Intake Temperature v. HP
09-04-2008, 02:28 AM
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Intake Temperature v. HP
A friend and I were talking about our TTs and we both commented on how our cars seemed to respond much better on cooler days-no surprise there. So it lead us to wonder: does anyone know of a correlation/"rule of thumb" between the air intake temperature and horsepower, specifically with the 996TT? Obviously the cooler the air the more dense and intuition (as well as my butt dyno) tells me that there is a gain-but how much?
I'm sure the correlation is not linear. In other words the answer is not as simple as 10 hp for every 5 degree change in temp. Also, I think temperature differences will change HP differently depending on where they occur-the 10 degree difference between 90 and 80 should generate a greater HP gain/loss than the one between 60 and 50-or is this not correct? Is another consideration the HP rating-will higher HP cars see greater swings in their HP than those experienced by lower HP cars due to similar temperature drops?
Not looking for a big scientific explanation rooted in thermodynamic theory, but rather a simple rule of thumb as it related to our cars. But if someone takes the time to explain it scientifically I will surely read it.
Thanks in advance...
I'm sure the correlation is not linear. In other words the answer is not as simple as 10 hp for every 5 degree change in temp. Also, I think temperature differences will change HP differently depending on where they occur-the 10 degree difference between 90 and 80 should generate a greater HP gain/loss than the one between 60 and 50-or is this not correct? Is another consideration the HP rating-will higher HP cars see greater swings in their HP than those experienced by lower HP cars due to similar temperature drops?
Not looking for a big scientific explanation rooted in thermodynamic theory, but rather a simple rule of thumb as it related to our cars. But if someone takes the time to explain it scientifically I will surely read it.
Thanks in advance...
09-04-2008, 11:59 AM
#3
Very cool! 
Mike
Mike
09-04-2008, 12:10 PM
#4
Burning Brakes
Interesting app.
One comment I will make- this only tells you what the influence of air (temp, humidity, essentailly density) has on the HP output... if the DME is designed to more proactively pull timing as a 'protective feature' as temp increases, the effect of temp CAN be more dramatic. On NA cars it can be significant and dramatic.
A
One comment I will make- this only tells you what the influence of air (temp, humidity, essentailly density) has on the HP output... if the DME is designed to more proactively pull timing as a 'protective feature' as temp increases, the effect of temp CAN be more dramatic. On NA cars it can be significant and dramatic.
A
09-05-2008, 02:51 PM
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Interesting app.
One comment I will make- this only tells you what the influence of air (temp, humidity, essentailly density) has on the HP output... if the DME is designed to more proactively pull timing as a 'protective feature' as temp increases, the effect of temp CAN be more dramatic. On NA cars it can be significant and dramatic.
A
One comment I will make- this only tells you what the influence of air (temp, humidity, essentailly density) has on the HP output... if the DME is designed to more proactively pull timing as a 'protective feature' as temp increases, the effect of temp CAN be more dramatic. On NA cars it can be significant and dramatic.
A
09-05-2008, 09:00 PM
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Interesting app.
One comment I will make- this only tells you what the influence of air (temp, humidity, essentailly density) has on the HP output... if the DME is designed to more proactively pull timing as a 'protective feature' as temp increases, the effect of temp CAN be more dramatic. On NA cars it can be significant and dramatic.
A
One comment I will make- this only tells you what the influence of air (temp, humidity, essentailly density) has on the HP output... if the DME is designed to more proactively pull timing as a 'protective feature' as temp increases, the effect of temp CAN be more dramatic. On NA cars it can be significant and dramatic.
A
The variables that can be input in the calculator are the controlling elements of what is called density altitude. It illustrates how these variables impact power on a NA engine. But by looking at sea level, and keeping all inputs except temperature the same, you can see the impact temperature has on power.
09-06-2008, 02:11 AM
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It depends on what sort of setup and programming you have. A turbocharged 996TT with fixed boost control will perform better when it's hot because the ECU is not allowed to pull boost, only timing.
On a factory car ECU setup, when it is hot, the ECU will start by pulling timing and then it will pull boost aggressively if needed. This will result in lesser HP output than a fixed boost setup. TB993TT has a posted a very interesting table on the 993TT forum showing exactly how much timing and boost is being pulled by his ECU under different IATs, courtesy of a very expensive engine dyno with temperature control capability, not many of those around.
Obvious downside to this is the risk that you are running to detonate your engine if it is not carefully tuned. You will always see fixed boost engines being able to overtake variable boost ones in hot weather, especially in high speed runs under load. Air density calculations are accurate but only one part of the equation on turbo cars.
On a factory car ECU setup, when it is hot, the ECU will start by pulling timing and then it will pull boost aggressively if needed. This will result in lesser HP output than a fixed boost setup. TB993TT has a posted a very interesting table on the 993TT forum showing exactly how much timing and boost is being pulled by his ECU under different IATs, courtesy of a very expensive engine dyno with temperature control capability, not many of those around.
Obvious downside to this is the risk that you are running to detonate your engine if it is not carefully tuned. You will always see fixed boost engines being able to overtake variable boost ones in hot weather, especially in high speed runs under load. Air density calculations are accurate but only one part of the equation on turbo cars.
