control the rate of engine acceleration (250 RPM/sec, 500 RPM/sec or whatever) or it can hold the RPM constant. That way, HP loss due to the inertia of engine components, drivetrain components and wheels/tires/rotors are held constant. On a Dynojet dyno, there is only the inertia of the drum to resist the torque at the wheels so when we add more HP or dyno in a lower gear, the time for the dyno run is less which means more HP loss to inertia.
Drivetrain HP loss on a chassis dyno is composed of the following:
1) second order or exponential losses like friction
2) first order or linear losses like inertia and gears
3) constants like windage of gears through the oil in the transmission/differential, shafts rotating through seals, and sidewall flex all at a particular RPM. In other words, those losses are independent of HP transmitted.
That leaves us with the equation HP (loss)= ax^2+bx+c where a, b, and c are constants and x is FWHP. "c" is the predominate term meaning most of the HP loss is a constant.
Other variables to consider is when a dyno run is done in a lower gear, the tire, transmission shafts/gears, and differential shafts/gears RPM is less reducing the HP loss to sidewall flex/windage and giving more RWHP. On a Dynojet, this is countered by a shorter dyno run increasing loss to inertia, not a factor on a Mustang dyno though since it keeps the time of the dyno run constant. Conversely, a dyno run in 5th or 6th on a Dynojet will have less loss to inertia (longer dyno run time) but more loss to windage/tires...but there's also a speed limitation on chassis dynos which prevents a run in 6th (unless you have some 4.56s in the rear). On the road, quicker acceleration in the lower gears results in more loss (as a percentage) to inertia, the same effect as a Dynojet.
As far as the 1:1 ratio of 4th gear being the best to dyno in, there is fact as a basis to that statement. Quality involute gears have a HP loss of ~1%, so when we dyno in 1st, 2nd, 3rd, 5th, or 6th, part of the drivetrain loss is ~2% of the HP transmitted through any of those gears (it's 2% because power flows through one set of gears from the input shaft to the countershaft then through another set of gears from the countershaft to the output shaft). You may notice the distinct absence of 4th gear in the list above...that's because there are no "gears" for 4th gear, something a lot of people don't know. When you make the shift to 4th gear, the synchro mechanism mechanically couples/locks the input shaft to the output shaft and power flows straight through the transmission making 4th gear the most efficient "gear" to dyno a car in as far as the transmission is concerned. It doesn't have anything to do with the fact the "ratio" is 1:1 since we could also put the power through gears at a 1:1 ratio and achieve the same output RPM.
Hopefully this shines a little light on the subject, it's neither a percentage or a constant. But if you had to pick one, you'll be closer to FWHP if you use a constant. I.E. if you dyno a stock Z06 and come up with 450 RWHP for a 55 HP/10.9% loss, then mod it to 600 RWHP on the same dyno, you'll be much closer to the true FWHP if you add the 55 HP loss from stock rather than back calculate using the percentage number. And the guys mod their cars to 600+RWHP that just pull a percentage number out of their *** (like 15%) to back calculate their FWHP are just looking to stroke their ego with a big number and impress people. The only way to know the percentage is to remove the engine and put it on an engine dyno to get the FWHP. But then the first time you mod the engine, that number is not valid anymore. The bottom line: there isn't a formula to calculate FWHP from RWHP...too many unknowns and too many variables, but it won't stop people from making up something.
07-01-2007, 03:42 PM
#12
Le Mans Master
I always use 15% for manuals and 20% for automatics.
07-01-2007, 03:44 PM
#13
Le Mans Master
Member Since: Jul 2005
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If you want RWHP, just put it on a chassis dyno.
If you're talking about FWHP from RWHP, some of it depends on the type of dyno used. A Mustang dyno can put a load on a car and control the rate of engine acceleration (250 RPM/sec, 500 RPM/sec or whatever) or it can hold the RPM constant. That way, HP loss due to the inertia of engine components, drivetrain components and wheels/tires/rotors are held constant. On a Dynojet dyno, there is only the inertia of the drum to resist the torque at the wheels so when we add more HP or dyno in a lower gear, the time for the dyno run is less which means more HP loss to inertia.
Drivetrain HP loss on a chassis dyno is composed of the following:
1) second order or exponential losses like friction
2) first order or linear losses like inertia and gears
3) constants like windage of gears through the oil in the transmission/differential, shafts rotating through seals, and sidewall flex all at a particular RPM. In other words, those losses are independent of HP transmitted.
That leaves us with the equation HP (loss)= ax^2+bx+c where a, b, and c are constants and x is FWHP. "c" is the predominate term meaning most of the HP loss is a constant.
Other variables to consider is when a dyno run is done in a lower gear, the tire, transmission shafts/gears, and differential shafts/gears RPM is less reducing the HP loss to sidewall flex/windage and giving more RWHP. On a Dynojet, this is countered by a shorter dyno run increasing loss to inertia, not a factor on a Mustang dyno though since it keeps the time of the dyno run constant. Conversely, a dyno run in 5th or 6th on a Dynojet will have less loss to inertia (longer dyno run time) but more loss to windage/tires...but there's also a speed limitation on chassis dynos which prevents a run in 6th (unless you have some 4.56s in the rear). On the road, quicker acceleration in the lower gears results in more loss (as a percentage) to inertia, the same effect as a Dynojet.
As far as the 1:1 ratio of 4th gear being the best to dyno in, there is fact as a basis to that statement. Quality involute gears have a HP loss of ~1%, so when we dyno in 1st, 2nd, 3rd, 5th, or 6th, part of the drivetrain loss is ~2% of the HP transmitted through any of those gears (it's 2% because power flows through one set of gears from the input shaft to the countershaft then through another set of gears from the countershaft to the output shaft). You may notice the distinct absence of 4th gear in the list above...that's because there are no "gears" for 4th gear, something a lot of people don't know. When you make the shift to 4th gear, the synchro mechanism mechanically couples/locks the input shaft to the output shaft and power flows straight through the transmission making 4th gear the most efficient "gear" to dyno a car in as far as the transmission is concerned. It doesn't have anything to do with the fact the "ratio" is 1:1 since we could also put the power through gears at a 1:1 ratio and achieve the same output RPM.
Hopefully this shines a little light on the subject, it's neither a percentage or a constant. But if you had to pick one, you'll be closer to FWHP if you use a constant. I.E. if you dyno a stock Z06 and come up with 450 RWHP for a 55 HP/10.9% loss, then mod it to 600 RWHP on the same dyno, you'll be much closer to the true FWHP if you add the 55 HP loss from stock rather than back calculate using the percentage number. And the guys mod their cars to 600+RWHP that just pull a percentage number out of their *** (like 15%) to back calculate their FWHP are just looking to stroke their ego with a big number and impress people. The only way to know the percentage is to remove the engine and put it on an engine dyno to get the FWHP. But then the first time you mod the engine, that number is not valid anymore. The bottom line: there isn't a formula to calculate FWHP from RWHP...too many unknowns and too many variables, but it won't stop people from making up something.
If you're talking about FWHP from RWHP, some of it depends on the type of dyno used. A Mustang dyno can put a load on a car and control the rate of engine acceleration (250 RPM/sec, 500 RPM/sec or whatever) or it can hold the RPM constant. That way, HP loss due to the inertia of engine components, drivetrain components and wheels/tires/rotors are held constant. On a Dynojet dyno, there is only the inertia of the drum to resist the torque at the wheels so when we add more HP or dyno in a lower gear, the time for the dyno run is less which means more HP loss to inertia.
Drivetrain HP loss on a chassis dyno is composed of the following:
1) second order or exponential losses like friction
2) first order or linear losses like inertia and gears
3) constants like windage of gears through the oil in the transmission/differential, shafts rotating through seals, and sidewall flex all at a particular RPM. In other words, those losses are independent of HP transmitted.
That leaves us with the equation HP (loss)= ax^2+bx+c where a, b, and c are constants and x is FWHP. "c" is the predominate term meaning most of the HP loss is a constant.
Other variables to consider is when a dyno run is done in a lower gear, the tire, transmission shafts/gears, and differential shafts/gears RPM is less reducing the HP loss to sidewall flex/windage and giving more RWHP. On a Dynojet, this is countered by a shorter dyno run increasing loss to inertia, not a factor on a Mustang dyno though since it keeps the time of the dyno run constant. Conversely, a dyno run in 5th or 6th on a Dynojet will have less loss to inertia (longer dyno run time) but more loss to windage/tires...but there's also a speed limitation on chassis dynos which prevents a run in 6th (unless you have some 4.56s in the rear). On the road, quicker acceleration in the lower gears results in more loss (as a percentage) to inertia, the same effect as a Dynojet.
As far as the 1:1 ratio of 4th gear being the best to dyno in, there is fact as a basis to that statement. Quality involute gears have a HP loss of ~1%, so when we dyno in 1st, 2nd, 3rd, 5th, or 6th, part of the drivetrain loss is ~2% of the HP transmitted through any of those gears (it's 2% because power flows through one set of gears from the input shaft to the countershaft then through another set of gears from the countershaft to the output shaft). You may notice the distinct absence of 4th gear in the list above...that's because there are no "gears" for 4th gear, something a lot of people don't know. When you make the shift to 4th gear, the synchro mechanism mechanically couples/locks the input shaft to the output shaft and power flows straight through the transmission making 4th gear the most efficient "gear" to dyno a car in as far as the transmission is concerned. It doesn't have anything to do with the fact the "ratio" is 1:1 since we could also put the power through gears at a 1:1 ratio and achieve the same output RPM.
Hopefully this shines a little light on the subject, it's neither a percentage or a constant. But if you had to pick one, you'll be closer to FWHP if you use a constant. I.E. if you dyno a stock Z06 and come up with 450 RWHP for a 55 HP/10.9% loss, then mod it to 600 RWHP on the same dyno, you'll be much closer to the true FWHP if you add the 55 HP loss from stock rather than back calculate using the percentage number. And the guys mod their cars to 600+RWHP that just pull a percentage number out of their *** (like 15%) to back calculate their FWHP are just looking to stroke their ego with a big number and impress people. The only way to know the percentage is to remove the engine and put it on an engine dyno to get the FWHP. But then the first time you mod the engine, that number is not valid anymore. The bottom line: there isn't a formula to calculate FWHP from RWHP...too many unknowns and too many variables, but it won't stop people from making up something.
...and since you said it so well, I'm staying out of this one!
07-01-2007, 04:49 PM
#15
For You "Enginerds" - or just the Knowledge Hungry or Curious
Start here:
http://en.wikipedia.org/wiki/Horsepower (good stuff)
Then Read:
http://www.superstang.com/horsepower.htm
And also:
http://forums.tdiclub.com/showthread.php?t=75062
and
http://www.answers.com/topic/horsepower?cat=technology
If you want to keep going:
http://www.freepatentsonline.com/3930409.html
http://en.wikipedia.org/wiki/Horsepower (good stuff)
Then Read:
http://www.superstang.com/horsepower.htm
And also:
http://forums.tdiclub.com/showthread.php?t=75062
and
http://www.answers.com/topic/horsepower?cat=technology
If you want to keep going:
http://www.freepatentsonline.com/3930409.html
07-01-2007, 05:37 PM
#18
Drifting
Member Since: Oct 2005
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07-05-2007, 09:22 AM
#20
Race Director
For a standard % you have to have standard equipment and conditions.
The closest to a standard on these Forums for the C6 seems to be a Dynojet with SAE corrected, smoothing 5. T/C & A/H off, large fan in front of the car, hood open. (And temps, etc. in a range where the ECM isn't pulling timing or adding fuel).
Standard transmissions Dyno 340 to 350 stock. 13% to 15% loss
Automatic transmissions Dyno 330 to 340 stock. 15% to 18% loss.
The closest to a standard on these Forums for the C6 seems to be a Dynojet with SAE corrected, smoothing 5. T/C & A/H off, large fan in front of the car, hood open. (And temps, etc. in a range where the ECM isn't pulling timing or adding fuel).
Standard transmissions Dyno 340 to 350 stock. 13% to 15% loss
Automatic transmissions Dyno 330 to 340 stock. 15% to 18% loss.