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Discussion Starter #1
The known thing with intake is that cool air (being denser than hot air) coming into the engine is better for performance.
But is one opposite true for hot air: is hot air (less dense) better for mpg's?

My theoretical ramblings on the topic:
So hot air is less dense, so if the air coming into the engine at a set rpm is less total air, that also means less gas is being put into the air at a given gas pedal and engine speed.
Thus presto! better mpg. (at least in a world where the acceleration can be really slow, and the vast majority of driving is on level ground in top gear with the mpg limited more by gearing than any other consideration.)

On the other hand, if the driver has a heavy foot the equation of hot air is better for mpg gets tossed and who knows what the result would be..
(I tried Google.. and just no answers I can find...)

Other positives of air intake inside engine bay: cools engine bay, sucks heat from engine bay and sends it out exhaust. (and less into passenger compartment.. The Focus seems to allow a lot of engine heat into the passenger compartment..)
Allows kysor shutters to stay closed more, with radiator more efficient with cooler area behind radiator..
So.. anyone with any experience? or comments?

One reason for this idea was I wondered if it being hot outside, helped my mpgs..
vs being colder.

I may try taking the air cleaner top off and seeing what happens with my late-night freeway loop testing grounds.. LOL
 

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Hot air intake is supposed to give you less power but better mpg.
Reverse Turbo.
 

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No. The same amount of oxygen mixed with the same amount of air will always produce the same amount of energy during combustion. The ECU accounts for this by measuring the temperature of the incoming air. It may include less fuel at a given speed due to the hot air but the power produced from each stroke will be proportionality less due to this. This leads to needing a higher engine speed to produce the same amount of power to overcome the cumulative sources of resistance.

This effect may be small, but empirically it is a molar math certainty.
 

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No... It may include less fuel at a given speed due to the hot air but the power produced from each stroke will be proportionality less due to this. This leads to needing a higher engine speed to produce the same amount of power to overcome the cumulative sources of resistance.
I think this might be more true with an automatic transmission - but isn't a manual transmission basically geared directly to the engine? I thought the engine ran at the same RPM (given the same gear) at a specific speed. I'm not 100% sure how this works, but I think Elizabeth might be on to something...

EDIT: I also remember reading something about flame speed or something that helps with gas mileage.
 

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Hatch Nation #136
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A reduction in power will result in an increase in the amount of work needed to accomplish the same goal, ie a certain speed at a certain gearing. If it is not able to produce the power at a lower RPM to hold the speed needed, you must increase RPM to maintain that speed. The more revolutions of the motor the more your injectors must fire, filling your engine displacement with fuel.



So, if you are attempting to hold 45 MPH and it only requires 2k RPM and then you reduce your power so that holding 45 MPH requires 2.5k RPM each injector will fire an additional 62.5 times a minute, or about once a second. The mild gain you experience in having a leaner mix will be more offset by the frequency of filling your engine displacement.
 

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In my opinion just by doing some internal deductive reasoning, I figure that hot air would in turn make your engine hotter, therefore causing the radiator shutters to open more frequently to try to cool the engine, effectively hurting the aerodynamics of your car. Which would cause your gas mileage to increase due to increased drag.
 

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Hot air kills HP in a big way -- and also causes you to turn on the A/C sapping a few more HP. But your question wasn't about max HP, it was about fuel economy.

On the plus side, cars will almost always get better gas mileage in the summer months because the car spends much less time running when cold where fuel enrichment is present. The warmup cycle will be much reduced in the summer. That is probably the biggest factor.

Engines are designed to run most efficiently when warm and that's why doing things like changing to a cooler thermostat impact both fuel economy, emissions, and longevity of your engine.

Smaller factors impacting fuel economy when it is warm out would include decreased rolling resistance from tires and less aerodynamic drag from pushing the car through thinner, less dense, air (more of a factor at higher speeds).
 

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If pre-heating the intake air was all that is required to improve mileage during normal driving then car makers would be doing that already.

Cars have used that method for decades for the warm-up phase of driving, but it cut out for normal operation. They could just have a solenoid controlled flap to switch to cool air for acceleration. But since they don't do that you can be sure it doesn't work, or the benefit is too trivial for the extra cost.
 

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If pre-heating the intake air was all that is required to improve mileage during normal driving then car makers would be doing that already.

Cars have used that method for decades for the warm-up phase of driving, but it cut out for normal operation. They could just have a solenoid controlled flap to switch to cool air for acceleration. But since they don't do that you can be sure it doesn't work, or the benefit is too trivial for the extra cost.
I agree - I bet the engineers at Ford know better than I do. In addition, vast changes in air temperature (e.g. if you accelerate and a solenoid changes the air from 110F (WAI) to 30F (winter ambient) might end up warping the engine block or something ridiculous. Again - I'm no expert, but I do have a good background on the subject matter.
 

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Discussion Starter #11
Thanks for the thoughtful responses!
I can see where folks are correct about many of the things mentioned.
So i will just skip my pipedream...[cheers]
 

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Theoretically you are correct, warmer air will net you better fuel economy but less power.

Most modern ECU's have an IAT enrichment table which modifies the injector pulse width depending on the temperature of the incoming air. If you're looking for more fuel economy I would look elsewhere. High IAT kill you on two fronts. 1) High IAT's affect cylinder temperatures, and because you want to avoid excessively high cylinder temps the ECU is programed to pull timing to help control the temps. 2) The aforementioned IAT enrichment tables will limit the amount of fuel being injected. Those two reason can greatly effect power, and in extreme cases can even cause engine failure, but that not really something you need to worry about on an N/A engine.
 

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Keep on searching,
The keyword is WAI (Warm air intake)
There is a lot of information on the net on the subject.
It is a contraversial subject.
Then make up your own mind.
 

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Discussion Starter #14
Keep on searching,
The keyword is WAI (Warm air intake)
There is a lot of information on the net on the subject.
It is a contraversial subject.
Then make up your own mind.
Thanks!
IT is always good to know the 'right' words to search with.
I will do some further research.
Thanks again!
 

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I have been drag racing for years now and heat is our enemy. Heat equals friction/power loss. when ever I am at the track I never see people heating they engines for the next race. you even see people dumping buckets of ice over the engine block, super chargers and air intake tubes. a couple other things to take into mind when trying to test for gas mileage, 1.) drive your 20 mile loop then replace the gas burnt, maybe .5 gallons then do it again. 2.) barometric pressure changes, do all your testing in 1 day and try to do it while the barometric pressure is not changing and the outside temperature is the same. Drag racing a a 6000 foot elevation is not as fun as sea level so the racing in Colorado have to deal with the smallest changes, sometimes in Colorado the corrected barometric pressure goes above 7500 feet that equals slow day at the track. Other days you might see a pressure system come in and the correct pressure is 5000 feet= faster day at the track. things we all don't like as well
drag co-effeicent
head winds
side winds
rolling resistance
In a perfect world we would all drive in a vacuum.

I still want to place a large directional electronic magnet up in the front bumper so that I can activate it when I get close to the car in front of me, then I can have him pull me.
 

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Discussion Starter #16
I still want to place a large directional electronic magnet up in the front bumper so that I can activate it when I get close to the car in front of me, then I can have him pull me.
I always wanted a clamp 'grabber' on an extendable pole.. Then one could sneak up on a semi and grab on that rear bar across the back..
It would be a little too visible though.. other semi drivers would call the one being 'vampirised'.
Or some sort of device to snick/shoot out a thin cable, clear but strong monfilament,, to lock on the back end on the truck, then string it out so you get towed at say two car lengths, and can snip the cable off instantly...
[nono]
 

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In a perfect world we would all drive in a vacuum.

I still want to place a large directional electronic magnet up in the front bumper so that I can activate it when I get close to the car in front of me, then I can have him pull me.
Good idea. It'd probably work better on 18 wheelers than on something like a Saturn.
 

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Works on Zetecs fairly well fyi
 

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A reduction in power will result in an increase in the amount of work needed to accomplish the same goal, ie a certain speed at a certain gearing. If it is not able to produce the power at a lower RPM to hold the speed needed, you must increase RPM to maintain that speed. The more revolutions of the motor the more your injectors must fire, filling your engine displacement with fuel.



So, if you are attempting to hold 45 MPH and it only requires 2k RPM and then you reduce your power so that holding 45 MPH requires 2.5k RPM each injector will fire an additional 62.5 times a minute, or about once a second. The mild gain you experience in having a leaner mix will be more offset by the frequency of filling your engine displacement.


This logic only works on CVTs.

Engine Speed in any gear will result in the exact same traveling speed every time. The gears are fixed ratios. NOW if you have a lot of torque you can drive in a higher gear than you would otherwise, but that isn't what we are talking about. 2000 RPMs in 4th gear will ALWAYS result in the same MPH regardless of the amount of power you are generating.
 

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This logic only works on CVTs.

Engine Speed in any gear will result in the exact same traveling speed every time. The gears are fixed ratios. NOW if you have a lot of torque you can drive in a higher gear than you would otherwise, but that isn't what we are talking about. 2000 RPMs in 4th gear will ALWAYS result in the same MPH regardless of the amount of power you are generating.
That's what I was saying! There isn't any slipping once we're in gear, right? So if you're going a specific RPM - aren't you going a specific speed? There are torque losses but not rotational losses - unless something is slipping.

I'll go into test mode on the way home and check my speed/RPM in cruise control to see if hills change anything.
 
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