cold air=less mpg?

digitaldrifter91 · Feb 10, 2004

id like to ask, will colder air give you less miles per gallon? the reason i asked was that i converted my stock air box system to a cold air by blocking the holes for the fresh air inside the engine, and then in the resignator where the 3rd and 4th pipe went in the bumper, i cut a 4 inch hole to supply air. now in the bumper its just no heat, only the air outside whatever it is.

side note: the filter is still in its place

is there any drawbacks in tearms of miles per gallon? i feel a slight gain around 3-4400 rpm in my power band.

i have a 1991 honda accord ex with 160k

thanks.

SteveD2 · Feb 10, 2004

No, if anything it should increase it. Technically it will use slightly more gas, however, it also means the throttle doesn't need to be open as far to go the same speed. If hot air gave you better MPG, manufacturers would go out of their way to heat up the incoming air to satisfy the EPA.

Chris B. · Feb 10, 2004

Then why do you get worse MPG in the winter when it is always cold out?

47HO · Feb 10, 2004

quote:

i feel a slight gain around 3-4400 rpm in my power band

I think it may be your foot hurting your gas mileage!

Bob Woods · Feb 10, 2004

Then why do you get worse MPG in the winter when it is always cold out?

Because cold air is more dense air and creates more drag.

Shannow · Feb 10, 2004

If you've got a carb, then cold air will hurt mileage. If it's injected, then it should have little to no effect.

Increased fuel consumption in the cold can be a couple of reasons :
* longer warm-ups, relying more on cold start enrichment.
* prolonged idling to maintain the heater.
* gasoline that has been doctored for less emissions in winter.

N2OIL · Feb 10, 2004

Carbs in the cold your choke plate stays closed longer. Also on injected cars until your water temp gets to a good temp to signify it is warm say 180-190f then it runs on a rich fuel curve.
So if you have a bad thermostat or in the winter takes much longer to get off the cold curve. The bad fuel economy is richer fuel mixture.

digitaldrifter91 · Feb 10, 2004

i thought cold makes the air fuel ratio richer...

well mine is fuel injected. lol maybe its my foot on the gas, but really if i normally accelerate or slightly step on the pedal before and after my cold air setup then i feel more thrust in power. haha the butt dyno!

i think in winter everyone gets lower gas milage...i do all the time..haha.

its hard for me to tell if my mpg is more or less...humm..

S2000driver · Feb 10, 2004

From the laws of thermodynamics, the bigger the difference between the intake temperature and the exhaust temperature the more efficiency you can have.

The most significant reason for poor fuel economy is the ineffieciencies of the engine during warmup. The second most significant reason is that there is less energy in winter blends of gasoline. Anything else is trivial.

Shannow · Feb 10, 2004

S2000, I disagree that the greater difference between inlet and exhaust temperatures means better efficiency.

Hottest exhaust temperatures will be obtained from a blowtorch, with zero thermal efficiency, as no work is extracted.

Rick in PA · Feb 10, 2004

I can think of a few other things that contribute to lower gas mileage in winter. All lubricants thicken, motor oil, transmission fluid, constant velocity joint grease, grease in the bearings... The rubber in the tires is stiffer. Once the car is fully warmed-up, these do not impact mileage but untill the car is warmed-up it's all parasitic loss and contributes to lower efficiency. The more short trips you do, the more these parasitic losses contribute to lower average gas mileage.

digitaldrifter91 · Feb 10, 2004

well without talking about winter and stuff...hehe thats all im looking for, cold air =less mpg...but true winter does count for many things...crap =)...summer i got 300 to the tank, now i get like 270
i guess i need to do some research on this tonight.

SteveD2 · Feb 10, 2004

quote:

Originally posted by digitaldrifter91:
well without talking about winter and stuff...hehe thats all im looking for, cold air =less mpg...but true winter does count for many things...crap =)...summer i got 300 to the tank, now i get like 270
i guess i need to do some research on this tonight.

I get about 200 to a tank...and my tank is probably bigger than yours!

digitaldrifter91 · Feb 10, 2004

hehe i have a 16.9 gallon capacity and fill up with 14.09

labman · Feb 10, 2004

I have long puzzled over this. I know enough thermodynamics to know that starting with a cold, denser charge, and exhausting it to a colder temperature should give better efficiency.

It is easy to understand why it is not enough to help on short trips, but I have always been disappointed on longer trips too, even when not bogged down by bad weather and traffic.

As for the thermodynamics of it, the colder intake may reduce the peak temperature. Then the exhaust temperature may be at the end of the expansion, not the tailpipe.

I suspect the winter fuel formulations, air resistance, and fluid viscositys may add up to more than any improved thermodynamics. On a warm day, the engine itself, with a good cooling system may be about the same temperature as in the cold, but we all know the beating the heat gives everything else from the tires to the transmission. Anybody have any rolling resistance figures for hot and cold?

TC · Feb 11, 2004

To expand on other's comments just one iddy bit, since colder air is denser, by definition it contains more oxygen (which is what we're after, of course) per volume of atmosphere. Turbochargers, superchargers, and nitrous oxide artificially achieve the same result, although on a much greater scale. I've always been under the impression that race cars such as dragsters and Nascar rides, assuming track surface conditions are the same, do best on cooler days.

The colder the ambient temperature, the longer it will take to reach normal engine operating temperature, and the longer the engine will be running rich while "choked" (carburetor) or it's electronically-driven equivalent (fuel injection), thereby increasing fuel consumption while warming up. But once warmed up, I would think that you have an optimum condition: the colder the air while driving, the more oxygen, the more energy avaiable during combustion, the better.

rpn453 · Feb 11, 2004

As long as your MAF sensor and O2 sensor are working properly it shouldn't make a difference, since it meters fuel based on mass of air flow in and excess oxygen. Unless the engine takes significantly longer to warm up, which I don't think will happen to any noticeable degree.
What may make a difference is the intake configuration, just as with an exhaust system modification. You may have made it better or worse, or modified the torque curve. Smoother flow through the intake and exhaust is always better for mileage and power, but increasing or decreasing the diameter will shift your torque peak up or down. This may also affect your mileage by reducing or increasing the engine's efficiency at a certain rpm. I don't think your mod would have a big difference on anything other than a couple more horsepower from the cooler air. A couple more horsepower is good though!

[ February 11, 2004, 10:21 PM: Message edited by: rpn453 ]

S2000driver · Feb 11, 2004

quote:

Originally posted by Shannow:
S2000, I disagree that the greater difference between inlet and exhaust temperatures means better efficiency.

Hottest exhaust temperatures will be obtained from a blowtorch, with zero thermal efficiency, as no work is extracted.

I made a mistake, it should be the difference between the maximum temperature in the combustion chamber vs. the intake temperature.

[ February 11, 2004, 01:50 PM: Message edited by: S2000driver ]

T-Keith · Feb 12, 2004

A CAI intake usually increases mileage, unless you notice a power increase causing you to drive more aggresively.

The reason cold weather decreases mileage is because it's much colder than 70deg "cold" air, and it takes longer for the vehicle to warm up.

-T

XS650 · Feb 12, 2004

quote:

Originally posted by T-Keith:
A CAI intake usually increases mileage, unless you notice a power increase causing you to drive more aggresively.

The reason cold weather decreases mileage is because it's much colder than 70deg "cold" air, and it takes longer for the vehicle to warm up.

-T

I think those are the effects most people notice. However, tires run cooler so are stiffer, wheel bearings differentials and tranmissions run cooler as does engine oil to some extent.

Aerodynamic drag is directly proportional to air density. Air at -30F is about 1.23 times as dense as air at 70F. Since aerodynamic drag is the biggest power absorber at highway speeds and the other stuff is a bit stiffer, a 23% increase in fuel consumption at highway speeds with a fully warmed up car at -30F is easily explained.

cold air=less mpg?

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