Carrera S, loose in power.
#16
09-22-2008, 12:20 PM
And it is crank horsepower I am talking about, that’s the problem. If it was on the wheels HP, no problems, but is not.
The dyno is measure the los in transmission on so on, so that the HP number will be close to the factory. But this is the first time of the 7 to 8 times that I have been to that dyno, (other cars) and the car didn’t showed the right Hp numbers.
There fore, what can be wrong ….??
#19
09-23-2008, 12:11 AM
DIN HP figures are just a measure of units of energy expended in a specific unit of time. There's no myth about them and they aren't a set of standards as to how the dyno is corrected or anything of that type. DIN also doesn't define where the HP is measured. You can measure the number of DIN HP anything produces just about anywhere! Have a look at this site:
http://www.statman.info/conversions/power.html
1 DIN HP simply = 735.4988 Watts
Now on a dyno you can only take a measure of the cars output at the wheels (or hubs, depending on the dyno type). The dyno measures the car's output in watts then the computer divides this by 735.4988 to give you a DIN HP figure. This will be lower than the manufacturer figure because of frictional losses in the transmission, driveshafts, wheel bearings and tyres on the rollers.
Manufacturers measure the engine output on an engine dyno. Here there is no transmission attached to the engine - the output is measured directly off the flywheel without having to turn all the gears and wheel hubs etc. All the temperatures are also strictly controlled to give accurate repeatable results. This output in watts is then also divided by 735.4988 to give a DIN HP figure.
The only difference between DIN HP (or PS as it is also known) and SAE HP is that 1 SAE HP is a different number of Watts, in this case 745.70. This means a DIN HP is simply 0.986 of an SAE HP.
So your result of 317 wheel DIN HP = 312.6 wheel SAE BHP
Porsche's quoted output is 355 crank DIN HP or about 350 crank SAE HP
There typically seems to be approx 16% of the 997S's power lost to transmission friction. If your dyno result is 'correct' (and I agree with previous contributors to this thread, there are no real absolutes - it's just too difficult to keep all the important parameters under control) then your crank figure (to compare to Porsche's quoted output of 355 DIN HP) would be approx 368 DIN HP. A good result for a standard 997S.
http://www.statman.info/conversions/power.html
1 DIN HP simply = 735.4988 Watts
Now on a dyno you can only take a measure of the cars output at the wheels (or hubs, depending on the dyno type). The dyno measures the car's output in watts then the computer divides this by 735.4988 to give you a DIN HP figure. This will be lower than the manufacturer figure because of frictional losses in the transmission, driveshafts, wheel bearings and tyres on the rollers.
Manufacturers measure the engine output on an engine dyno. Here there is no transmission attached to the engine - the output is measured directly off the flywheel without having to turn all the gears and wheel hubs etc. All the temperatures are also strictly controlled to give accurate repeatable results. This output in watts is then also divided by 735.4988 to give a DIN HP figure.
The only difference between DIN HP (or PS as it is also known) and SAE HP is that 1 SAE HP is a different number of Watts, in this case 745.70. This means a DIN HP is simply 0.986 of an SAE HP.
So your result of 317 wheel DIN HP = 312.6 wheel SAE BHP
Porsche's quoted output is 355 crank DIN HP or about 350 crank SAE HP
There typically seems to be approx 16% of the 997S's power lost to transmission friction. If your dyno result is 'correct' (and I agree with previous contributors to this thread, there are no real absolutes - it's just too difficult to keep all the important parameters under control) then your crank figure (to compare to Porsche's quoted output of 355 DIN HP) would be approx 368 DIN HP. A good result for a standard 997S.
I understand what you are writhing, but please read my last post, and maybe you can tell me what could be wrong. Maybe the massflow is not working…..??
#21
09-23-2008, 04:50 AM
Yes……
And it is crank horsepower I am talking about, that’s the problem. If it was on the wheels HP, no problems, but is not.
The dyno is measure the los in transmission on so on, so that the HP number will be close to the factory. But this is the first time of the 7 to 8 times that I have been to that dyno, (other cars) and the car didn’t showed the right Hp numbers.
There fore, what can be wrong ….??
And it is crank horsepower I am talking about, that’s the problem. If it was on the wheels HP, no problems, but is not.
The dyno is measure the los in transmission on so on, so that the HP number will be close to the factory. But this is the first time of the 7 to 8 times that I have been to that dyno, (other cars) and the car didn’t showed the right Hp numbers.
There fore, what can be wrong ….??
The rest of the horses are hiding in the clutch, transmission, axles and tires.
#22
09-23-2008, 07:23 AM
So are you saying that the engine has been removed from the car and that is what is on the Dynomometer? The usual set up is to put the car on the Dyno and spin the rear wheels against a known resistance. That measures rear wheel HP. Crank Horsepower can only be measured on a stand in a test lab and it is under ideal conditions.
The rest of the horses are hiding in the clutch, transmission, axles and tires.
The rest of the horses are hiding in the clutch, transmission, axles and tires.
“The Dyno is measure the los in transmission on so on, so that the HP number will be close to the factory. But this is the first time of the 7 to 8 times that I have been to that Dyno, (with other cars) and the car didn’t show the right Hp numbers.”
Try and forget about the wheel and the crank power I take note of what it is I am writing instead.
With every other car that is being Dyno tested on that dyno the HP is about the same as the factory HP. I he uses it everyday.
Let me explain
If he Dyno tested a BMW M5 form 2005 it will show about 500 HP, Factory says 507 HP, so OK
If he Dyno tested a VW golf GTI form 2006 it will show 205 HP, factory says 200 HP so also OK
And my 997 S is showing 317 when it shut be 355
Do you get the picture…..!!!
#25
09-23-2008, 01:30 PM
I'm surprised everyone is so patient with this guy...I've seen worse reactions for less...
Is this a joke?...like the 911 Ring license plate???
Is this a joke?...like the 911 Ring license plate???
#26
09-23-2008, 03:37 PM
Try and forget about the wheel and the crank power I take note of what it is I am writing instead.
Okay, but what you are writing doesn't make sense
With every other car that is being Dyno tested on that dyno the HP is about the same as the factory HP. I he uses it everyday.
If an M5 is advertised as 500HP and the Dyno reads 500HP then there is a correction factor built into the software to account for transmission losses. Perhaps the correction factor in the software wasn't turned on when they ran your machine.
The fact remains that although Porsche advertises a 355 HP engine in the Carrera S, that the rear wheels only transmit about 315 to the pavement.
Okay, but what you are writing doesn't make sense
With every other car that is being Dyno tested on that dyno the HP is about the same as the factory HP. I he uses it everyday.
If an M5 is advertised as 500HP and the Dyno reads 500HP then there is a correction factor built into the software to account for transmission losses. Perhaps the correction factor in the software wasn't turned on when they ran your machine.
The fact remains that although Porsche advertises a 355 HP engine in the Carrera S, that the rear wheels only transmit about 315 to the pavement.
#28
09-23-2008, 06:20 PM
Don't be so hard on the guy. I *think* he knows what he's talking about, and the rest of you are missing the point.
IIRC, when you're doing a dyno test, you can finish your run, then put the car in neutral, and let it coast down back to idle. The drag in the driveline makes this happen faster than the rollers would naturally lose their inertia, which lets you estimate the drivetrain loss, which can then be used to get the dyno to output crank HP, as opposed to wheel HP. Yes, it's a guesstimate, but it shouldn't be 40HP off.
If you can, get the uncorrected, raw wheel-horsepower estimate, as that's the number that better correlates to expected performance.
Or, go to a dragstrip, and make a couple of passes. Even if you're a rank amateur, your trap speed will indicate horsepower. If that number is significantly lower than the usual figures, you've definitely got a problem.
IIRC, when you're doing a dyno test, you can finish your run, then put the car in neutral, and let it coast down back to idle. The drag in the driveline makes this happen faster than the rollers would naturally lose their inertia, which lets you estimate the drivetrain loss, which can then be used to get the dyno to output crank HP, as opposed to wheel HP. Yes, it's a guesstimate, but it shouldn't be 40HP off.
If you can, get the uncorrected, raw wheel-horsepower estimate, as that's the number that better correlates to expected performance.
Or, go to a dragstrip, and make a couple of passes. Even if you're a rank amateur, your trap speed will indicate horsepower. If that number is significantly lower than the usual figures, you've definitely got a problem.
#29
09-23-2008, 07:17 PM
Maybe you should try a few other dyno shops and compare results. Maybe it was THEIR machine that was off and not your Porsche. But who knows, maybe you really did get short changed.
