Seems to me that a tempering valve (mixes cold & hot water to lower the temperature for things like showers) would be an easy way to implement a bypass to control coolant temperature entering the engine.

The WAI debate is a little off topic, but it's interesting.

Wait a sec, shouldn't the thermostat valve be able to control the temp? Is it that the valve opens at a suboptimal temp? Or has a slow response time or too much hysteresis or isn't accurate or something?

Viscosity of the fluid does not mean the example is flawed. Air and milkshake are both fluids, so the same principles apply. In fact, he is correct- by creating a lower pressure in his mouth (i.e. a slight vacuum), the fluid is pushed *by the atmosphere* up through the straw. If you simultaneously sucked through the straw, and created a vacuum above the milkshake in the glass, no milkshake would go through the straw because the atmosphere is no longer "pushing".

In reality, the words pushing and pulling are interchangeable (although technically you are correct in the sense that fluids can only be pushed, not pulled). A fluid will move whenever there is a pressure difference- whether it is cause by one side being above atmospheric pressure, or the other side being below atmospheric pressure, (or both), is irrelevant. The higher the pressure difference the higher the flow rate. (Obviously a higher viscosity fluid like milkshake will flow more slowly than a lower viscosity fluid like air with the same pressure difference). In other words if you have a pipe, and you have 200 PSI at one end and 100 PSI at the other end, you'll have the exact same flow (given the same viscosity, pipe diameter, pipe length, etc.) if you have 100 PSI at one end and 0 PSI at the other end.

And as mentioned previously, the ONLY time you want cold air is for maximum HP (trying to cram as much air/fuel in the cylinder as possible). For all other driving conditions, hotter air (and fuel) will combust more completely and efficiently. That's true with pretty much any chemical reaction. More combustion =more power from the same amount of fuel and fewer unburnt HCs.

There are plenty of users on this forum who have proven that warm-air intakes (WAIs) have helped them.

You are right that you could reach a point of diminishing returns if you encounter knock retard. But for "economical" driving you'll never see KR. KR is typically only encountered during transitional situations (i.e. upshift / heavy throttle) and quick throttle position changes.

-BC

While strictly true, the practical effects can vary a lot with the properties of the fluid. Exaggerating a particular effect by reference to a more viscous fluid can be very useful for illustration purposes, which I'm pretty sure was the intention.

Same with thinking in terms of cold or heat transfer, in most circumstances (HVAC engineering uses the term "coolth" sometimes as an analog to heat). Or positive charge carriers or negative ones for that matter.

Your example is still flawed. A brisk run is akin to driving 100+ mph. I highly doubt the group here is interested in high speed, they are interested in cruising along in the right lane while fuel guzzling drivers zip by.

How about breathing through the same coffee stirrer while walking down the street?

See, the problem is a coffee stirrer will never be able to provide enough volume of a runner however. In the same way an engine at 1/4 open throttle can supply the volume of air for 100+ mph. However, it's more than enough for cruising.


Viscosity makes all the difference. If it didn't, why do people swith to a thinner motor oil like 0W20 from a thicker oil like say 10W40?

I wouldn't go from 10w40 to 0w20, but I have switched cars from 10w40 to 5w30.

-Jay

While having some insomnia last night I dug out my college fluid dynamics textbook and looked at the reduced air resistance theory for a WAI performance increase. Unfortunately, I'd need to know the exact geometry to be able to do anything detailed (assuming flow in a duct is not going to cut it). Then I'd probably need to computer model it (yeah, right - be easier for me to do empirical tests). While the valve will be open more, more air is required, so you have two competing effects. If the transition were quite sharp with a very nearly closed valve (so driving at low power levels), I would think the the change in resistance could be very significant. The difference between pretty far open (higher power levels) and slightly more than pretty far open would be much less.

So basically I didn't learn squat that helps settle anything. Helped me back to sleep though.

Well, if you can't do the theory research, might as well do applied research...right? :)

That reminds me of something from college. One of our class mates (an engineer) had his girlfriend leave him. He joked that at least she didn't dump him for a physicist. We replied that maybe she wanted more theory and less "hands on". :P

So are you saying that the laws of fluid dynamics apply only to fluids of certain viscosities?

-BC

air is air but computers are not some cars computers calculate air density by temperature on these cars a hot air intake will improve milage. If a car uses an air flow meter a hot air intake probably won't help. Before you say my theory is flawed I will say Look at my gaslog. I agree that cold air makes more power but on some cars Hot air makes more milage. On my car there is a map sensor and an intake temp sensor I installed a hot air intake (140f usually) and saw a 10mpg increase, I actually discovered the change when it fell off and temps fell to 78f. the difference between 24 and 34mpg in my car. Like always YMMV

I admit to being a little fuzzy on the particulars (especially since not all cars follow the same system), but doesn't the O2 sensor influence air intake settings as well? The idea is to try and maintain a stoichiometric fuel/air mixture so the catalytic converter can work (and minimize NOx emissions...I think), right?

Anybody have an idea how the different sensors interact in the control loop?

it does have a huge influence but at the same time hot air on my car affects timing oddly the MAP sensor on my car only covers idle and the WBo2 and IAT take care of the rest. Think about this a HAI will simulate driving through the desert and hot air is less dense needing less fuel to reach 14.7:1 ratio. Talking about power here is kind of pointless since a real hypermiler uses as little throttle as possible.

I think of it as needing more air to reach the ratio for a given amount of fuel. Hey, different strokes. :)

Let's assume that WAI does indeed cause the computer to gulp in more air, and further that the reduction in resistance from the more fully opened valve leads to a net energy gain even though more air is being pumped.

If that's the primary cause of efficiency improvements, it leads to an obvious design change: the air inlet valve. One that has less resistance at low levels of airflow. If it can matter so much, why hasn't been optimized previously? I can think of a couple ways of doing it just off the top of my head, so it can't be because it's impossible. Normally, I am hugely distrustful of "if it could've been done it would've been" arguments, but it's still a valid concern. That makes me wonder if indeed other effects are coming into play. The only air valve I've ever seen up close was for a DeLorean, and that sucker would've had much higher resistance at small opening distances. It had a movable disc (the name escapes me...diaphragm valve?) so air needed to turn a couple pretty sharp bends when mostly closed. Maybe given the way most people drive the benefits wouldn't be as great? Hypermilers do tend to drive at the lowest end of the power curve a lot more than ordinary folks. That might explain such a design oversight.

If I remember correctly DMC used Ford engines & powertrains. What you saw most likely was also placed in a Mustang and/or Cougar.

-Jay

Apparently they used a Volvo engine. Not that it really matters too much for this discussion. I hate DeLoreans anyway.

I think the main reason designers don't think about low rpm as much as we'd like is HP numbers sell. For the most part you need to spin the engine fast to make those numbers. My opinion on the throttle is a twin door affair so the air entering the engine always enters in the middle of the TB. If you were to combine that with a small plenum and runner intake you could effectively have the ideal milage engine.

Nearly everything on a car in the showroom is a design compromise -- designed to sell to the most people possible. That means power, excitement, noise, high RPM...at least from our point of view. If you ask on a high-performance forum, they'll tell you that everything comes set up for economy, boredom, quiet, low RPM. Either way, designs are also compromised for cost, reliability/longevity in all conditions with all drivers and driving styles, repairability (well, maybe not anymore), standards-compliance, regulatory compliance, aesthetics, and any number of other factors.

Fuel economy is important to car manufacturers. People want more fuel efficenet cars and the car companies must meet CAFE fuel economy standards.

So if warm air was more fuel efficient then why then do all car manufactures have the factor inlets OUTSIDE the engine compartment in an area where it could breathe in cool air? If warm are was more fuel efficient they would have the air intake inside the engine compartment to get warm air. Why spend the extra money to create an intake tract that breathes in cool air?

To get higher horsepower? I do think a WIA is a pretty wacky way to get better economy, but I'm willing to give it a shot.

Replacing my air valve would be a lot harder. Ditto for the engine.

That's a design compromise where they've chosen power over economy. You could also ask why they use automatic transmissions or ever-more-powerful larger engines when faced with fuel economy requirements. FE is not a higher priority than others, they do the minimum required to avoid CAFE fines or they accept the fines and build them into the price.

It's also for reliability/longevity/driveability in all conditions and for all drivers. A WAI could be problematic in abnormally hot climates and for people who drive hard -- as previously mentioned, detonation and timing and what not.

A WAI does not cause problems for most hypermilers in most climates.

It's like talking to a brick wall.

FACT: A WAI does not increase fuel economy.
https://www.metrompg.com/posts/wai-test.htm
https://www.techno-fandom.org/~hobbit.../results-1.txt
https://www.cleanmpg.com/forums/showthread.php?t=11462

For that one guy. He even discusses reasons it may not have worked in his tests.

It's like talking to a brick wall.

FACT: That link is to one guy's experiments with one car.

More links added for you.

In that third link states the guy had success when it was colder out. Call that a "maybe"?

What gets me is how cheap it is to give it a shot.

So, NovaResource has provided 3 examples. They're not perfect but they are examples. One admits that it's not conclusive, and another has mixed results depending on weather. The remaining one was on a Prius; I would not expect Prius data to apply to other vehicles.

How about the other side? Who can provide 3 imperfect examples of WAI being effective? I know I've seen many people post that it worked for them, but looking at a few gaslogs, it's not as clear as I remember.

Here's a google search of our own gaslogs:
https://www.google.com/search?q=site:...log+wai+OR+hai

Here's the "top 100" lists from our gaslogs:
https://www.gassavers.org/garage/viewall/epa (Top 100 improvements over EPA estimates)
https://www.gassavers.org/garage/viewall/mpg (Top 100 actual MPG)

Given that car design differences could certainly effect WAI impact, it makes real world data collection / comparison tough.

novaresource Have you done ANY experiments to back up YOUR claim that HAI doesn't work or are you just parroting what others say without proper experimentation? There is a wealth if experience here and to come in ad tell them they are all wrong is not wise.

I will run a back to back loop to prove or disprove on my car whether a HAI works or not. I have a 65 mile loop and I'll run one with cold air and one with the HAI and I will top the tank before each run so weight is not a factor. I will not fudge the results I will even take photos of my scangague to show what is happening. this will be a definitive test.


https://www.gassavers.org/showthread.php?t=10415

It occurs to me there may be some misunderstadings going on between the con/pro camps.

If your goal as a designer is to trade max hp for mpg, a WAI is a dumb way to go. The better option is to stick a smaller engine in the vehicle. My calling WAI a "wacky" method didn't really express this properly. :)

Also, the argument that the sort of driving that hypermilers do may not be optimized for is fairly persuasive to me. One need not look further than the tire inflation specs to find evidence of where the sales priorities lie.

Assuming that a valve design that has bad flow resistance at low flow rates is the culprit (and that's not 100% certain), why would they not change the design? The aforementioned not testing that regime extensively is one, economic considerations of manufacture are another. There is another possibility. Now, this last one could get me in trouble with my fellow engineers, but don't assume the designers considered every possible implication of their designs. I went to school with some engineers who were definitely mediocre. There's a bias among many to credit professionals with a minimum level of proficiency that may not be warranted industry wide. The effect is very pronounced among doctors. I've known too many med students! In fact I recently discovered my freshman year roommate wound up in medicine. Yikes. The flaw may simply have slipped through, not being flushed out by a testing process aiming at different goals. Of course some cars may not have the flaw. That would make testing results variable.

None of this proves WAI definitively works of course.

The time a WAI will help fuel economy is in colder weather while the engine is warming up. But it's not because the engine is getting warm air instead of cold air, it's because the engine is getting up to operation temp quicker. Once the car is up to operating temp the WAI is no longer helping. The fuel savings is not from a WAI but from a engine that gets up to operating temp sooner. This is why test results show little improvement and vary greatly with different cars. A car that warms up quickly on it's own will show little improvement with a WAI but a car that takes a long time to warm up normally will show greater improvement with a WAI.

This is the reason why older carbureted cars of the 70's and 80's had factory installed, vacuum controlled warm air systems. When the engine was cold, a flap in the air cleaner lid closed to block the cold air inlet and pull air in off the outside of the exhaust manifolds. As the engine warmed the valve would open to allow in colder air and block of the hot air. Another reason for this is that carbureted engines don't atomize the fuel that well. The hotter air helped with fuel atomization however, this is not a problem in modern cars with fuel injection.

Again, best fuel economy comes from a fully warmed up engine (warm coolant and warm oil), not warm intake air. You want a good idea for better economy? Install an intake system that pulls in warm air during startup when the engine is below operating temp but switches to cold air when the engine is fully warm. Another good idea: install an engine block heater and an oil pan heater to keep the coolant and oil temp warm when the engine is not running.

My mechanic thinks WAI is bunk too (well, he could see it at cold temps), FYI. He was making fun of me for removing my passenger side mirror too.

I tried folding the mirrors in on my truck on a long trip once. I didn't notice any difference in mileage.

-Jay

I thought about folding them! Mine have such a squared off shape when I do that I wasn't encouraged particularly. I've decided to run for a bit without it in and see if any difference is really noticeable. One mirror is a bit of a geek badge of honor, though.

Either that, or someone might think that you drove home drunk one night and broke it off...

-Jay

Why not conduct an experiment and try things instead of saying everyone is wrong. I try things that is why I'm getting 40+% over EPA ratings

Very good! That's why you need a professional looking cover plate.

Because trying something that you know won't work (and has been proven not to work by others) is a waste of time. If you would like to prove me wrong, be my guest.

Did you get a metal for that accomplishment? When you get to 100% over the EPA let me know. Until then, here's a cookie for you.

https://thehealthblogger.com/wp-conte.../07/cookie.jpg

My browser blocks cookies. :)