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Do cold air intakes give you better gas mileage?

Originally posted by: Gobadgrs
http://www.knfilters.com/cold_air_intakes.htm

Excuse my ignorance, but if you're getting more air into the engine, wouldn't that thin out the mix and make it leaner, resulting in better mileage?
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No, just about every EFI car is metering air on its way in, including density, and adding fuel to maintain the A/R that the ECU wants to keep.

The idea behind a cold air intake is that they'll bring in denser air, so you'll be able to burn more fuel per stroke, meaning more power at a given load, if I understand it correctly. I'm not sure if that helps or hurts fuel economy, but I think the mileage claims are based mostly from a "less restrictive" intake so that less energy is lost in creating intake vacuum (when the pistons go down on the intake stroke).

Could be a combination of the two, but I'm pretty sure leaning out the mixture is not how they help fuel economy. That said, you're not going to see big MPG gains from a freer flowing intake. I wouldn't advise spending the money on one if you have a stock car, since the stock intake is probably not too restrictive at those air flow levels. If you're running 20PSI out of a T88, you might need a big purple cone filter.
 
Probably lower mileage. ECU should maintain constant fuel to air mixture, so colder air will result in more fuel being injected. One reason why my mileage drops during winter.
 
Originally posted by: senseamp
Probably lower mileage. ECU should maintain constant fuel to air mixture, so colder air will result in more fuel being injected. One reason why my mileage drops during winter.
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Well that and the winter gas mix they use with more ethanol.
 
I didn't do a before and after on my intake, but since adding my header, cat and exhaust my mileage has seemed to improve.

It's only been a couple tanks so far...I am continuing to watch it.
 
Originally posted by: senseamp
Probably lower mileage. ECU should maintain constant fuel to air mixture, so colder air will result in more fuel being injected. One reason why my mileage drops during winter.
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Sounds about right.
 
Originally posted by: alkemyst
I didn't do a before and after on my intake, but since adding my header, cat and exhaust my mileage has seemed to improve.

It's only been a couple tanks so far...I am continuing to watch it.
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Header and exhaust will improve efficiency by reducing back pressure and power loss during the exhaust stroke. A cold air intake, as others have said, allows the engine to burn more fuel due to the denser air, thus reducing fuel economy (though I doubt the difference is even noticeable)
 
Cold air intake, headers and exhaust will generally reduce fuel efficiency. This is because they don't affect frictional losses inside an engine, but they do increase pumping losses. Because they allow an engine to generate more power at the same conditions (engine rpm + throttle position), the throttle will be closed more than otherwise, increasing pumping losses.

This runs counter to what many engine designers are trying to do these days to increase engine efficiency. You decrease the max power output of the engine, allowing for a larger throttle opening and reduce pumping losses. Any variable displacement technology (where cylinders are deactivated), and atkinson cycle operation (for example in the toyota prius or the honda civic's r18) work in this manner.
 
Originally posted by: Dman877
Originally posted by: alkemyst
I didn't do a before and after on my intake, but since adding my header, cat and exhaust my mileage has seemed to improve.

It's only been a couple tanks so far...I am continuing to watch it.
Click to expand...

Header and exhaust will improve efficiency by reducing back pressure and power loss during the exhaust stroke. A cold air intake, as others have said, allows the engine to burn more fuel due to the denser air, thus reducing fuel economy (though I doubt the difference is even noticeable)
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It depends on the exhaust. To put it simply, backpressure is a important measure of how much torque you're creating at low to mid rpms which is why all cars don't just have a 4" exhaust back from the cat.

Now horsepower is a function of torque and yes, too much low can decrease power. A equal length header followed by 4 piping with no cat on a 4 cylinder car will probably make you lose hp and torque cross the board.

If you want to create better mileage, you want more torque down low so you don't have to bring the engine as high up to get it moving and you can stay in higher gears longer.

What you're seeing is instead the switch from winter blend fuel to summer fuels. During winter months, you probably get a 85/15% blend of ethanol and gasoline, which means you're only getting 94.75% of the total energy content hat you'd get from a gallon of 100% gasoline.


As for the OP, intakes won't noticeably improve anything besides making the "whoosh" intake noise louder. Power will be affected minimally and mileage will not go anywhere in any measurable amount.
 
Originally posted by: alkemyst
I didn't do a before and after on my intake, but since adding my header, cat and exhaust my mileage has seemed to improve.

It's only been a couple tanks so far...I am continuing to watch it.
Click to expand...

The increase is because of your exhaust. Stock exhaust systems are fairly restrictive, by freeing up the exhaust (making it easier on the engine to expel the exhaust) you are putting less load on the engine thus making it more efficient.
 
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