I decided to move the posts about horsepower loss to a new topic.
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George - What is your "rule of thumb" for horsepower loss through the transaxle?
BD
BD
In regards to a Pantera, and a Pantera only,
rear wheel horsepower = 80% of flywheel horsepower.
Your friend on the DTBB, George
rear wheel horsepower = 80% of flywheel horsepower.
Your friend on the DTBB, George
HP loss is a fixed amount approximating between 100-125 hp lost in the drive train. You can't use a percentage because a car with 1000 hp would lose more, and a car with 300 hp would lose less. It is an estimated fixed amount, period, no percentage.
Ok, as RRS reasons, it seems to me it would be a fixed amount rather than a percentage. Dennis Quella at PPC in Castle Rock, CO. told me about 90 - 100 horsepower. I know that he has built several motors and run them on a dyno and probably a chassis dyno. What prompted the question was the comment above about 308bhp and 262 at the wheels. That is only 46 hp loss through the drive train. Thanks to all who commented.
Logically, I'd like to agree that it is closer to a fixed HP amount. Does anyone have any empirical data to support this?
Jeff
6559
Jeff
6559
Wow, so the average parasitic loss for the the ZF car aproaches 20% or more? That's significant, perhaps worse than a RWD Ford with a Toploader and TL or DL rear. Who has actually tested that in a Pantera? I'd love tosee the actual dyno results. More conventional cars with T5Z or Tremics in a RWD configuration generally see ~18%. And while parasitic loss is somewhat fixed, the difference in the real world if you are talking 300HP, 400HP, 500HP remains fairly constant. If you are talking a 3.33x spread in HP like from 300 to 1000, then yes, the factor will change.
quote:Originally posted by BD:
George - What is your "rule of thumb" for horsepower loss through the transaxle?
BD
This has been discussed for years on both forums with a range of values from 20 to 25%. The commonly used estimate is 22%. Some, even, have suggested that it is not a percentage but a relatively fixed HP loss.
To the best of my knowledge, no one has actually tested this. Sounds like a good project.
Jeff
6559
Over the years, a few Pantera owners have provided both engine dyno & chassis dyno numbers to PI magazine, when PI has done an article about their car. I have noticed, in regards to Panteras with motors from 280 bhp to 550 bhp, that the number always hovers around 20%, not a fixed amount.
Argue all you want, that is what I've observed. If you don't believe me, thumb through your back issues of PI. It is logical to me the loss would be fixed, but the data says the opposite.
Mind you, there are ALWAYS some differences in testing an engine on an engine dyno & a chassis dyno that will create horsepower loss not associated with the drivetrain, for instance two differences that come immediately to mind are that the engine dyno normally has a less restrictive exhaust system and when mounted in the Pantera engine bay the motor normally inhales much warmer air.
John, my experience with front engine rear wheel drive cars is greater losses than that, in the neighborhood of 25%.
Your friend on the DTBB, George
Argue all you want, that is what I've observed. If you don't believe me, thumb through your back issues of PI. It is logical to me the loss would be fixed, but the data says the opposite.
Mind you, there are ALWAYS some differences in testing an engine on an engine dyno & a chassis dyno that will create horsepower loss not associated with the drivetrain, for instance two differences that come immediately to mind are that the engine dyno normally has a less restrictive exhaust system and when mounted in the Pantera engine bay the motor normally inhales much warmer air.
John, my experience with front engine rear wheel drive cars is greater losses than that, in the neighborhood of 25%.
Your friend on the DTBB, George
Rapier - How did they measure the engine power? Or, could you explain the difference between engine power and wheel power?
BD,
I'm not an expert on this one - but I know the basics.
This was a rolling road type dynamometer.
It measures the power output at the wheels.
At the end of the test they do a 'run down' test which gives them a value for the drive train losses. This value is used to calculate the engine power.
If properly done this should give an accurate measure of the engine power.
If you took your engine out and measured on an engine dynamometer the reading should be very much the same as the calculated engine power reading from the rolling road dynamometer.
The whole thing is inexact as even your tyre pressures will affect the dyno reading.
There is a nice explanation this stuff on this web page:
http://www.emeraldm3d.com/em_r_road.html
Lastly - to add my 2 cents.
Though it sounds logical that the losses are fixed - it's still the same transmission etc - it cannot be. This would mean producing more than 100bhp just to move the car at walking speed. There are plenty of small cars produce far less than 100bhp - could their losses be so much smaller than a ZF.
I'm not an expert on this one - but I know the basics.
This was a rolling road type dynamometer.
It measures the power output at the wheels.
At the end of the test they do a 'run down' test which gives them a value for the drive train losses. This value is used to calculate the engine power.
If properly done this should give an accurate measure of the engine power.
If you took your engine out and measured on an engine dynamometer the reading should be very much the same as the calculated engine power reading from the rolling road dynamometer.
The whole thing is inexact as even your tyre pressures will affect the dyno reading.
There is a nice explanation this stuff on this web page:
http://www.emeraldm3d.com/em_r_road.html
Lastly - to add my 2 cents.
Though it sounds logical that the losses are fixed - it's still the same transmission etc - it cannot be. This would mean producing more than 100bhp just to move the car at walking speed. There are plenty of small cars produce far less than 100bhp - could their losses be so much smaller than a ZF.
quote:Originally posted by Rapier:
Lastly - to add my 2 cents.
Though it sounds logical that the losses are fixed - it's still the same transmission etc - it cannot be. This would mean producing more than 100bhp just to move the car at walking speed. There are plenty of small cars produce far less than 100bhp - could their losses be so much smaller than a ZF.
Good observation Derek,
The friction in a transmission will increase with rpm AND with power transmitted (loading).
This is why a trans oil circulation pump & oil cooler are needed when the car is raced. If the friction remained the same, no cooler would ever be needed. The fact there is more heat in the oil indicates whatever creates the heat has increased, i.e. friction.
That heat is horsepower that is lost in the transmission, the more heat (btu's), the more horsepower that is lost. The fact that high rpm & high loads create more heat in the tranny indicates these conditions also create more horsepower loss, it is not a fixed amount.
Your friend on the DTBB, George
There may be enough difference between chasis dyno's and engine dyno's to cause more confusion then they clear up. None the lest I still think we could use a sticky or a spot just for posting this info.