Carrera S, loose in power.
#33
09-24-2008, 01:16 AM
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.
Finally one who gets the point, that’s exactly have the Dyno works. And if it was 10 Hp wrong it didn’t matter, but 40 HP is too much I think.
Has anybody tried to run it out in high gear? What will the car show at the Speedo in normal weather….???
#35
12-15-2008, 07:14 AM
Dyno
The dyno is not the problem, i'm pretty sure. I've had a Porsche Boxster 2,7 on the same Dyno as Kenn, and the result was 219,2 bhp - Porsche say 220 bhp.
I've had a lot of cars on the same dyno (Landberg.dk), and the output is very reliable, so the problem must lie somewhere else... Can it be the cooling of the engine on the dyno?
I've had a lot of cars on the same dyno (Landberg.dk), and the output is very reliable, so the problem must lie somewhere else... Can it be the cooling of the engine on the dyno?
#37
12-15-2008, 07:45 AM
The Dyno I working perfectly…..
2 month ago I got I new mass-flow (air intake measure) and went to THE SAME DYNO again and the car was only missing 15 HP..
So that was the problem. The 15 HP is within the range of the stock HP. And finally I tried to run the car out, and it shoved 300 km/t and the RPM was at max. (Maybe 304 km/t if I tried a little more)
I am very satisfied with the car now as you can imaging
2 month ago I got I new mass-flow (air intake measure) and went to THE SAME DYNO again and the car was only missing 15 HP..
So that was the problem. The 15 HP is within the range of the stock HP. And finally I tried to run the car out, and it shoved 300 km/t and the RPM was at max. (Maybe 304 km/t if I tried a little more)
I am very satisfied with the car now as you can imaging
#38
12-15-2008, 01:36 PM
Super! Then there WERE a problem with the engine... Good news! Good to hear the horses are back where they belong... 
It might be useful information for others as well...
It might be useful information for others as well...
#39
12-16-2008, 05:46 AM
It's a fine result that does NOT indicate any problem or deficiency, but you also didn't include some important info, including the fuel used, air temperature, humidity, atmospheric pressure, engine water/oil temp to just name a few that could affect the results.
#40
12-16-2008, 05:54 AM
Especially if other cars on the same dyno achieve results closer to factory spec.
#41
12-17-2008, 03:49 AM
I think I might know what's happening here. I really doubt it is your car that is at fault - I'd put big money on it being bad dyno practice! The 997S on a dyno is extremely sensitive to intake air temps and coolant temps. If either of these go above what is experienced on the road - even by a small margin - the car's ECU will pull timing and richen the mixture to prevent engine detonation. This results in a big drop in power.
Now the 911's cooling isn't the best even under ideal conditions (witness the need for an additional radiator on X-51 to handle only 26 extra BHP) and on a dyno the temps can soar very quickly indeed. These cars need to be dyno'd with huge fans on each rad and an additional one by the air intake. Both coolant temps and intake air temps need to be monitored continuously, as does lambda and ignition timing. If high temps and any movement in lambda or timing from norm is seen, the run needs to be aborted as it is meaningless. I'd bet the farm that your dyno operator isn't taking any of these essential precautions and that's why your car appears down on power.
Regarding the other cars you mentioned - front engined, intake facing forward; one large fan in front of the car will often be enough to give a resonable result. Just remember the 911 is very different here and has to be treated very differently to get the correct result
Now the 911's cooling isn't the best even under ideal conditions (witness the need for an additional radiator on X-51 to handle only 26 extra BHP) and on a dyno the temps can soar very quickly indeed. These cars need to be dyno'd with huge fans on each rad and an additional one by the air intake. Both coolant temps and intake air temps need to be monitored continuously, as does lambda and ignition timing. If high temps and any movement in lambda or timing from norm is seen, the run needs to be aborted as it is meaningless. I'd bet the farm that your dyno operator isn't taking any of these essential precautions and that's why your car appears down on power.
Regarding the other cars you mentioned - front engined, intake facing forward; one large fan in front of the car will often be enough to give a resonable result. Just remember the 911 is very different here and has to be treated very differently to get the correct result
#42
12-17-2008, 04:19 AM
I think I might know what's happening here. I really doubt it is your car that is at fault - I'd put big money on it being bad dyno practice! The 997S on a dyno is extremely sensitive to intake air temps and coolant temps. If either of these go above what is experienced on the road - even by a small margin - the car's ECU will pull timing and richen the mixture to prevent engine detonation. This results in a big drop in power.
Now the 911's cooling isn't the best even under ideal conditions (witness the need for an additional radiator on X-51 to handle only 26 extra BHP) and on a dyno the temps can soar very quickly indeed. These cars need to be dyno'd with huge fans on each rad and an additional one by the air intake. Both coolant temps and intake air temps need to be monitored continuously, as does lambda and ignition timing. If high temps and any movement in lambda or timing from norm is seen, the run needs to be aborted as it is meaningless. I'd bet the farm that your dyno operator isn't taking any of these essential precautions and that's why your car appears down on power.
Regarding the other cars you mentioned - front engined, intake facing forward; one large fan in front of the car will often be enough to give a resonable result. Just remember the 911 is very different here and has to be treated very differently to get the correct result
Now the 911's cooling isn't the best even under ideal conditions (witness the need for an additional radiator on X-51 to handle only 26 extra BHP) and on a dyno the temps can soar very quickly indeed. These cars need to be dyno'd with huge fans on each rad and an additional one by the air intake. Both coolant temps and intake air temps need to be monitored continuously, as does lambda and ignition timing. If high temps and any movement in lambda or timing from norm is seen, the run needs to be aborted as it is meaningless. I'd bet the farm that your dyno operator isn't taking any of these essential precautions and that's why your car appears down on power.
Regarding the other cars you mentioned - front engined, intake facing forward; one large fan in front of the car will often be enough to give a resonable result. Just remember the 911 is very different here and has to be treated very differently to get the correct result
That also explains have the car with now problems went to max speed 300 km/t and max rpm. in high gear, on the high way, and that’s was before the new mass flow.
And yes, my dyno operator has never tested a 911 before so we didn’t now that the car was so sensitive with temperature.
Last edited by sofekba; 12-17-2008 at 04:49 AM.
#45
12-28-2008, 10:52 AM
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