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Old 05-28-2011, 06:32 PM   #1
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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.




******************************
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?
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Old 05-28-2011, 07:15 PM   #2
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Re: All about hot air...

Quote:
Originally Posted by chriswf View Post
- 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?
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)...http://www.gassavers.org/showthread.php?t=244
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Old 05-28-2011, 07:21 PM   #3
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Re: All about hot air...

check out the gas log on this saturn...http://www.gassavers.org/garage/view/310
and this...http://s75.photobucket.com/albums/i3...emysan/saturn/
is yours a 5 speed?
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Old 05-29-2011, 05:04 AM   #4
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Re: All about hot air...

Quote:
Originally Posted by chriswf View Post
Okay so, I've read here in numerous spots that hot air usually equals to better gas mileage.
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.

Quote:
With this knowledge, and an understanding behind it that the ECU reads less air and gives less gas...
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.

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

Quote:
So, if hot air DOES increase MPG, that is probably why turbos increase mpg.
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.

Quote:
- Would dirty or clogged, or maybe even just a really restrictive air filter lead to higher gas mileage?
On a modern car it will have zero effect on fuel economy.

On a carbureted car it will cause lower fuel economy.

Quote:
- Does cold air ever give better mpgs than hot?
No.
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Old 06-03-2011, 10:15 AM   #5
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Re: All about hot air...

Quote:
Originally Posted by bowtieguy View Post
check out the gas log on this saturn...http://www.gassavers.org/garage/view/310
and this...http://s75.photobucket.com/albums/i3...emysan/saturn/
is yours a 5 speed?
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


Quote:
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.
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.
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Old 06-03-2011, 11:23 AM   #6
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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.
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Old 06-03-2011, 02:09 PM   #7
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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?
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Old 06-03-2011, 05:21 PM   #8
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Re: All about hot air...

Quote:
Originally Posted by BEEF View Post
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.
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.
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Old 06-03-2011, 05:24 PM   #9
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Re: All about hot air...

Oh yeah, 2 more things.
Does forum subscription work?
And can I not edit a post? (my own posts)
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Old 06-03-2011, 05:48 PM   #10
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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.
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