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Was working under the hood of my Civic, checking the oil and the like. I noticed that the air intake (http://www.biased.org/misc/cars/Nellie/piccyfix_1237077696_07032009(001).jpg) for the Civic was as far away from the engine as possible but on my old Nova, the main air intake (http://www.biased.org/misc/cars/Snap/p3160958a.jpg) is fairly near the engine. There is a short pipe from the exhaust manifold heat shield to the bottom of the air intake tube and there is a hole in the heat shield so warm air would flow into the air filter. The pipe is directly under the large black blob (the one with a thin red hose leading away from it). This pipe is not visible in the picture This seems to me that Honda is trying to get the air entering the engine as cold as possible, and Vauxhall (GM) is trying to get a mixture of warm and cold air entering the engine. What's the rationale behind this? Is it because Honda wants the best performance out of the engine (as absurd as that sounds...) and Vauxhall wants the best fuel economy out of the engine? Would it help the Honda engine to get better FE if the air intake had warmer air from the engine? Or would the difference be so slight, it doesn't matter?

On older cars, I believe the pipe bringing warm air to the intake is used only when the engine is cold. As the engine warms up, a vacuum-actuated damper closes off the warm air and opens the cold air into the air cleaner.
The "black blob" with the red hose is the vacuum actuator in your picture.
In newer cars, I believe they bring in colder air to help the engine make more power.

Someone please correct me if I'm wrong.

The Fridge is exactly right.

Warm air is FE

Cold air is performance

The vacuum control is actuated when you put your foot down, giving cold air when under load, and hot when cruising.

I think.

I would mod your intake and find hot air for economy, as I get around 10% better FE with hot air.

Too cold intake temps can ruin lean burn on the civic and really drop FE

I have a problem with the "warm air is FE" explanation.

If cold air is performance then it increases the power of the engine making acceleration take LESS throttle pedal for the same performance and therefore better FE.

If you use the cold airs improved performance to get improved performance, then, yes, FE goes down. But if you use the ability to have a lighter foot for the "same" performance then you get improved FE.

I can see NO way that warm air would improve FE since the lowered performance would require MORE accelerator pedal to get back to where you were before the modification.

ALSO, the O2 sensor (s) that help determine the amount of fuel injected will compensate for what ever changes you make at the intake.

Unless you live in cold country...I dont...where the engine may increase the fuel intake because of temperatures below 60F, then cold air intake is better,

Hi Jim:

___You can see it in your Insight if its the 5-speed with and w/out a WAI mod attached. Cold temp locations is what it is all about. If you have IAT's in the 75 + range, you will never have to worry about it. When AIT's are in the -10 to 60 range, it makes a difference.

___Good Luck

___Wayne

It seems to me, that is what I just said....right?

Only in winter or in high latitudes will it be advantages to use a warm air intake. Because it gets the car warmer faster thus reducing fuel burn. But once warm, the warm air intake should be modified....just like they did in the old days with the exhaust riser that cut off after the engine was warm. A permanent warm air intake is counter productive.

Where I live, temperatures, even at night, are rarely below 60F. This past four days they have been, but tomorrow they wont be.

In the *absence* of a lean-burn system and with modern closed-loop
control, incoming air temp makes much less difference than it
may have in earlier systems. I tried my car with and without
various instances of WAI over the past few winters; this winter
I just left it off and if anything my MPG was slightly *better*.
Probably due to learning yet more technique tricks, but my overall
observation has been that the WAI does very little for the Prius
other than feeding the production of several silly webpages.
.
_H*

In my Insight I have found this to be true as well.

If cold air is performance then it increases the power of the engine making acceleration take LESS throttle pedal for the same performance and therefore better FE.


You do realize that your throttle does not control how much gas goes into your engine right? You only control the throttle body, and your car's computer figures out the rest.

With warm air, you're using more throttle to achieve the same power.
With cold air, you're using less throttle to achieve the same power.

Less throttle means the butterfly valve in the throttle is more closed. It takes more work to suck air through the more restricted opening. Lower FE is the result.

Warm air also helps speed the warmup phase. Depending on how long your drive is, this can make a significant difference. Remember that to the engine that operates in the 180+ degrees range, even 60 degrees is cold.

Yes and NO. If the throttle is NOT opened then the computer thinks you dont need to go faster and the amount of fuel and air will be decreased. The opposite is also true. Of course there are other factors that also feed into the computer to help it decide on the amount of the fuel....as I noted previously....the O2 sensor detects the lack of complete burning in the exhaust and influences fuel quantity at the intake.

BUT the bottom line is, Open throttle more fuel, closed throttle, less fuel. And that all makes sense since acceleration = open throttle = more energy required = more fuel = acceleration = open throttle .....etc....etc.... They are all linked. You cant go faster without more energy...either through more fuel OR better extraction of energy from the fuel already present. YOU NEED MORE ENERGY...from somewhere. If cold air allows more fuel in and the engine efficiency is NOT changed then more energy will be produced and the car will go faster...OR...you will relax the pressure on the throttle and keep it at the same speed by reducing the amount of fuel introduced.

Its simple, but it is basic physics.

Warm air is more efficient. It expands. Gasoline vapors are less condensed within the intake, since the spark is not changed the fuel burn is more complete, leaving less unburned fuel to exit the exhaust manifold. It's strength is efficiency not power.

Think about the smell of fuel at a dragstrip, that is excess fuel coming out the exhaust, maximum power, maximum waste. With every conceivable manner of cold air induction, nitrous oxide under tremendous pressure at 900lbs per square inch, blowers, intercooled turbos, CAI's, chilled intake manifolds etc.

Sometimes a commuter car will appear to have better fuel economy with a CAI, this is because it is producing more power and the driver is handling that increased power efficiently. Longer glides, less pedal.

If the same car was dyno tuned with a good WAI system for the purpose of economy it would use less fuel (good), produce less power (not necessary for hypermiling), exhaust less wasteful unburned fuel (good) and have a lower top end (not necessary for hypermiling).

Oh, don't think this way of thinking goes over well with true hardcore build for speed engine shops, they can't get comfortable with the combinations of warm air, high compression, water injection and lean vapor burn, it is hard to make sense because it is against everything they have been taught or have experienced. - Dale

What's the rationale behind this? Is it because Honda wants the best performance out of the engine (as absurd as that sounds...) and Vauxhall wants the best fuel economy out of the engine?

I think the answer is tied into the age of the vehicle. The Honda uses a modern EGR system - Exhuast Gas Recirculation - to add warm exhaust air into the intake for warmup. This helps emissions, and I believe the cold air intake balances the heat. You should see the snorkle on my Nissan. It points forward right behind the headlight.

Warm air is less dense. That means less oxygen in the cylinder. The O2 sensor reports this back to the computer. The computer reduces the fuel supply to maintain the optimum air-fuel ratio.

Basically, a warm intake makes it act like a smaller engine. A cold intake is like a larger engine.

Andrew and Dale are both right on target:

One point that needs to be added however, is that the effect of warm air vs. cold air also depends on whether you have a MAF or MAP sensor. A MAF sensor goes by the actual amount of air coming in to adjust the air/fuel ratio, my map sensor goes by the manifold "vacuum" to determine the ratio.

Determination by a MAF sensor, warm air is less dense, so less air is flowing, so the computer injects less fuel, simulating a smaller displacement. Of course it doesn't do this depending solely on the MAF sensor as the 02 sensors and emissions have to comply to a certain extent and excess fuel needs to be burnt. The more fuel injected, the more unburnt fuel you have. There will always be unburnt fuel in the exhaust. Efficiency of the ICE is not 100% as far as combustion is concerned.

Determination by a Map sensor is vacuum in the intake manifold. Using this vacuum or negative pressure, combined with the 02 sensors, the computer determines how much fuel to inject to promote combustion as close to 100% as possible. The less fuel that ends up in the exhaust, the better it is for fuel economy.

The cooler your engine is specified to run, the less energy from the gasoline gets dissipated as heat, the leaner it goes with warmer air. Heat is an engine killer so most engines want to be run as cool as possible. Think of this as a boundary layer problem. As air temps increase, within a certain boundary, less fuel is injected to keep engine temps lower to reduce NOx emissions...and also to extend engine life.

I think the answer is tied into the age of the vehicle. The Honda uses a modern EGR system - Exhuast Gas Recirculation - to add warm exhaust air into the intake for warmup. This helps emissions, and I believe the cold air intake balances the heat. You should see the snorkle on my Nissan. It points forward right behind the headlight.

Oh yeah of course. EGR. That makes a lot more sense. My old Nova didn't have an EGR system.