Ok here's a dumb question.

[Stefan2k]

Ok what is the purpose of a cold air intake? i thought it was to get cooler air into the engine. the logic being that the cooler air is denser and expands more upon combustion giving more power.

So with that thought in mind, driving in colder temperatures should give the same effect as apposed to driving in a hotter temp.

Am I wrong? i have read many comments in these forums where people say they are getting worse gas mileage in cold weather, so what am i missing?

Am I to believe that I should get better gas mileage in 75 degree temps vs 30 degrees?

Metals conduct electricity better when they are cold so you should get a stronger spark, you only need the battery to start the car not run it. The engine is warm in what 5 minutes?

What am I missing?

 

[brittanyhale]

You kind of answered your own question, but I'll elaborate. 1) The increased air density caused more drag so you car must expend more fuel to overcome the resistance. Think diving into a pool of water versus a pool of air, the water slows you down more because it is more dense. 2) The tires may be under inflated for the same reason; as the density of the air increases, the volume must decrease. This is often demonstrated by inflating a ballon and placing it in the freezer. The balloon will shrink significantly in size. 3) increased idle time. If you are allowing your vehicle to warm up or defrost you are effective getting 0 miles/gal during that time, when that is averaged into your average miles/gal it can significantly reduce it. Hope this helps!

 

[Stew]

brittanyhale nailed it pretty good there, also all the oil and grease is thicker in the cold weather (engine oil until it's up to temp, trans oil, etc) needing more power to rotate stuff.

What a lot of hypermilers will do is make a warm air intake. The warm air is less dense meaning less fuel is needed to keep A/F stoichiometric.

 

[The Champ]

One of the biggest issues for reduced mileage that hasn't been mentioned is the fuel.

Winter fuel blends (yes, summer gas is different than winter gas) typically result in 1 - 3% less fuel mileage.

Another issue is the oil viscosity when cold. There is more resistance to flow when cold - so until the engine warms up, your oil provides more resistance that reduces fuel consumption.

A third item is wheel slippage on ice or snow covered roads. Every time you spin your wheels, it reduces fuel economy.

 

[Uncletom]

We bought an '06 PT Cruiser GT convertible a year or so ago. The previous owner had installed a lot of stuff on it including a loud blow off valve. {That's what sold the car to my wife}

They also put on a Borla exhaust and removed the catalytic converter and installed a 'cold air' filter thingy.

I don't know if these things improved anything at all. I did try a 'cold air' system on my HHR because it was given to me for free but all it did was increase the engine noise. NO better MPG or anything else.

I really did not think it would make any difference at all and I was right. 'They' tell me I need to get a different tune like a trifecta tune or something. I just took the 'cold air' setup off and sold it.

I am however thinking of getting something like this

http://www.ebay.com/itm/Polished-Al...ash=item4d3c32d4bf:g:5jwAAOSwnH1WXhh7&vxp=mtr

and installing it with a hole in the hood of the HHR to see if it might actually help some. My wife is convinced I would drown the engine when it rains. I don't know, I did have a functional air scoop on my '69 Mustang.

I really doubt it gave me any better MPG since it had a 428 Super Cobra Jet engine in it, but it was awesomely cool.

 

[Swordsmith]

Cold air is more dense. This does not give you more power because it expands more, it gives you more power because you can fit more air into the combustion chamber, and that means you can also put more fuel in and still get full combustion.

Combustion of fuel plus air results in an "explosion" (it's really just extremely rapid expansion), and the more of the two (assuming the ratio of the two remains constant) you have, the more power each combustion gives you.

Yes, this means you can have more power on a cold day than on a warm day. That power isn't free though, you have to add more fuel to get there. It really only happens at the top end of your throttle, too, if you are floored on a warm day (and your computer lets you have all the power available) you might only get 140hp, while the same engine on a cold day (again, without a tune that prevents this) might give you 145hp, because it can burn a little more gasoline. If you only need 50 hp, though, you'll use the same amount of fuel to make that, regardless of the weather.

Most of the things marketed as "cold air intakes" are actually warm air intakes, oddly; the Sonic comes, stock, with a cold air intake, as it draws air in from the fender, , while most of the intakes instead draw directly from the engine bay. A few, like MFab's build a sealed box to wall off engine heat and go back to drawing from the fender, while recommending removing the "snorkel". They get any power gains not by this cold air/hot air difference, but rather by being much less restrictive, so the engine isn't trying to breath through a soda straw.

As has been mentioned many times, though, the Sonic's stock tune will deny you almost all added power you could potentially be getting from cold air, or less restriction, etc; it's set up to give you X amount of power when you push the accelerator down X amount, no matter how much power your engine is capable of.