More Power in Colder Weather?
 

My brother and I were talking this weekend and the topic of engine output came up. We all know that intercoolers are in place to lower the air temp. on supercharged or turbocharged engines because lower air temps allow a better air/fuel mixture.

So would a normally aspirated (or non-intercooled) engine create more power in the winter months (air temp. at let's say 35 degrees F) than in the summer (at 95 degrees F)?

Probably a negligible amount I would think. There is a big difference in ambient temp and the temp that even normally aspirated engines run at, never mind turbocharged air. I don't know.

Sure, but, if the computer can't take advantage of the cooler air, by either adding fuel, and/or advancing spark timing, then the answer is a "not really." If either you can tune via software and a laptop, or the computer in the car can take advantage of all that...then you bet. Cooler temps can produce noticable amounts of power.

Intake air temp is one of the parameters that is used to calculate fuel input. So yes, even without manual tuning, cooler (denser) ambient air will create some additional power output. Whether or not it's noticeable is another question.

The flipside is, of course that warmer weather and thinner air (as at high altitudes) rob power.It doesn't make for huge gains, but sure there's a bit more power in colder weather.

I have no doubt at all that I have often felt power increase from lower outside air temps with my official "butt dyno", even on older NA engines. The denser air allows more air and more fuel so even with rudimentary ECU compensation the motor will make more power. Did you even notice how even just moist air, like when it's raining or misty outside, makes more power?

With my current turbocharged car, I'm guessing the difference between 35F and 95F outside air temp is well over 20hp (out of about 500hp it typically makes).

The rule of thumb I've heard is that every 10° you drop gives you roughly a 1% increase in peak power.

Thanks ...now that you mentioned it, I remember hearing that rule of thumb before. I'll recalibrate my butt dyno since that would be about 30hp taking 6% of 500.

Thanks for verifying for me.

Now, why isn't there more racing done in cold weather? Is it just because the tires won't warm up?

Because the weather's too unpredictable. Organized races have a lot going on behind the scenes and it's simply impossible to pull it all together without setting a specific day to do it on. So organizers do that and hope for an optimal day.

If you mean why isn't racing done in the winter season, that would be due to the possibility of glare ice and snow and other such nastiness on the track. Slicks on anything but clean, dry asphalt will result in a sliding, spinng, flipping, crashing car.

huh?
 

Why would moist air make more power? You can't burn the water in the air. I would think cold, dry air (more densely packed oxygen molecules) would be ideal.

I can definitely tell the difference in my current car ('96 Mustang Cobra) and I remember being able to tell in my old '85 200SX.

Well you seem to be correct. I'm sure there are plenty of these calculators around but I found this interesting little page and if I put in higher relative humidity, the relative power goes down slightly http://wahiduddin.net/calc/calc_hp_abs.htm

Maybe ....I'm thinking that in my case being turbocharged and running boost near the limit or even above the efficiency range of my turbos, the moisture in the air is like water injection and the cooling effect of the latent heat of evaporation of water allows me to boost higher at the same outside air temperature or make more power at the same boost without the ECU pulling timing to retard knocking etc. But I'm not 100% sure that's right, I'm just sort of fantasizing that.

Wet air makes a noticable difference in pwer also - the water droplets vapourise and 18cm^3 of water converts to 22L of steam, so the extra expansion is huge.

I gotta say, humid air or cold air is really not going to affect the way your engine performs, unless you trick yourself into believing it will. Simply not enough change to warrant feeling it, unless of course an arctic crosswind is blowing into your intake at 30psi. Ha.

If you want to answer this question, look at any operating handbook for a small single engine airplane like a Cessna 152 or 172, or anything else without a turbocharger. On a twenty degree day, a 172 will lift off in about 600 feet. Same load on a 90 degree day, 1200 feet. Cooler air makes an engine perform far better than warm humid air. Aside from sucking gas in from the bottom and opposing cylinders, the engines are identical to the one in your old car.

It's not totally true that the shorter takeoff is due to just improved prformance of the engine - the wings work better in cold air because the density is higher, so the lift is higher.