ambient air temp vs. power

Do I really need an intercooler when it is -10F? If a cold air intake can add power, I guess I had lots on tap this morning.

I did wonder on my drive in this morning what the sweet spot is. As ambient air temp goes down and the intake air is thus cooler and more dense the engine could develop more power, but I figure with the colder temps, there is more parasitic drag from the thicker grease in things like wheel bearings and other similar items. What temp does a car produce the most power? Opinions or facts or even opinions masquerading as facts are all acceptable.

The ideal situation is using a water-to-air intercooler and filling the reservoir with ice. That way your intake charge is super-cool, but the things that need to stay warm (e.g. tires) actually stay warm.

I think the temperature you're looking for is far below the point where it matters. I know in the morning at Roebling, the Fiesta would hit ~117 indicated speed at the end of the front straight, a good 5 mph advantage over the afternoon. In the morning, it was something like 35 or 40 degrees. If it gets much colder than that, your limiting factor will likely be the ability to put the extra power to the ground rather than the parasitic loss of cold grease. Wheel bearings, transmissions and the like come up to temperature pretty quick. Tires in contact with ice-cold asphalt, on the other hand, is another story.

Your charge temp will still be just as hot without an intercooler, the difference between frosty winter temps and hot summer temps means little after the air passes through a searing hot turbocharger and then straight through some low-surface-area pipes to the intake...which will also be quite hot.

An intercooler on the other hand would let you really take advantage of the lower ambient temps.

And +1 on not worrying about grease temps etc. The only things on your car that won't be plenty hot enough real quick are the tires, the engine operating temp (no way around it without some kind of engine heater), and possibly the brake pads.

It all seems to average out through the seasons. Winter, more power, more drag, more fuel. Summer, opposite of above.

I have gone through all of this for tracking weather at the track using basic inputs (Temp, Humidity and Barometric pressure). Here is a quick list of computation to find the Relative HP mulitpier for given conditions:
StdBaroInches = 29.8
Inches2mb = 33.86389
Baro_mb = Barometer * Inches2mb
StdBaro_mb = StdBaroInches * Inches2mb
StdTemp = 85
StdTempK = ((StdTemp - 32) / 1.8) + 273.15
TempC = (Temp - 32) / 1.8
TempK = ((Temp - 32) / 1.8) + 273.15
SatVapPres = 6.1078 * 10 ^ ((7.5 * TempC) / (237.3 + TempC))
VapPres = (Humidity / 100) * SatVapPres
RelHp = 100 / ((1.18 * (StdBaro_mb / (Baro_mb - VapPres)) * ((TempK / StdTempK) ^ 0.5)) - 0.18)
All you have to do now is some quick calculations and voila you have the realtive power assuming all other variables (engine temps, grip level of tires, etc are the same). Most of this comes from an SAE specification that I don't recall the number for...
I included this with a weather logging system and found that that 'Happy Hour' practice at Indy usually has the best power to drag ratio (again all other things being constant, and they are not).

It really depends on how the car is setup to take advantage (or freak out) of the changing conditions.

Turbo cars tend to like cold air. Partially because of the potential for cooler charge temps, but i believe (someone correct me) mostly because of the denser air means you're getting more "mass" taken in.

Using the MX6 as an example, it doesn't measure mass, it measures velocity. Velocity will largely stay the same no matter what temperature or density of the air, so what you run into is a "lean is mean" scenario where up to a point, the car will make a LOT, and i mean a LOT more power in cooler temperatures.

The difference between 90 degrees and say... 45-50 degrees in that car is staggering.

But, in 0 degree weather, it's not so good, because now we've gone so far that the ecu is freaking out.

Assuming you're not just doing dyno pulls outside in the middle of winter, remember that your car also has to move through the denser, heavier cold air, taking more HP to do so.

Thats a whole different set of calculations...
Got 'em if you need 'em...

Swank Force One wrote: Turbo cars tend to like cold air. Partially because of the potential for cooler charge temps, but i believe (someone correct me) mostly because of the denser air means you're getting more "mass" taken in.

Yeah it's really all about the mass, lower temps are just a means to that end. A cooler charge means you can get more boost without putting as much energy into the turbocharger. The only advantage of coldness in and of itself is that it reduces pinging/detonation.