Cold air VS Warm Air Intakes - what's the difference?

[deadman1474]

What are the advantages of a warm air intake over a cold air intake? I know that I have always seen cold air intakes as being for performance/ Efficancy. Your thoughts

[MetroMPG]

Cold air has more oxygen by volume. So you can stuff more fuel into the cylinder while maintaining the proper air/fuel ratio. That's one reason why the go-fast people like it.

The idea behind using warm air for efficiency is to intentionally depower the motor. Less oxygen by volume means you must open the throttle further to generate a given amount of power. A wider throttle opening means reduced pumping losses.

BTW, the O2 sensor will always strive to maintain the proper air/fuel ratio, so it's not running lean.

In a way, it's similar to driving at high elevations (less O2 in the air), which can be more efficient for a number of reasons.

In practice though, whether it works seems to depend on the specific vehicle and how it's programmed to respond (or not) to the increased air temps. Some ECU's may back off timing to prevent knock, so you end up with a zero gain. The Saturn drivers seem to have good luck with it though.

[deadman1474]

Originally Posted by MetroMPG

Cold air has more oxygen by volume. So you can stuff more fuel into the cylinder while maintaining the proper air/fuel ratio. That's one reason why the go-fast people like it.

The idea behind using warm air for efficiency is to intentionally depower the motor. Less oxygen by volume means you must open the throttle further to generate a given amount of power. A wider throttle opening means reduced pumping losses.

BTW, the O2 sensor will always strive to maintain the proper air/fuel ratio, so it's not running lean.

In a way, it's similar to driving at high elevations (less O2 in the air), which can be more efficient for a number of reasons.

In practice though, whether it works seems to depend on the specific vehicle and how it's programmed to respond (or not) to the increased air temps. Some ECU's may back off timing to prevent knock, so you end up with a zero gain. The Saturn drivers seem to have good luck with it though.

Thanks I always wondered about it.

[Beaver]

I understand that cold air is denser and contains more oxygen by volume than warm air, but the reason for depowering the motor I don't quite get. Maybe if you can explain what you mean by "pumping losses" I'll begin to get it. I was under the impression that under steady state circumstances the motor produced the amount of power required to maintain the steady state (say 55mph on a flat freeway with zero wind). Regardless of the amount of power the engine is capable of producing, it only actually produces the amount of power required of it at the time. I was also under the impression that the amount of power produced by an engine, all other things being equal, was proportional to the difference in the temperature of the air/fuel mixture entering the combustion chamber vs. the temperature of the combusted air/fuel mixture (exhaust) leaving the combustion chamber. The temperature difference would be greater if you start with a colder air/fuel mixture. Wouldn't this mean that with cold intake air the engine would not have to work so hard to power the car? This being the case, could you have a smaller engine or a smaller carburetor/throttle body and still get sufficient power for your needs? In the end, wouldn't this result in better economy?
I don't mean to be argumentative, but I'd like to understand. I come from a hotrodding background and it always seemed that a cold air intake was a cheap way to increase performance without suffering other ill effects, such as poor economy from a performance cam or a big carb. It seems that some of the performance tricks work okay for economy (free-flowing exhaust, aerodynamic mods, etc.) but others don't. Sometimes the differences are obvious (hot cams come to mind) but I don't get the cold air thing. Enlighten me please.
Thanks!

[RH77]

I have a brief response -- incomplete answer.

From the shop manual on my vehicle, the engine is intended to run richer at intake temperatures below a certain figure (I forget the exact number, let's say 60F). Warm air is needed to satisfy this requirement, especially in Winter.

Beyond that, I've determined with repeated testing that my engine operates most efficiently with IATs at 90-100F. Beyond 120-130F, it starts to dump-in more fuel to compensate for pre-ignition, and fools with the timing. So that temp above the maximum requirement of ambient up to at least ~90F yielded around a 15% increase when I first tested it 2 years ago (the abstract is floating around somewhere -- I think there was a cold-air intake on the car before). FE drops when colder air is introduced, even at ~70F, which is well within the requirements of the sensor/ECU closed-loop management. You may find terms of HAI and WAI (hot and warm air intakes).

How it works -- not exactly certain. A couple years ago I did quite a bit of testing with different temps and found the "sweet spot" for my car. There's still quite a bit of discussion on the topic and the term "pumping losses" can best be explained by someone with more Physics knowledge than I have.

My advice? Experiment yourself with different temps -- and stay as Scientific and consistent as possible. See if you can obtain info on IATs and the vehicle ECU's compensation from a shop manual or enthusiast website. BTW, what kind of vehicle do you have?

Let us know if you test and come to some conclusions.

RH77

[trebuchet03]

^^

The quick and gritty explanation....

Reduce vacuum and you reduce pumping losses.... There's plenty of products out there to reduce intake restriction - but they overlook one point... The throttle plate is the biggest freaking restriction in the whole line

The temperature difference would be greater if you start with a colder air/fuel mixture. Wouldn't this mean that with cold intake air the engine would not have to work so hard to power the car?

Heat rejection temperature (hot side of a heat engine) isn't static... Start with fluid temp - add X heat - you'll end with Y fluid temp.... Increase initial fluid temp - add X heat - you'll get Y +Z fluid temp That's an oversimplification - but the key point is: max temperature doesn't remain constant

Perhaps it's nit picky - but if you're generating the same amount of power over the same amount of time.... The amount of work generated is exactly equal

[MetroMPG]

Having said all that, when I tested cold (~55 F) vs. warm (~116 F) intake air @ 39 F ambient with my car, it made no significant difference. No gains or losses:



Details: http://metrompg.com/posts/wai-test.htm

Not saying this will be the case for every vehicle. Also, my testing of this mod wasn't ideal (no additional set of "A" data).

As with much in life, "it depends."

[Beaver]

Okay, it's starting to make a little more sense now... The ECU is overthinking the situation and correcting for what it sees as problems. If the computer didn't do so many "favors" for us we might be able to tweak our engines more for better economy. Maybe not. Maybe I'm just too "old school." Generally it seems like the computer does a pretty good job of keeping the mixture in a reasonably good range most of the time; a lot better than most old carburetors did. But like most car design features, it is a compromise for the average driver under average conditions.

I'm not an average driver, and I'm guessing you're not either. It looks like, as you suggested, I'll have to figure out what the computer likes best and then try to duplicate that condition. Still, I'd like to be able to adjust the computer for what I think it should do, and then verify it myself. (I plan to get one of those cool Scan Gauge II's).

I think your advice is right, considering things as they are. I'll have to test to find out what intake air temperature works best for economy and try to provide that to the intake air sensor. Maybe at some point I can figure out how to trick the sensor and get colder air into the engine without the computer knowing about it, and see what that does...

Thanks for the explanation, and if I try anything along those lines I'll post the results on the forums here.

BTW, I will be driving a 96 Metro 2dr HB base model. No options, 3cyl 5spd. So far I have put less than 5 miles on it in the week that I've had it; I drive very little; mostly I am on foot. It runs kind of rough; I don't know if that's typical for a 3cyl or what. (any ideas?) I am mainly concerned with saving gas for geopolitical and environmental reasons, so it wouldn't make much sense for me to drive the car just for fuel economy testing purposes. That said, I won't give up my autocrossing so easily... Fo that I have a factory stock 98 Neon ACR (American Club Racer version). It actually gets decent mileage considering it has lower gears (3.94 final drive) than the standard models (3.55). It's a 2.0 liter DOHC, with few options so it is fairly light.

[Beaver]

Okay, the EGT not being static, but rather increasing along with intake air temp gives me more to chew on. And the Firefly charts are most helpful; they would probably apply almost directly to my Metro. Basically what I read then, is that I can leave the air horn running out through the front bulkhead, as is the stock configuration, and it won't help or hurt my mpg, though it may give me more hp at wot. Right? It may lower my egt and combustion chamber temps however, perhaps allowing me to run slightly more timing advance or use a lower grade of gas.

I can't thank you guys enough for your thoughtful and informed input! And I like the idea of not doing anything at all; inertia is my specialty. I just love to leave well enough alone every chance I get.
Cheers!

[oldschool]

The cold air vs warm air issue will be more of a factor in carbed engines, then in FI engines, and again more of an issue in outside temps below 50 degrees F. In carbed engines cold air may even present drivability issues in extremely cold climates.

On a carbed engine , hot air allows the engine to run a leaner air/fuel mix, as the hot air tends to allow more fuel vaporization, and less of a need for the combustion chamber to use the actual burn in converting raw fuel into vapor , or useable fuel. Deterents to this process are the fact that the air and fuel mixed past the carb rarely spend more then .6 seconds in the intake before entering the combustion chamber,(hardly enough time to cause an appreciablle change of state in the fuel).

Hot air on an FI engine could easily help if the fuel is also heated,particularly on a wet manifold system or TBI, and this is doable because of the increased fuel pressure before the line, that will inhibit vapor lock. When the hot fuel is introduced to the air stream, the hot air will further help to keep it in a close to vaporous state as long as the puter does nothing to dump extra fuel into the mix.

Systems using hot air tend to run in a smoother fashion again because the air/ fuel mix is normally more homogenous.