Today we had a cool front blow through and WOW, what a difference in power the EVO makes when it is cool! I have always noticed that cooler weather makes more power but the EVO really likes it! I guess the combination of the denser air as well as the intercooler working more efficiently is what makes it so noticable. I would say 30hp on the butt dyno...

 

I wonder what the threshholds are for the temp differences. Is there a point where it's TOO cold and performance begins to be ill effected?
While we're on topic with weather, what about humidity? What kind of differences can one expect between a day with 80% vs 10%? Assuming all other conditions, temp, altitude etc is constant.

 

Does the weather affect FI cars more than NA cars?

 

Uh Fuel Injected Cars can be Normally Aspirated or Charged.. and Carburated Cars can be Normally Aspirated or Chargeed...

 

uh, I'm pretty sure he means:
FI = Forced Induction

 

Difference in air temperature affects ALL combustion engines. Refer to your thermodynamics text for the Universal Gas Law: PV=nRT, where T=difference in temp.

 

At 68 degrees F, and standard atmospheric pressure of 760 mm Hg, 100% relative humidity corresponds to 17.5 mm Hg of water vapor pressure. This means that 17.5/760 = 2.3% of the air your engine is sucking in is actually water, which is useless to your engine. So the difference in actual combustible air intake to the engine at 68 degrees and standard atmospheric pressure is 2.3%, and you'll see about a 2.3% difference in horsepower between 0% and 100% relative humidity (assuming that your engine is running rich like the Evo does at high speed, air intake is the main limiting factor to horsepower).

For your question, between 10% and 80% relative humidity, take 0.7 x 2.3%, which is about 1.6%. Given the Evo's 271 hp rating, you're looking at about a 4 horsepower gain with the drier air.

As the temperature goes up, the difference in horsepower becomes more pronounced, since the moisture capacity of the air goes up.

 

Thanks, that's exactly what I wanted!

 

All I know is that since I bought my EVO about two weeks ago, it has been in the low to mid 90's. This morning it was 68 degrees and man, what a difference! The humidity is much lower as well...