Has anyone ever seriously pondered the improvements that a cold air intake imposes on engine performance? Let's take out the friction, high flow filters, sound waves and air pressure factors. In the case of colder, denser outside air versus warm under-the-hood air, what are your opinions on it? To me the whole cold air is denser than warm and allows a higher number of O2 molecules into the combustion chamber thing made sense to me until I read these oil/MPG tips in another thread on here (http://www.lubedev.com/smartgas/quickies.htm). In one hint he states the warm air is better and that got me thinking: warm air has a higher energy level than cold air, hence cold air has less kinetic energy making it more dense. Anyone whose taken general chemistry knows that if the oxygen molecules are excited enough they don't need as much energy to initiate a reaction. My logic tells me that warmer air needs less energy from the spark plugs to cause a redox reaction with the gasoline, therefore making warmer air more efficient in NA set-ups with close to stock timing... I was bored and that's just my $0.02... feel free to bash me.

 

Unless you have a turbo or supercharger, air is drawn, not forced,into the cylinder during the intake stroke. The piston moves down, creating a low-pressure area ("vacuum") relative to whatever the air pressure is in the air intake line to the engine. Air moves from higher pressure to lower pressure, so the cylinder fills with the air/fuel mix.

The ensuing compression stroke then takes place and the compressedmixture is ignitedat the beginning ofthe power stroke.

Then the combustion products are ejected during the exhaust stoke and the O2 sensor outputs data to a computerso that the proper amount of fuel is added orsubtractedby the fuelinjection system.

Equal volumes of warm air and cold air can be at the same pressure, so you can fill the cylinder with either warm summer air or very cold winter air.

Very cold winter air is more dense (more molecules per unit volume) thanvery hot summer air.

More molecules of air in the cylinder means that more molecules of fuel can be added to it and still have an efficient burn.

More fuel means more energy released during the burn and, therefore, more power in the stroke.

Although it takes some small amount of energy to heat the intake air just before and during combustion, it is far less than that gained by usingmore air molecules plus more fuelin the mixture.

I think it would be a relatively easy matter to determine which air temperature allows an engine to produce more power in a fuel-injected car.(If that is the goal we want to achieve here.) Put the car onan outdoordyno when the ambient air temperature is 110 and then do the same when the outside temp is -25. With the oils in the engine and transmissionat normal operating temperature, I think the engine will produce more power at -25.

 

from personal experiences... cars, at the track, go faster and have the best et's in cooler, more dense air.

it would beeasy enough to test. have a shop bend some pipe to place a filter behind the radiator (where the hottest air would be found,besides off the exhaust). run a few tanks of gas through it. then install the cai and fill 'er up, and check mpg again.

i think this is the more convinient way to check efficiency... unless you have a dyno in your garage.


edit: i think tony's ideas good too lol.

 

well i think if the air is colder you putting more molcules into the engine, Becuase the cold air is more compressed. If the air is hot then the molcuases are seprated out and less is being sucked in.

 

Those are all very good points and I agree with all of them, except whether my car runs better at -25 than 110. I know for fact that my car performs and responds much better in 75º, 85% humidity than the cold 20º, ~30% winter condition here in Minnesota. More evidence of this is that I get worse MPG in the winter with more relaxed and conservative driving than my pedal mashing summer driving. I encourage you all to read this article about activation energy: http://en.wikipedia.org/wiki/Activation_energy.

This brings me back to my chemistry point: Warm air is already close to reacting with gas and the spark plug provides a big enough spark to initiate (add the required activation energy) to the mixture to bring all of the molecules to reaction more efficiently and simultaneously.

Also, if you think outside air @ -25º is still at -25º in the combustion chamber, you are way wrong. With the low specific heat capacity of aluminum in the intake tubing and the temperature of the intake manifold and engine block the air is already at least 75º or so. Thats one of the reason N2O works so well; when injected that close to the combustion chamber it can reduce air temps that low and coupled with the extra oxygen it provides produces more power.

 

You're more thanlikely getting worse mpg during the winter because you're driving a more powerful car at all speedsduring the winter. That is why I qualified my statement that what we want here is more power rather than greater efficiency (higher mileage).

More availiable horsepower is a lot less fun during a Minnesota or Alberta winter, however.

No one would eversay that an outside air temperature of -25 would mean that the air temperature in the cylinder would be -25. However, I think it is more thanreasonable to conclude that the air in the cylinder on a day when theambient air temperatureis -25would be much colder than theair in the cylinder when the ambient air temperature is 110 - possibly by as much as their ambient difference, but both certainlybeing raised by the hot surfaces they touch.

Practically speaking, if warm air+fuel provided more power than cold air+more fuel, there would be hot-air intakes on the market rather than cold-air intakes. Such a fact would have been noticed by horsepower-seekerslong long ago.

 

I agree with the hot-air intakes, but take a look at the whole aftermarket part industry and compare claimed vs. actual gains. Half the problem is most likely false advertising. You always sell more if you exaggerate what the product does. I think it would be interesting to test the parameters in a completely controlled environment, but then again any real gains made would unpractical in a normal scenario with changing conditions.