All about hot air...
 

Okay so, I've read here in numerous spots that hot air usually equals to better gas mileage.

With this knowledge, and an understanding behind it that the ECU reads less air and gives less gas... I've opened my mouth around SEVERAL people only to have them try to shut me out as soon as possible.

It's under their impression that cold air intakes, and cold air delivery and such, will give you better MPGz.

I have a Saturn SL2, plastic pointy car, and I'm doing about 43-46 on a loop here in Texas. Yes, my gas mileage increased when the heat increased. I got a 20 and a 40 mile loop I can do mid day (hot time of day, low traffic so I can 55mph it)... I can do 46mpg on both my loops. That's with no antenna (since I listen to cds) and wind shield wipers. It was 100 degrees here in Texas when I tested this. No drafting or coasting, but cars did lead me by a couple of car lengths ahead of me.

So, if hot air DOES increase MPG, that is probably why turbos increase mpg. People say it's like atomized air, and chops it up and stuff... But it would make more sense that the heat from the turbo is better gas mileage.




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So this leads me to my questions:

- Are turbos real mpg increase due to the exhaust heat they radiate?
- Would dirty or clogged, or maybe even just a really restrictive air filter lead to higher gas mileage?
- Does cold air ever give better mpgs than hot?

Re: All about hot air...
 

turbo chargers do not increase mpg--an identical engine non turbo yields more

restricted air filter would not increase mpg--tho restricted does not guarantee a loss either

cold air intakes are said to yield more mpg under wide open throttle applications
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saturns are believed to benefit(mpg) form WAI(warm air intake)...https://www.gassavers.org/showthread.php?t=244

Re: All about hot air...
 

check out the gas log on this saturn...https://www.gassavers.org/garage/view/310
and this...https://s75.photobucket.com/albums/i3...emysan/saturn/
is yours a 5 speed?

Re: All about hot air...
 

To be more accurate: Some cars get better fuel economy with hot intake air. For many (perhaps most) there is no effect.

Other than that, if we're talking hot vs. cold weather, there's more to it than intake air temperature. Here's just a few of the variables involved...
- Air density's effect on aerodynamic drag
- Winter vs. summer blend fuel
- Warm-up time
- Extra idling
- Fan vs. no fan vs. windows open vs. A/C
There's more but I can never remember them all.

The ECU reads or calculates mass of air, not volume. It then adjusts based on the combustion results as read by the O2 sensor. If it's not programmed to run lean then it won't run lean.

It is a common misconception. It is mainly the result of marketing, although there is a technical history behind it (which hasn't been valid for decades). Old cars used to have restrictive intakes that could cause additional pumping losses for drivers who are more interested in going fast than saving fuel. Older cars than that got their air under the hood, where sometimes it was too hot.

That's quite a jump in logic. They do so much more than heat the air; they create exhaust backpressure, require you to retard your timing, and generally call for a lower compression ratio, among other things that reduce fuel economy.

The reason turbos have a reputation for increasing MPG is because they are used when replacing a big-displacement engine with a more efficient small-displacement engine. The turbo's job in that context is to let the driver have the same power available but drive around with a more efficient smaller engine when not using that power.

If you take an existing car and slap a turbo on it, your fuel economy will decrease.

On a modern car it will have zero effect on fuel economy.

On a carbureted car it will cause lower fuel economy.

No.

Re: All about hot air...
 

Yeah it's a 5 speed. I think 55mpg like that Saturn would be pretty hard w/o having his mods. And he even did 70mpg once.... I drove it very softly when I got my high mpgs. And, Yeah I saw his layout about 2 months ago I think - very neat :P


Okay so, if I had my car grabbing air from outside or under the car where it was cooler, and removed the vacuum which takes the hot air out of my engine head... I wouldn't see a decline in fuel economy?

I swear I've read on here somewhere, that guys were specifically placing their air pickup filter locations somewhere - where it would be warmer. And it was supposed to make a huge difference.
Like the car would see the hot air as making a rich mixture, so it'd decrease the fuel it gives the cylinders. Causing it to run at a lower amount of fuel over all. Or maybe just at idle. I don't know. I can't find the posts anywhere.

Re: All about hot air...
 

there have been several experiments by numerous people on this one.

it seems to work on saturns and similar vehicles (cavaliers, sunfires, etc.) I think it has a lot more to do with their programming and less to do with the other technical stuff. yes, you are taking in less oxygen per charge but the computer compensates for that in other vehicles (with different programming).

it has also been suggested that it changes your throttle response and that is the difference people see. instead of your range being from 0-100 (where 0 is no pedal and 100 being WOT) your range is 0-60 where as you have to give it more pedal to achieve the same results as far as power. obviously WOT is still there as it enriches the mix and runs a pre-programmed map within the ECU but you see what I am saying.

the people that get insanely good MPG usually are the ones using EOC or engine off coasting. there is a guy with a cavalier like mine (though a 5 speed) that is achieving close to 70MPG. he told me in a PM that his car is only running about 60% of his commute.

if it does help, this is a topic that is often discussed and often argued (both for and against). I used to be a hardcore believer in this but at the same time when others see differing results, you can only say that it either works or doesn't work for you in your situation. the consistency seems to be more with the saturns and similar and not an across the board increase for anyone that tries it.

Re: All about hot air...
 

Most of the increase in mpg from a warm air intake is due to reduced throttling losses. Cars with gas engines operate with th throttle partly closed most of the time.

An engine is an air pump, and pulling air across a restriction like a throttle plate or a dirty air filter takes energy. When you add EGR or WAI at part throttle, the throttle must open wider for a given amount of oxygen. This reduces manifold vacuum and the amount of work the engine has to do to pull in a given amount of oxygen for the gas.

However, at FULL THROTTLE WAI and EGR hurt efficiency. But which gassavers ever use full throttle?

Re: All about hot air...
 

OHHHHH that's what EOC means. Now I get it. Do they actually manually turn it off? Or is it clutch fully in - activated? (I know some people who have clutch in - car shut off on shift for racing, somehow keeps turbo spooling).
Then what, to turn it back on to accelerate again they just put it in gear and let the car start itself sort of like a really fast push start?
Never thought of doing this. There's plenty of roads where I've coasted in neutral for like a 1/4 mile and hardly dropped 5mph. It's sort of how Plano is designed and paved :P Slight hills here and there.

WITHOUT clutch starting it I could only imagine it'd woop your starter hard.
Man, I really wanna try this EoC thing now.

Re: All about hot air...
 

Oh yeah, 2 more things.
Does forum subscription work?
And can I not edit a post? (my own posts)

Re: All about hot air...
 

ok, first off, I guess you never push started your car. being a poor kid with poor friends, we tended to always have a friend with a dead battery or bad starter. you simply put it in gear and let out the clutch and off you go (after all your friends give you a good shove). same concept.

subscriptions should work though you have to check a box or something. I usually don't subscribe as it tends to fill my email account and it is a work email. but should be pretty straight forward.

I think you have a limited time to edit posts and you may not be able to edit posts yet as you are a newcomer (notice the title of greenhorn under your username) we've been having issues with spammers so a lot of that has changed lately but I will admit the spamming is down.

I don't do the EOCing but from what I hear, you get up to speed, pop it in neutral and kill the ignition, put the key position back in the run position (just shy of hitting the starter) and once your speed has dropped a certain amount you put it in gear and slowly let off the clutch...and repeat. there is also pulse and glide which is similar but you don't kill the engine. you get going say 5 or so over the speed limit and let off the gas (glide) until you are say 5 mph under the speed limit. then you get on the gas (pulse) to get back to the 5 over again. several people have said that this is pretty effective.

regardless I would say to get a scangauge or ultragauge so that you know what your car is doing. mine actually tells me how warm my intake air is so I know how hot my hot air intake is running. it also tells MPG and a lot of other stuff.

start a garage and start keeping track of all your fills. that will help you find out what is working and what isn't.

***edit***

forget the first part, didn't catch your entire post at first. sorry, long day and winding down hard. coherency is low right now.

Re: All about hot air...
 

How to EOC:

1. Declutch or shift to neutral and turn key to "Off".
2. As soon as engine has stopped turning, turn key back to "On" but don't start it.
3. When you're ready to restart, put it in 5th gear (or a lower gear if you're going really slow, but I think most cars will start in 5th above 20mph) and bring the clutch pedal part-way up, like you're trying to hold the car on a hill. Don't wait for the engine to fire up, just let it kick the engine over for a moment, then step the clutch pedal back down to the floor. The engine will start.

On forum subscriptions:
You can subscribe with or without email notifications. It should work fine. You can change your user options to automatically subscribe to threads where you post (although that won't work when you use the Quick Reply box).

This forum has just the right amount of traffic that I've just bookmarked "View Recent Posts" and I check it a few times a day...no need for me to pick certain threads to keep up with, I visit them all.

Re: All about hot air...
 

About hot air, more specifically intake manifolds. They are definitley hot. Hondata did an intake manifold gasket that isolated heat transfer to the manifold and gained some power, so it is obvious that a colder manifold makes more power. A hot manifold should heat up the air for more efficienty. OK, so far it's hot and cold, but what impresses me most is the way this thing works. At low load/low rpm where you want mpg, the air moves slow and it has time to heat up, so you have mpg, at high load/ high rpm where you want power, air moves fast and it dosen't have time to heat up, so you have power. It's BRILIANT (i think). The intake manifold temperature could be a tuning tool betwen mpg/power without compromising to much. I have seen old cars with 2valve/piston with intake manifold casted togeder with the exhaust manifold, so this could be taken very far. But before that i would like to hear your opinion on this.

Re: All about hot air...
 

On my twin tubo car I want denser cool air to make max power. The hotter the air the less dense it is, the less power. For this car it is all about power, not mpg. It gets about 13 mpg ( my foot is in it all the time). For me fall and winter and early spring means more power, summer not so much.

Re: All about hot air...
 

Speaking on intake manifolds getting exhaust heat, the Early Fuel Evaporation system on my 1980 Buick pumps exhaust through channels in the intake manifold when the engine is cold to make it warm up more quickly, partly for driveability and partly for fuel economy.

Re: All about hot air...
 

I stopped caring about the science behind it and/or proving/disproving the theory that hot air works to increase MPG. You're driving a Saturn S-series... IT WORKS... VERY WELL.

Go to my garage and read up on my SL2 which is now retired if you want more info.

/thread

Re: All about hot air...
 

The science is important for these reasons:
1. To help convince people to try it
2. To develop related strategies and technologies that might apply to other vehicles that don't work with it

However, results are certainly a good thing on their own!

Re: All about hot air...
 

we all know what hot/warm air does to the engine. there are factors that are being overlooked when it comes to saving fuel. i know some but im pretty sure you guys have more.

transmission: preferably low gear ratio. having lower rpm during cruising makes it harder for the engine to maintain rpm, in return engine load increases and so we call that throttling. if a high gear ratio lets you cruise 4000rpm @60mph, peak torque is near the powerband and maintaining or even accelerating is easier, meaning high vaccum/pumping loss. also consider 4000rm on a 4 cylinder is like a v8 cruising @2000rpm if we were to relate them. the power/cfm/afr might be the same given the instance. and friction is also higher...

displacement: overly large displacement will not yeild any improvement on wai/hai. engine is too powerful to maintain high loads during cruising. very small displacement will almost gain nothing since load is kept constanly high during cruising. i would choose a displacement of 2 to 3 litre if i were to practice wai/hai.

one example i remember is mr. serntraSE-R's scion xb. massive drag coefficient, 1.5ton weight and 1.5 litre engine. he did a lot of tests and unfortunately didnt gain anything.

tuning: megasquirt is not very expensive or used aem ems wiring is not very complicated if you were to convert them.. lean the engine out up until bucking and missfires, then increase the timing. ive tuned some cars that gained 20-40% fuel economy. in my car with a 4.4 final drive and awd i cant gain any as much as i did with my old transmission (which was 4.0) no matter how much i tune the engine. so meaning you can only do so much given the factors that ive noticed.

Re: All about hot air...
 

The cold / hot air answer boils down to two facts:

1. At Wide Open Throttle, an engine drawing in cold air will produce more power and will use less gas per horsepower. The "Brake Specific Fuel Consumption" is less.

2. Automobile engines hardly ever operate at WOT. They are throttled under most conditions. Warm (less dense) air reduces the work an engine has to expend to draw air across the throttle. This improves real world mileage. EGR has a similar effect.

Re: All about hot air...
 

I agree that at WOT cold air with produce more power, but why would it use less fuel per horsepower?

Re: All about hot air...
 

I think since Saturn S-series see widespread success and they are one of very few vehicles people try to hypermile in that only uses a MAP sensor, it really comes down to does your car have MAP or MAF? MAP = success w/ HAI, MAF = won't make a difference because the engine is going to retune and adjust to the increased intake air temps.

Scion xB = MAF
Saturn S-Series = MAP


MAF is much more complicated and MAP is kinda bare essential.

This is usually easy to see which one you have. If there's a sensor with either honeycomb looking stuff or a wire running through it in your intake tubing before entering your throttle body, you've got a MAF car and you shouldn't waste your time with a HAI. That wire reads the mass of the air in relation to temperature of the air and adjusts accordingly to keep your engine runnings at factory set levels..... you cannot trick this sensor or avoid using it without extensive work.

Re: All about hot air...
 

Because horsepower and fuel consumption aren't ALWAYS linear. Sometimes while dyno tuning people find that removing fuel actually increases horsepower substantially.

More AIR = more power... hence turbocharging. Yes this generally requires more fuel too, but not enough to cancel out.

Re: All about hot air...
 

less fuel per hp on cold temp? beats the purpose of wai/hai plus temp only determines the density of air.

map and maf.. a lot of misconception here guys.

both uses correction factor, theres air temp sensor, barometric sensor, oxygen,tps... almost all engine management systems can use both sensor, its just a matter of voltage offset to run them properly.merely preferrence if you were going to choose either one with manufacturers, GM didnt use ait at some point because they were using resistive wire for their maf, with that they can calculate temp along with tps but not accurately. now almost everyone incorporated maf with ait in the same sensor. thats less parts to buy and less man hours to manufacture and install. with map sensor you cant have both in the same package because ait must not be inside the intake manifold, we all know as the pressure drops when tb is closed the temp also drops.

Re: All about hot air...
 

I installed a K & N Typhoon intake on my 2008 Civic Si. It still has a tube connecting it to the cold air supply, but it is no longer sealed in a box. Therefore, the intake has access to the hot air under the (packed) engine bay. Prior to installation, my intake air usually did not crack 90 degrees. Now it averages 110, and I have seen it jump to 145 while sitting at a red light in 90+ degree weather without the engine running (hence, no fan).

Prior to installation of the intake, I had 2 tanks at 32-33 mpg. After the installation, I am averaging 36 mpg, and as high as 38 in mixed driving. Not bad for a car that is rated as 29 mpg highway and 25 mpg combined. I do not P&G much; I'd get run over. I drive 55 - 65 mph on my commute, and draft when I can. I attribute the gain in mpg almost solely to the warmer intake air.

Re: All about hot air...
 

At least one reason is that engine friction is not directly proportional to power output. For example, friction (drag) due to oil viscosity is independent of power. There are other factors too, such as water and oil pumping that are somewhat independent.