EcoModding for Beginners: Getting great gas mileage.

[PA32R]

Originally Posted by SVOboy

This is an article from my website, www.crxmpg.com, ...
2 - Slow down!
Air resistance increases exponentially with speed, so slow down! The difference between 55 and 75 is astronomical...

Though it doesn't change your point, air resistance doesn't increase exponentially with speed: r=ce^(ks), it increases as a power of speed: r=ks^2. Here, r is resistance, c and k constants, s is speed.

Misuse of "exponentially" is a pet peeve of mine, sorry.

[toomuch]

Originally Posted by PA32R

Misuse of "exponentially" is a pet peeve of mine, sorry.

I agree!
But nice post SVOboy.
I just don't understand how warmer air can increase efficiency.
However I have not done any research myself.
Since Cold Air Intakes take in denser air, which stuffs more oxygen in the explosion chamber, I guess it the computer puts in more fuel to compensate. Maybe that is why.
There probably is a whole thread on this somewhere, so sorry for not searching. I'll check later.

[JohnnyGrey]

As noted, some of those intake and exhaust mods only work with old school, non computerized engines. Less restriction on intake or exhaust does not always equal better efficiency on modern computer controlled engines.

These mods have the effect of leaning out the mixture on open loop cars because they let more air in. Modern ECUs will match that extra air with extra fuel.

[jcantara]

Originally Posted by Winston

It is interesting reading about the contrasting theories of "increased Hp/efficiency results in better mpg" ie less restrictive intake or exhaust, or the "reduced hp = greater throttle opening req'd which reduces pumping losses and results in better mpg" ie warm air intake.

As noted, some of those intake and exhaust mods only work with old school, non computerized engines. Less restriction on intake or exhaust does not always equal better efficiency on modern computer controlled engines.

Here's what I've learned / thought about regarding this:
On a normal gasoline engine, increasing the efficiency of the intake/exhaust is going to have limited success (if any) with MPG improvement. The reason why is because of the way gasoline engines work: The ECU (or carburetor) in a very simplified form, just tries to inject the appropriate amount of fuel for the measured amount of incoming air, usually 14:1 ratio of air:fuel. If you increase the efficiency of the intake, that would allow more air into the engine, and more fuel, and make more power, and you'd accelerate. However... you may just want to cruise, so you close the throttle a little bit to compensate and... all your efficiencies from improving the intake go out the window, because the throttle body is (by design and operation) a restriction, and inefficient. This is one of the main reasons why diesels do so well, no throttle plate. If you improve the path of the intake, you end up having to compensate out the improvement with the throttle any, because you would accelerate too fast otherwise. Any improvements seen from optimizing the intake/exhaust are probably more happenstance and involve running slightly leaner, because the ECU (or carburetor) are injecting slightly less fuel due to one reason or another.

These are just my thoughts and opinions and real-world observations. Feel free to disagree

[awillard69]

I agree. My experience proves what you said, you just put it down in words.

My experience with a lower restriction intake ( I have 2 ) is better throttle response, which means improved acceleration. But there is no direct correlation with improved FE, IMO. If anything, it harms FE - at least with the lovely feeling of "right-foot-itis" - the power is fun.

Used wisely, one can briskly reach cruising speed, which can contribute to a FE improvement. Again, wisely using the performance capabilities of a vehicle to best FE advantage.

[jcantara]

Originally Posted by toomuch

I agree!
But nice post SVOboy.
I just don't understand how warmer air can increase efficiency.
However I have not done any research myself.
Since Cold Air Intakes take in denser air, which stuffs more oxygen in the explosion chamber, I guess it the computer puts in more fuel to compensate. Maybe that is why.
There probably is a whole thread on this somewhere, so sorry for not searching. I'll check later.

Here's my thoughts on this one, and it relates to my above post too:
The ECU (or carburetor) will inject an appropriate amount of fuel for any given amount of air (ideally, in real life it varies obviously, but that is the goal). An engine needs X mass of air/fuel to go a certain speed, regardless of the density of the air. If you are using less-dense air (hotter air is less dense) the engine will need the same mass of air to get the same amount of power, so you'll need to have the throttle open more (less restrictive) to compensate and allow in more of the air. There are other reasons why hot air is more efficient for cars, but that is probably the primary contributor.

[JohnnyGrey]

Carburetors add fuel based on the volume of air that rushes through them, but they don't on their own compensate for air density.

Warm air improves mpg because it promotes fuel atomization and allows for wider throttle openings per desired power.

Carburetors also do not compensate for air restriction. This is where air filter manufacturers pull their claims of improved fuel efficiency. A clogged air filter will cause a carbed car to run pig stinking rich.

An ECU in closed loop mode will maintain a 14.7:1 ratio regardless of how clogged the air filter is (short of total blockage). Whether your throttle plate or a dirty filter is providing manifold vacuum, your engine does not care, and is burning at 14.7:1 regardless.

[toomuch]

Thanks for all the WAI feedback.
This warm air thing seems to have no one single answer.
Here is my current summation:
The greater the temp of the air, the lower the density.
Lower density air has less molecules per volume.
Less fuel is needed to keep the 14.7:1 ratio of air to fuel.

Also, the WAI could just be explained away as magic. That is usually my answer in an arithmetic class. Stumps the professor every time . . .

[toomuch]

I will be starting a new thread on the topic of WAI & CAI. Please check it out.

[Gregte]

Originally Posted by toomuch

Thanks for all the WAI feedback.
This warm air thing seems to have no one single answer.
Here is my current summation:
The greater the temp of the air, the lower the density.
Lower density air has less molecules per volume.
Less fuel is needed to keep the 14.7:1 ratio of air to fuel.

Also as was mentioned by one poster, warm air helps liquid gasoline to atomize, i.e. become a vapor, and only vaporized gasoline burns. To the extent that some of the gas is still liquid at the time of ignition, it is wasted.

My understanding is that there is a delicate balance with any given engine design regarding how warm the intake air should be; warmer for some, cooler for others.