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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > How much power do we lose when its hot outside?



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      07-07-2007, 12:37 PM   #23
eLEkTrONIkLY_LTD
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I live in AZ where temps lately have been 115°+ and from spring to summer I have noticed a significant decrease in power. The heat coupled with the parasitic effect of the A/C definitely hinders the pavement peeling here in the desert.
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      07-07-2007, 01:07 PM   #24
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FI engine lose more power at higher temps than NA engines? Anybody know why?
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      07-07-2007, 01:26 PM   #25
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Quote:
Originally Posted by zenmaster View Post
What has been covered was how and why turbo engine loses power, but one of the questions was "I know turbo cars loose more power than NA engines at higher temps, but does anyone have any idea how much power we are losing". This has yet to be answered.
And, again, as has been discussed, there are way too many variables to answer that question. Temperature outside, temperature of car's coolant, degree of heat soak your intercooler is seeing at that moment, altitude, boost, rpm, etc., etc. You'd also have to be specifically talking about our exact engine. If not, add in displacement, efficiency, number of turbos, type of fueling system, etc.

Basically, heat sucks for turbo cars. Hotter air is less dense air. Difficult to calculate the exact loss, but who really cares?
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      07-07-2007, 01:34 PM   #26
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My car did 275whp on the dyno in 95 degree heat... (uncorrected)... I only lost 2 hp on the 2nd and 3rd run because they were only a few seconds apart, and the car was heatsoaked.

I would say that the loss is minimal until you get pretty high above that.
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      07-07-2007, 01:52 PM   #27
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Quote:
Originally Posted by kptaylor View Post
Basically, heat sucks for turbo cars.
Those with experience tuning and dynoing a car through various incremental HP upgrades get a feeling for how much more power the car is producing simply by way of its acceleration. On a hot day, they might notice that the acceleration is back to was when making X HP. Given that less than 10HP is not very noticeable, someone experienced with modding their car could tell you, probably within 10HP, what the negative or positive affect of ambient temp was.

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Originally Posted by RiXst3r
My car did 275whp on the dyno in 95 degree heat... (uncorrected)... I only lost 2 hp on the 2nd and 3rd run because they were only a few seconds apart, and the car was heatsoaked.
The car will also be heatsoaked if you take it for a 30minute drive in 90degree heat. Dyno it then. The effect will be more like 20-25hp, not 2 hp. Dyno and drag racing are not the way to measure hp loss due to ambient temp, because no one wants to waste money running in these conditions.
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      07-07-2007, 06:52 PM   #28
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Just a gut feel, but the power difference between 75 degrees and 20% humidity and 95 degrees and 90% humidity is very noticable.
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      07-09-2007, 09:20 AM   #29
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FI engine lose more power at higher temps than NA engines? Anybody know why?
It's because the air is compressed by the turbos. The hot, compressed air is less efficient than hot air that is not compressed (cooler, more dense).
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      07-09-2007, 12:22 PM   #30
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FI engine lose more power at higher temps than NA engines? Anybody know why?
FI having IC is dependent on cool air hitting the IC. IC does not perform well without cool air. That problem does not exist in NA.
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      07-09-2007, 12:23 PM   #31
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At least 30hp, because I have turn on my A/C.
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      07-09-2007, 12:34 PM   #32
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Quote:
Originally Posted by RiXst3r View Post
My car did 275whp on the dyno in 95 degree heat... (uncorrected)... I only lost 2 hp on the 2nd and 3rd run because they were only a few seconds apart, and the car was heatsoaked.

I would say that the loss is minimal until you get pretty high above that.
So the dyno fan blew air to your IC that was just slightly warmer at the last run. Heatsoak hits already before the end of the first dyno run. IATs are thus not much different between the runs. As the ambient temps are close to each other across the runs, your experiment does not tell much about ambient temps effect.
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