Just Dyno tested my 997 S, with stock 355 HP. The Dyno showed only 317 HP

The car runs great and it was very surprising that it didn’t have all of its 355 HP.

The Dynometer is also correct.

What is wrong……? Can anybody help me..?

 

haa....the 317hp is power @ the rear wheels....the 355hp is stated @ the crank

no worries this is normal

 

In fact 317 BHP (wheels) is a good result - the 997S in standard trim typically shows about 10-12 less than that.

 

No that not it…

Because all of my numbers was in DIN HP (Europe)

If I convert them to your standard SAE (USA standard) is a lot smaller. Maybe about 275 SAE HP

 

bring it to the dealer and get your money back...

 

they accidentally put an "S" behind the carrera badge on your car...

 

Can u say "refund-lemon law"

 

317hp din converted to sae is 312.654hp (SAE = DIN/1.0139)

stop worrying your cars hp numbers are perfectly normal

 

To convert from crankshaft horsepower to rear wheel horsepower, factor by 16 to 17 percent(.84 or .83) for two wheel drive or 20(.8) percent for four wheel drive. Use the reciprocal in the other direction.

Power and torque figures will vary widely, depending on the particular dyno, the day, the atmospheric conditions and how the operator sets up the car on the machine. No dynamometer is ever "correct".

Your dyno readings for rwhp look optimistic for 355 cshp.

To say that dyno testing is not an exact science is an understatement.

 

317 sounds pretty healthy!

 

There is northing wrong with the Dyno. He uses it everyday and all other cars, also that day (yesterday) showed the right numbers. I am not sure have to calculate from Europe HP to Your USA HP, but anyway, from Porsche the car has 355 DIN HP (Europe) , and we use only that way in Europe when we do the Dyno, it showing the HP in DIN.

So we are back from where I started, The car is missing about 40 HP. So if somebody have a suggesting of what there can be wrong I will be very happy. The cars is out of guaranty so it is coming out of my own pocket…!

I was thinking maybe the mas flow was not working……

 

Do you understand the difference between crank-horsepower (CHP) and wheel-horsepower (WHP)?

 

There's nothing wrong with your car's horsepower. If you don't believe it, find a car magazine that tests the rolling start/overtake 45-70mph (or similar) elapsed time in top gear and compare it to your car. You should get the same elapsed time. There should be less variability from driver to driver in this test than the 0-60mph test.

 

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.

 

There are no "right" numbers with dynoes. The machine you had your car tested on is very optimistic. Given a loss factor of 16 percent, the crankshaft power is 1/.84=1.19 of the rear wheel power, which is 377 cshp(claimed 355). On a conservative dyno, 997S's generally show 295 to 305 rwhp in stock configuration.