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One more thought though... that is reasonably likely if you drive it under conditions that encourage it to learn your car and driving habits. A two hundred mile freeway cruise probably wouldn't do it, I would imagine a variety of conditions would be best being sure to include some full throttle runs as well (reasonably within speed limits and safe conditions of course!).
Sounds like you solved the problem. When I added an ECU tune to my car, it took a hundred miles or so before I felt a difference. Once I did, it was like day and night. It just takes a short while to adapt.
Sounds like you solved the problem. When I added an ECU tune to my car, it took a hundred miles or so before I felt a difference. Once I did, it was like day and night. It just takes a short while to adapt.
Yes. Its starting to respond a little better. I took a road to trip to Dallas and it had a little more pep. I still dont think it was like before. I guess heat can really be a factor.
Heat can be a really big factor. If you really want to get nerdy read some articles about "volumetric efficiency" and the how heat factors in the equation. Here is an article I used to turn my cars MAF/temp/rev/etc data into a volumetric efficiency calculation a few months ago: http://www.installuniversity.com/ins...n_9.012000.htm. The bottom line for our cars is that we get a lot of power out of a relatively small engine because our engines have unusually high volumetric efficiency (in other words, we get a lot more power out of our 3.8(or 3.6) liters of displacement than most cars with similar engine sizes.
If you are mathematically inclined and follow the equations, you can see that temperature has a big influence on the density of the air flowing into the intake by looking at Equation 1. Here are some sample densities at sea level at different temperatures:
- 32 degrees F: 0.08080 pounds per cubic foot.
- 77 degrees F: 0.07402 pounds per cubic foot.
- 95 degrees F: 0.07162 pounds per cubic foot.
In other words, at 95 degrees the air your car is pulling in is 11.37% less dense (0.07162/0.0808) than it is at 32 degrees, reducing the air flow and ultimately the volumetric efficiency by the same percentage. In other words, your car will have 11.37% less power at 95F than it has at 32F (at sea level). In a 997.2 Carrera S this is a whopping 44 horsepower difference.
Since the SAE says that the standard temperature for reporting horsepower readings is 77F (actually 25C) and Porsche reports a 997.2 Carrera S as having 385 HP (and I assume this uses the SAE standard), we can assume that at 95F our cars have only 373 horsepower (0.07162/0.07402*385). Of course going the other direction you can see that the engine has more horsepower when it is sucking in 32F air, roughly 417 horsepower.
So depending on when you last remember your car feeling especially fast you may certainly be feeling much of the loss from the Texas heat. Thanks for letting me be a nerd for a few minutes
I guess all of this explains why I got an especially good time in a test run of my car in the winter of 2014 in 44 degree temperatures using launch mode in Sport Plus. The app I use, which uses accelerometer data cross-correlated with GPS data over a quarter mile reported I ran a 3.86 second 0-60 and an 11.91 quarter mile at 115.7 mph. In the attached photos, three bars means it was a high quality run (the GPS data verified the accelerometer data it used gave it consistent readings). Yes, I know there could still be some error, but I have no doubt it was very close. You could feel it was a perfect launch. Note that the peak horsepower number you see on the display was the estimated rear-wheel horsepower based upon the weight of the car and driver I provided.
One more interesting thing to note: You can see the PDK shift points on the graph. Notice the forward acceleration G peaks on the graph when it shifts. Notice that there is no significant drop in Gs just before the peak when it shifts, something you would normally see if it was a manual tranny. That is where the PDK gets its 0.2 second typical advantage in 0-60.
Last edited by StormRune; Jun 15, 2015 at 07:40 PM.
pretty sure it is the battery disconnection. I also have a tip car and had the opposite problem - previous driver was a sunday driver type so when i got my car it was almost impossible to make it drop down a gear....
since then I disconnected the battery and after a few drives got it much better - then had to disconnect the battery for a light change and reverted back to the "safe mode".
I would recommend not worrying for a few days and if you want to speed up the process, drive the car in manual and keep in low gears if possible - plus do some hard acceleration(as if you don't do that already) I did this for a couple of drives and then amazingly the car then downshifted and kept itself in lower gears as standard...
Heat can be a really big factor. If you really want to get nerdy read some articles about "volumetric efficiency" and the how heat factors in the equation. Here is an article I used to turn my cars MAF/temp/rev/etc data into a volumetric efficiency calculation a few months ago: http://www.installuniversity.com/ins...n_9.012000.htm. The bottom line for our cars is that we get a lot of power out of a relatively small engine because our engines have unusually high volumetric efficiency (in other words, we get a lot more power out of our 3.8(or 3.6) liters of displacement than most cars with similar engine sizes.
If you are mathematically inclined and follow the equations, you can see that temperature has a big influence on the density of the air flowing into the intake by looking at Equation 1. Here are some sample densities at sea level at different temperatures:
- 32 degrees F: 0.08080 pounds per cubic foot.
- 77 degrees F: 0.07402 pounds per cubic foot.
- 95 degrees F: 0.07162 pounds per cubic foot.
In other words, at 95 degrees the air your car is pulling in is 11.37% less dense (0.07162/0.0808) than it is at 32 degrees, reducing the air flow and ultimately the volumetric efficiency by the same percentage. In other words, your car will have 11.37% less power at 95F than it has at 32F (at sea level). In a 997.2 Carrera S this is a whopping 44 horsepower difference.
Since the SAE says that the standard temperature for reporting horsepower readings is 77F (actually 25C) and Porsche reports a 997.2 Carrera S as having 385 HP (and I assume this uses the SAE standard), we can assume that at 95F our cars have only 373 horsepower (0.07162/0.07402*385). Of course going the other direction you can see that the engine has more horsepower when it is sucking in 32F air, roughly 417 horsepower.
So depending on when you last remember your car feeling especially fast you may certainly be feeling much of the loss from the Texas heat. Thanks for letting me be a nerd for a few minutes
I guess all of this explains why I got an especially good time in a test run of my car in the winter of 2014 in 44 degree temperatures using launch mode in Sport Plus. The app I use, which uses accelerometer data cross-correlated with GPS data over a quarter mile reported I ran a 3.86 second 0-60 and an 11.91 quarter mile at 115.7 mph. In the attached photos, three bars means it was a high quality run (the GPS data verified the accelerometer data it used gave it consistent readings). Yes, I know there could still be some error, but I have no doubt it was very close. You could feel it was a perfect launch. Note that the peak horsepower number you see on the display was the estimated rear-wheel horsepower based upon the weight of the car and driver I provided.
One more interesting thing to note: You can see the PDK shift points on the graph. Notice the forward acceleration G peaks on the graph when it shifts. Notice that there is no significant drop in Gs just before the peak when it shifts, something you would normally see if it was a manual tranny. That is where the PDK gets its 0.2 second typical advantage in 0-60.
It took me about two days to digest all this. So the hotter it gets, the slower my car is? That's interesting being that heat index was near 100.
Do you have PCCBs? Those look like 6 piston fronts.
No. I actually topped off my coolant not long ago, but I will check again. What will low coolant affect? Yes I do have PCCBs. 6 piston fronts good or bad??
It took me about two days to digest all this. So the hotter it gets, the slower my car is? That's interesting being that heat index was near 100.
Yep, you boiled it down nicely. At 100 degrees it is certainly no surprise you could feel some difference, but I'm pretty sure much of it was also explained by the battery disconnection and the relearning process.
And just to be a little more nerdy: at very high speeds in hot temperatures you'll get a little less drag since the air is less dense and easier for the car to push through, but its not enough to make up for the power loss to the engine.
Less dense?? Even with the humidity we have? Maybe I'm too dense😊
I'm afraid so. You are not dense... the answer just isn't intuitive. Disregarding humidity for a moment, hotter air is less dense because the molecules vibrate faster and that moves them further apart. As to humidity, I had to dig this up from Wikipedia (from this entry https://en.wikipedia.org/wiki/External_ballistics):
Air pressure, temperature, and humidity variations make up the ambient air density. Humidity has a counter intuitive impact. Since water vapor has a density of 0.8 grams per litre, while dry air averages about 1.225 grams per litre, higher humidity actually decreases the air density, and therefore decreases the drag.
I'm afraid so. You are not dense... the answer just isn't intuitive. Disregarding humidity for a moment, hotter air is less dense because the molecules vibrate faster and that moves them further apart. As to humidity, I had to dig this up from Wikipedia (from this entry https://en.wikipedia.org/wiki/External_ballistics):
Air pressure, temperature, and humidity variations make up the ambient air density. Humidity has a counter intuitive impact. Since water vapor has a density of 0.8 grams per litre, while dry air averages about 1.225 grams per litre, higher humidity actually decreases the air density, and therefore decreases the drag.
