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I did some tests with my M5 last week, with >25°C temp, and never managed to do better than 19.5 sec for 0-200 kph.
This evening the weather was much colder, and at the same place as before i did some run again 0-200 kph, but with 7°C temp.
Around 18.5 sec easily !!

I think i've heard that engines work better with fresher air, but why ??
It seems that it makes big differences..
 

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The reason is that the colder air is more dense, therefore containing more oxygen at a given volume. The air mass meter tells the computer this and it adds more gas. So now you get a bigger explosion and more power. I live in Houston, Texas where it is 100 degrees F and 95% humidity in the summer, and I definitely notice a decrease in power. The humidity is also a big factor because the water displaces the air.
 

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So JEFF basically what u're saying is that this car is worthless for people who live in hot climates all yr round? And i personally thought as long as i remember that u should take out your "SPIFFY" car in warm climates to show it off....hmm, what a dissapointment. I live in NYC and everyone knows that the weather here can get very disgustingly nastily HOTTT and sticky, all due to humidity. I know what u mean JEFF. I used to live in SPRING, TX and i know what its like. Damn, what a true oxymoron....taking your car out in the cold, snowy weather just to get more power and feel the true extend of this car. I'll remember that when and if my dealer ever plans on delivering me my damn car!!!! I guess i'll just keep it garaged during the summer.....HAHAHAHA....
 

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So JEFF basically what u're saying is that this car is worthless for people who live in hot climates all yr round? And i personally thought as long as i remember that u should take out your "SPIFFY" car in warm climates to show it off....hmm, what a dissapointment. I live in NYC and everyone knows that the weather here can get very disgustingly nastily HOTTT and sticky, all due to humidity. So not only do i I know what u mean JEFF but i live it. I also used to live in SPRING, TX and i know what u're going through. Damn, what a true oxymoron....taking your car out in the cold, snowy weather just to get more power and feel the true extent of this car. I'll remember that when and if my dealer ever plans on delivering me my damn car!!!! I guess i'll just keep it garaged during the summer.....HAHAHAHA....
 

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Combustion engine works on the principle that there must be two different thermal stores (I don't know correct english words for these things). The another "store" is the air outside the engine (outside the tailpipes) and the other is in the motor. There must be temperature diffence between these two "stores" or the engine won't work. Efficiency can be calculated: n=[T(1)-T(2)]/T(1). And Ts are given in Kelvins. So in 25°C temp (=298.15K) efficiency is n=[T(1)-298.15K]/T(1), I don't know how hot the engine is, but for example we can think it's 1000K, so we get n=1000K-298.15K/1000K=0.70185. In outside temperature of 7°C (=280.15K) n=1000K-280.15K/1000K=0.71985. As we can see here the engine is working better in colder (better efficiency=n), but we won't notice this big diffence in the real world because other parts of the car can be stiffer in cold weather.
I hope this explained something, personally I don't know how humidity affects on the engine but I guess it makes a difference too.
 

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the difference is only a few HP... it's not like your V8 will turn into a inline 4 during the summer...
 

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Power can vary as much as 2% every 10deg (Farenheit). So all naturally aspirated engines (maybe forced induction suffers less in relative terms) will feel less powerful when it is hot and humid. So Tom, you experienced over 6% power difference (which explains your numbers).

Dan
 
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