just curious since temps around here are starting to get really cold at this time of year and know that cold air can effect gas mileage and so forth
wonder if anyone has tried a hot air box setup for those winter months to help out with gas and car warm up

 

I don't think warmer air will help gas mileage at all since cars run more efficiently/better with colder air.

Also, your car warming up is not dependent on the temperature of the air going into your engine.

 

hot air is bad............. period.. cold air is good

 

cars will make more power with cold air as far as gas mileage and efficiency and such it goes up with hot air.
it allows one to open the throttle more reducing pumping loss through the intake tract, allows the fuel to atomise a little better, and think about it our motors generate heat and that heat builds pressure
how is cold going to make it more efficient?

all the cold air does is make it moer dense which allows more air per ci
but doesn't mean more efficient air per ci

 

lol. okay, where did you hear this?

and about the last comment, the air isn't more effecient more effecient per cubic inch when its cold, but if its more dense, then there is MORE of that same effecient air going into the engine.

 

Its not so much the fact that the air is cold, but the air is dense.

Generally speaking, cold air as we know in it in the atmousphere is more dense than warm air. However so is not the case when you compare elevations...

Since O2 is heavier than some other gasses presant in the amousphere, its pulled close to earth's core. Hence the lower the amousphere, the higher the denisty of O2 compared to other gasses in the "air".

The higher the O2 concentration (density), the more go go juice for fuel injected cars (carbs need rejetting, fuel inject have sensors to check the density of the intake).

BUT... the higher you go, the less dence the O2 is, BUT the colder the temperature. This actually is the entire theory behind wind (well that and earth's spin on its axis).

Warm air won't help the car run any better unless the warmer air is *more* dense than high elevation cold air. Most cars have better ETS on a drag in florida(5-10 feet elv.) next to the coast, then the will in a drag in Denver (5400 feet elv) even though the temperature in denver is probably less warm than in florida, respectfully.

BUT...

If you take a cold air (per elevation, think denver) and heat it in the engine bay of your car before its sent to the engine, you are ONLY warming the less dense air, by no means are you making it more dense. Infact you're making it less dense and causing some funky air turbulance/pressure in the process.

Idealy your car wants to breath unchanged (but filtered) air from outside the car. At nothign else, making a CO2 or air/air cooler is used to increase density. A air warmer would be counter productive.

 

engines will operate more efficiently with more throttle usage.
yes that seems counter productive to efficiency since gas mileage will go down but that is due to more air being drawn into the motor and more air means more fuel. still though the fact remains that per amount of fuel you use it is being used more efficiently.
BSFC brake specific fuel consumption.
when the throttle is open more you are reducing pumping losses placed on the engine itself due to the throttle.
when your throttle is closed more it creates a higher vaccume that the engine has to work against to pull the air in through.
hotter air being less dense means more throttle opening to pull in the same amount of air mass wise (sure your pulling in more volume but mass should be close to the same)

and engines do tend to run more efficient when warmer also ( not talking air just talking the motor itself)
think about what a motor does. it takes in air and fuel. compresses them then makes it go boom. that boom creates heat and hot gasses expand correct? that expanding creates pressure. that pressure moves the rotor/piston ( again whatever ) which drives you down the road. if your motor is running a little colder what it tends to do is cool the combustion proccess which limits the amount of pressure that the combustion proccess is able to give.
now I admit I gave a little assuming with the hot air being able to help out a little on the combusion procces but still I stand by my idea with the hot air going to help reduce pumping losses untill I can be shown otherwise.

"and about the last comment, the air isn't more effecient more effecient per cubic inch when its cold, but if its more dense, then there is MORE of that same effecient air going into the engine."
so by taking this last post of yours the way I see it is cold air hot air both just as efficient as one another. only thing is when the air is cold you have more air going into the motor. so whats that mean? more gas gets burned. so that means less gas mileage correct?

I'm not worried about power guys. I mean come on do I really want to have more power when I'm driving around on a nice big sheet of ice for an 1 1/2 hour drive?
so all this talk about et's drag racing on ice isn't my cup of tea.


I'm just trying to see if it has been done or if someone can actually correct me here rather then just say "lol your wrong" show me prove me wrong. I don't mean that as a I'm better then you statement but please if your going to say I'm wrong tell me why. (this is to the first two ppl who posted)

 

Umm, adding heat to a machine NEVER makes it more efficient. Ever. Not in a million bajillion years. It's a law of physics. Heat = bad.

So I don't see how increasing the engines temp by having warm air instead of cool air is going to increase gas mileage :P

 

Unless the warm air is more dense than the cold air. Like i said it is possible, just we're working towards making trinity in the process... But its a rotary... if there would be one engine that could work towards a nuclear blast just by heating its intake charge...

 

Carbed cars usually have a 'stove'

That is, a line of intake air that warms itself up by the exhaust manifold

This is for cold weather starting.

 

What's funny is that I was just discussing this on the weekend. I am making a hot air intake system for my Insight, to pull air of the precat.

Tests have shown (both by me and other owners) that having the hot air box makes warmup quicker, and allows the car to enter lean-burn when the temps are otherwise too cold. For the Insight, this means that you don't take as big a mileage hit in the winter. In the summer, I usually do abvout 70 MPG in the city, in the winter it drops to 50...I'm hoping that my hot air system will bring it back up to 65MPG or so.

However, in the RX-7, there's no point.

 

It's also to stop Carburator Icing... Not a problem with FI cars.

Even in Carb'd cars, the Stove will have a mechanical flap that either blocks the stove letting cold air in, or it blocks the cold air and takes air from the stove pipe. Once the car is warmed, that flap should close, and only take in cold air.

 

70MPG?! how big is the gas tank?! a 10 gallon tank would last forever and a day!

 

10.5 gallons.

70 is my city mileage. I often do over 90 MPG on the highway, and sometimes over 100 MPG on a nice day...

 

can you explain the density thing though without going into drag racing and et's and such
only talking gas mileage, and the car running a little better in these not so fun temps

 

you still didn't really explain things


heat = bad you say
care to GO INTO DETAIL?

I already tried going into detail
and heat in an internal combution motor does make for efficiency
again heat = pressure
if we remove all heat from the combustion proccess we get no pressure and there goes ALL efficiency if your not getting pressure on a internal combustion motor


once again before you chime in explain please. not just well it's wrong go explain why it's wrong

anyone can say it's wrong doesn't mean it's right and without saying why it's wrong doesn't lend you any credibility

 

Mr Cake!

Why would it be totaly ineffective on a 7? I could put a switch on my car to allow it (on those long highway cruises) to grab hot air off my radiator or something.

 

u rx7 is a preformance car lol yo generaly dont want it to produce LESS power but more. an insight tho is all about gas milage. if someone put a hot air intake on an rx7 they need to be smacked

 

I'm really confused, rxspeed87, it seems like you're saying the more you open the throttle, the less fuel you will use... care to explain this? you said something about like, the engine will have to pull less of a vacuum, which will.... make it easier for the engine to... pull in air? is that what your'e saying?

also, you're thing with Heat = pressure, so that means heat is good.... I'm sooooooo confused with what you are saying. because, the only place you want pressure is inside the combustion chamber, after the combustion occurs. and the more dense the air coming into the engine is, the better the combustion will be, which will cause heat, which will expand, and will make the rotor turn(or piston go down in a piston engine).

also, the fuel system in the RX7 injects fuel mainly based on air volume going into the engine, as well as throttle position. now, if we open the throttle more, like you were suggesting, then the volume of air going into the engine is greater, and the throttle position is greater, so more fuel will be injected. now, if we put cold air into the engine, the air will mix better with the fuel, and also, more of the air will be usable in the combustion process. this will allow us to leave the throttle more closed, which will pull in less air, and inject less fuel into the engine.

and once again, hot air will help with warm up, because when the engine is cold, the fuel sticks to the walls of the intake manifold, so not as much fuel makes it to the combustion chamber. to make up for this, the ECU injects more fuel into the engine. but once the engine is warm enough, the fuel will not stick any more, so this isn't neccesary.

 

and someone trying to make the most power they can when driving on a sheet of ice should be praised?


once again winter time.
ice, snow crap like hat
I don't want to make the most power I can

if driving as fast as you can and making as much power as you can to go show your performance on a piece of ice is your thing then go for it.

but for me during this time I would rather have a litle more efficiency

 

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the more the throttle is open the more efficient the motor will run. again pumping losses. if the density is the same though throught the throttle opening yes you will use more fuel at more throttle though it will be used more efficiently. try looking at bsfc numbers for partial throttle vs full throttle.
and cold air being more dense requires less throttle opening to bring in the same mass of air.
when air gets heated up the density goes down so it requires more throttle opening to get the same mass. this greater throttle opening will reduce pumping losses I would think.
if you think of it in just terms of throttle opening your not going to get it. need to also think of density of the air itself. the hot air being less dense will still hold the same amount of air just take up more space to do it so you open the throttle a little more it allows that extra volume (not density) of air into the cylinder.
so you really bringing in the asme amount of air so the same amount of fuel should be used.


density of the air changes once it hits the cylinder being it gets compressed.
so yeah the more compression you run (which will make the air dense) the better of you are and more efficient you run.
but tell me whats the difference between
1lb of air that takes up 10ft of space vs 1lb of air that atkes up 20ft of space?
they still both hold the same amount of air both would burn the same amount of fuel correct?
but putting it in place of an internal combustion motor the less dense one will help out a little for efficiency due to pumping loss issues.



even a vaf isn't limited to only volume but density as well
more dense air has more mass to it which would push the flapper door open more so then the less dense air. there are also more sensors then just the vaf and throttle sensor. the there are two temps sensors on the intake which help compensate for the higher volume of air that is brought in and a o2 sensor that will try to keepyour car near stoic as well

with the fuel injectors on our car they are for the most part right at the port so not too much fuel will stick the manifolds as is.

 

btw thank you for at least trying to explain this time

and if I do end up being wrong on this I willadmit it but still need more to let me know I'm wrong

 

okay. well, I understand what your saying now, It just doesn't sound right to me. its like saying you'll get better gas mileage on a 110 degree day in Denver(wouldn't that be something ) than a 60 degree day in Morrow bay, CA. which I have experienced(for the most part), and gas mileage is better down in CA, since the air is more dense.

well, whatever. we both seem to be standing strong behind what we're saying, so the only thing would be to get out there and try it. and if it does help, that would be awesome!

 

true I agree retard :p hey it is your name
just need to figure out something that would help create a hot air box.


but also there comes other isses with what you are talking abuot with denver vs cali regarding moisture. smog and all kinds of other things in the air that might be able to change how it would run

 

yeah, I know there are a lot of other factors, but I'm just trying to keep it simple.

umm, for the hot air box, why not build a little alluminum box around the exhaust manifold, and run a tube from the box to the intake area. then make a cold air box type thing around the filter, but put the hose from the exhaust manifold into the "cold air box" around the filter. then, there you go. it'd be just like the setup from some old carburated car.