Has anyone heard of this? It's supposedly a trick for newer cars with O2 sensors and computers to get better gas mileage. You run a duct from somewhere with hot air, like the exhaust manifold, into the filter box to increase the temperature of the air into the engine. Supposedly the computer compensates by leaning the a/f mixture and increasing mileage (but decreasing power). Some folks on the Saturn board claim to be getting into the high 40s highway.

Seems to make sense, in theory anyway, although I'd have a hard time believing they are getting almost 20 mpg more over stock by this.

Couple thoughts on this...

1. If it leans it out, decrease horsepower, then wouldnt you have to put your foot into it more to get it going? So you'd kind of defeat the purpose right there...

2. If it was true again, then wouldn't people who live in Arizona and other really hot places get better gas mileage?

3. If it was true, then wouldn't auto manufacturs be doing something as simple as this to bump up the MPG???

I could be way off....but just my first thoughts that pop in my head...

It takes a certain amount of energy to make the car go or keep it going. Using hot air will produce less power so you will indeed have to press the throttle further open.

True the computer will reduce fuel with increased air temps. But again opening up the throttle a bit more will reduce this benefit to next to nothing or nothing.

What *could* happen is that the fuel atomizes and thus mixes and combusts better. This would be more efficient. But it would also be something the OEM would have discovered and tried too.

No way you would see a 20 MPG increase from this, maybe 2 MPG.

See this thead, he had an increase of 2 mpg.
http://www.saturnfans.com/forums/showthread.php?t=71674

and

http://www.saturnfans.com/forums/showthread.php?t=119056&highlight=hot+air+intake

See this thead, he had an increase of 2 mpg.
http://www.saturnfans.com/forums/showthread.php?t=71674

and

http://www.saturnfans.com/forums/showthread.php?t=119056&highlight=hot+air+intake


looks like the second person got almost 10%

I'll bet if effects driveability, which is why the car makers haven't done it. Making a car is a series of compromises.

I'll bet if you did this to a car, you'd have to change your driving habits as well.

Back to my cold air FI idea using the AC....so route lines for hot air / cold air to the intake. Run the heater when you want mileage and run the AC when you want raw power in your saturn. You have tuning on the fly with your AC / Heater controls.

Hook up a power inverter and hook up an electric blower to your cig lighter, route some tubing to your intake and whammo - you have a GREEN blower, you have reduced your carbon footprint and gained power.

We can market this and call it the Al Gore performance package. We will sell them at home depot.

Automakers go to great lengths to calibrate computers, ignition, and injectors for maximum efficiency. Sounds like a crock to me.

Automakers go to great lengths to calibrate computers, ignition, and injectors for maximum efficiency. Sounds like a crock to me.

I agree...

Automakers go to great lengths to calibrate computers, ignition, and injectors for maximum efficiency. Sounds like a crock to me.No, they don't... they go to great lengths to pass emissions testing, which requires running them rich.

You can easily re-program a car to increase its fuel efficiency, at the cost of not meeting emissions standards.

No, they don't... they go to great lengths to pass emissions testing, which requires running them rich.

You can easily re-program a car to increase its fuel efficiency, at the cost of not meeting emissions standards.

Not rich per se, but stoichiometric... engines can run a lot leaner than that but at the expense of NOx emissions. Emissions standards are met first, then fuel economy. Many cars that are sold in the US get several MPG less than their foreign counterparts simply because of more lax emissions standards outside the US, the foreign market cars are tuned for a leaner cruise mixture.

As far as the warm air thing, warm air is less dense, requiring more of it to generate the same HP as a cooler air charge. To generate the HP required to maintain cruise speed with warmer air requires more of it, and to get more air in requires the throttle blade be open more than with the cooler air charge. The more open throttle blade results in less manifold vacuum and thus reduced pumping losses. That right there will help fuel economy just a little bit... but not all that much. Much better results can be had by re-tuning for a very lean cruise, but at the expense of increased tailpipe emissions.

No, they don't... they go to great lengths to pass emissions testing, which requires running them rich.

You can easily re-program a car to increase its fuel efficiency, at the cost of not meeting emissions standards.

Maximum fuel economy and minimum emissions are both achieved by burning all the fuel.

Maximum fuel economy and minimum emissions are both achieved by burning all the fuel.

True, but minimum tailpipe emissions and maximum catalyst efficiency is achieved at/near stoichiometric (14.7:1 a/f) mixtures, while maximum light load fuel economy is achieved by running mixtures much leaner than 14.7:1, such as 15.5-16:1 or even leaner if the engine will tolerate it.

The problem is when you burn mixtures leaner than 14.7:1 the NOx emissions increase substantially, so to keep them within federal standards the costs increase-- now that you're outside the 14.7:1 range you need a wideband O2 sensor to provide accurate mixture readings to the ECM to maintain closed loop fuel control & trim and you also need a larger catalyst pack to reduce and break down the increased NOx levels to maintain tailpipe emissions under the standards. There is a bottom line to meet on all the cars, so they tune for the best economy they can achieve without spending tons of $$$ on a WB02 and larger catalysts. The classic example is the Honda Civic HX... it had a lean-cruise burn variant of the engine that was used in the rest of the lineup that got 5+ mpg better, but to keep tailpipe emissions in check it used a substantially more expensive and larger catalyst pack and also used a NTK wideband O2 sensor that's 5X the cost of the standard narrowband sensor.

The manufacturers meet emissions standards first as they have to meet emissions standards in order to be able to sell a vehicle, and then they tune for maximum fuel economy while still maintaining the tailpipe emissions while keeping the overall cost of the emissions control system in check.

Interesting, but I'm still not sure I follow where blowing hot air into the intake does anything positive. I would think the cooler air (higher density) would benefit efficiency if anything would. Engines don't get better MPG at high altitude.

Interesting, but I'm still not sure I follow where blowing hot air into the intake does anything positive. I would think the cooler air (higher density) would benefit efficiency if anything would. Engines don't get better MPG at high altitude.


Isnt it as simple as the PCM leaning out the mixture in hot weather to avoid detonation?

I tend to underthink these things but.....then again, odd that when I installed my Volant CAI that I GAINED mileage. Isnt that a spiel of all the CAI makers? Maybe thats a reference to flow rather than IAT.

Lord the FI stuff is over my head. Seems the more I read and try to learn the more confused I am by it....much like women. :D

I didn't read all of that first Saturn link, but the guy does a 40 mile round trip test @ 60mph and claims an increase in MPG? How about driving several tanks worth of gas to get more real world test results? Those Saturn guys are quirky though. I hear a lot put on bigger front tires to reduce the RPM's at highway speeds to get more MPG. If you're going to do a test, lay down some mileage!

Anybody read the article in USA Today a few weeks ago about some Honda Hybrid guys in Phoenix getting 100+ MPG? Coasting with engine off, drafting big rigs, driving as slow as possible, shutting off engine at lights; it was some funny reading. Most were recording MPG figures from the computer display (which I've noticed on my Sierra is incorrect). Heck my Chevelle could get over 20mpg driving places at 35mph!

Can't knock a guy for trying, but you drive 40 miles and you're getting 46+ mpg?? You didn't even drive 46 miles :clonk:

Can't knock a guy for trying, but you drive 40 miles and you're getting 46+ mpg?? You didn't even drive 46 miles :clonk:


lmao :D