why Warm intake?
 

with every car I know a warmer intake air temp actually chokes the engine, causes misfires, over heating, decreased efficiency, and many other bad things. (usually referred to as heat soak)

so why do you guys close off all heat dissipation holes, and use warm intakes?

in high performance engines heat dissipation is usually used for better efficiency, and it was noted that fire burns more efficiently with cooler surrounding air.

warmer engine bay and hot intake air sounds bad and puzzles me.
Im pretty sure heat soak negatively affects MPG

ok don't answer this the WAI work differently on American made engines and older engines.
i was just confused because an extra o2 molecule is always better thats why No2 works so well for power improvements. :D

metalshark -

(I'll give it a try, but others can describe it better than me)

The idea is the opposite of the Cold Air Intake (CAI). The idea with CAI, as I understand it, is that the colder air is supposed to be more dense ("heavier"?!?!?), so it has more oxygen by volume. The car's ECU/PCM sees more oxygen in the exhaust (02 sensor) and therefore adds more fuel to maintain the 14.7 stoichiometric Air/Fuel Ratio (AFR). The added fuel is a "richer" mixture that increases HP.

The idea with the Warm Air Intake is just the opposite. The hotter drier air has less oxygen in it. Based on the above rule, the AFR is leaned out. It's like driving on a hot dry day in the desert (without the overheating part, ;) ). It's a way to trick the ECU/PCM into leaning out the air/fuel mixture.

This concept has been used by Honda Insight owners in the winter months to maintain good MPG.

Distinction: In high performance applications, the way the engine is being used is different than eco-hypermiling applications. In high performance, then engine needs cooling because it is being used to it's limit. In eco-hypermiling, the engine is most often *not* being pushed to the limit. It is safe to "keep the heat in" because the engine isn't being driven to the limits of it's performance envelope.

Does that make sense?

CarloSW2

metalshark -

PS - It is very drivetrain specific. Some car ECU/PCMs like it, others don't.

Sometimes you feel like a nut, sometimes you don't,

CarloSW2

To look at it from a slightly different angle -

Forget the O2 sensor(s) for a moment. Think about the fixed-diameter intake path. CAI helps because the denser air allows more oxygen molecules through that path. WAI will allow fewer. But then we're not looking for max HP.

So likely benefits are reduced intake turbulence and aero resistance in that path due to less dense air. I think that's also called pumping losses. The gas miser's engine is usually running at low throttle so being able to run at slightly wider throttle for the same amount of O2 gives less pumping losses.

Also I think WAI gives easier/more thorough combustion due to the warmer temp.

Back to the O2 sensor. The feedback loop will do a good job ensuring that the actual air/fuel ratio stays at the designed value. So it really doesn't matter too much what temp air you put in, at least as far as the O2 sensor is concerned. Intake Air Mass Sensors are a different story. I think different types respond to air temp changes differently. But since the O2 sensor has the last word in managing the air/fuel ratio, I don't think it matters much unless you have the old Bosch/Volvo type intake sensor that is damaged by hot air.

All the conditions you stated happen under high loads.

Because most of the driving is done at light loads.

Performance, not efficiency.

It depends on your driving behavior, and also your engine specifics.

Best case scenario you'd have a vacuum actuated flap connected to the intake manifold so when you jump on it you get cold air in, but warm air when cruising.

Also note a warm air intake is counter productive in regards to power and efficiency on a diesel.

warm intake
 

Many good comments already.Here's my two cents.The majority of auto emissions occur within the first few minutes of a "cold-start." The warm-air intake attempts to aid fuel vaporization during this warm-up period,reducing hydrocarbon emissions ( VOCs and CO ).Once up to operating temp,a temperature-controlled bypass-valve modulates intake charge temp to balance between charge-density ( horsepower ) and complete combustion ( emmissions ).GM/SAAB places an electrically-heated plate ahead of each intake port of the cylinder head to accomplish this cold-start emissions abatement.

Only unburned hydrocarbon carbon monoxide emissions and are high at start up. Nox emissions are low at this time. Once things warm up hydrocarbon emissions and carbon monoxide drop and Nox emissions rise. A warm air intake will drop hydro carbon emissions a little and increase Nox emissions a lot.

Do you have anything to back this statement? How much do you think 100 F higher IAT raises the combustion temperature? Were you talking about just the warm up phase?