New Idea - Hot Box Intake

[Zerohour]

Well I'm gonna borrow a few ideas from a few places and try to tagged the altogether on this one. I know a few people have "Hot air Intakes", which help their mileage to constantly feeding hot air into the engine. I view this as both good and bad.

With fall soon approaching I won't get 80 degree mornings. And in fact we're going to break 50 this weekend with the cold front/hurricane off the east coast.

So this is my idea:

1) Snake metal flex pipe, or metal hard line from the exhaust manifold region to the air intake (this I take from Triumph TR7)
2) Use a universal door lock actuator to open a port on the exhaust intake box. (this I take from a post I read on the "variable air dam")
3) Wire the actuator two a switch and a indicator light.

While it might take the drive train some time to warm up, I think this will aid the engine on the coming mornings of fall and winter. But once up the temps, I can close it off and keep pulling the clean air to keep the engine running at normal temps. I don't want to temp fate with an air block and a Hot air intake.

Post some feedback. Haven't done any background searches, or parts ordering. Just an idea.

[techanic]

I'm confused. The last I heard, we wanted cold air as it was more dense i.e. more packed with oxygen. Now I keep reading about hot air. What is the benefit of hot air, how can it increase mpg?

[Zerohour]

most engines have a ranges of temperatures at which they work the best. Most engines do not like to run "cold". This is why you would normally have a "180 degree thermostat" and not a "100 degree thermostat". The engine needs to retain a proper amount of heat to run efficiently. Pull hot air into the intake helps warm the motor faster on cold days.

And if you weren't aware, many, many cars have an antifreeze pipe running through the throttle body or throttle plate to keep the TB warm on cold days. I've been told this is because throttle bodies would "Freeze". But thats more likely an old wise mans tale. Its there to warm that throttle up and keep the temps up during cold starts. Convection occurs really when there is large difference in temperature. So on very cold days, the hot coolant in the TB transfers to the air much better than it would on warm days. If you don't believe me, I've got a test for you to run with your morning coffee. :-p

This relates to why there are Smog pumps / Air Pumps / EGR Valves. While at full temp they recycle some exhaust gas, but in cold conditions they are "fully open" and recycle large quantities of unburnt gas.

It is true that cold air is more dense, and will give you more potential power. But you need to think of the overall systems at work. There is a reason you have mutliple sensors on the engine including Mass airflow sensors (MAF) / MAP ( Air Pressure) / Speed Densisty Sensors and air temp intake sensors, combined with your readings from the other bits like a knock sensor, oxygen sensors, transmissions readings with automatics, The computer in your car uses tables of numbers to determine what is the best Air/Fuel ratio to maintain, if it should shift, how much the emissions system should recycle, etc. Its basically what makes a modern car that much more complex.

But basically the idea is to get the car up the temp sooner, and on very cold days help to keep it running warmer. If you're new to tracking your gas mileage you will soon see those numbers drop off come the fall as the days get cooler.

I see that you live in Texas, so depending where you are, you may have never try to start a car at below freezing. Here in Pennsyltucky we aren't the coldest state, but we do get periods of time where the temperature will not break freezing.

Even that being said, there is still a fuel economy (FE) difference between 45 degree weather and 95 degree weather. That variance will be ~10-15%. Its much worse if you're driving short distances.

Also, in the cold we need to run the defroster, which takes an additional 10-11% off my Subaru's FE. So if its really cold, and I'm defrosting the windows, I loose 15% FE due to cold: 25MPG-> 21.25 MPG (this is accurate I get ~20-22 in winter) And then if I need to run the defroster it pulls an additional 10% off FE: 21.25 MPG -> 19.125 MPG. And this is about spot on with my worst tank last winter. Right after graduating school, and not working, I only drove short trips around town in the cold. The worst tank I had was ~18.7MPG.

And thats why I would like to build a hot box for the Subaru's intake!

[brucey]

Zerohour: I've simply removed my intake tract that is sucking air from the grill so now it sucks from the back of the engine bay. This saves a lot of engine clutter and does help it get up to temperature faster. There is no real need for the intake tract other than as a silencer on heavy throttle, but hell I like the noise. The extra availability of that side and the engine bay are a bonus on top of just the increased warm up times.

[Zerohour]

I had a short ram air intake setup before, but I had a box and used the front air intake piece. It made a notable difference one hills. But in the since that the engine would flat at a higher speed. I guess I could swap it back to the modified intake and modify that one to pick up heat.

Do you have a picture of yours?

[brucey]

Not directly but visible here:



Just the intake tract removed but the filter kept. That's how my engine bay has been.

[redyaris]

Techanic; as I understand it,
The volume of the cylinder is constant, so the same volume of air enters the cylinder no matter what the throatle position. So what does the throatle do? it changes the mass of air entering the cylinder. So the density [mass/volume] of the air in the cylinder when the intake valve closes is controled by the throatle. So what else changes the density of air? Temperature, as the temperature goes up the density goes down. there are two other benifits to higher air temperature; mixing of fuel:air and combustion efficiancy. when looking for fuel economy we drive at very low power, so the throatle is almost closed, so by heating the air the thoatle can be opened a little more thus redusing pumping loses, caused by the throatle being almost closed. High power needs high density air, and lots of fuel, low power needs low density air, and very little fuel.

I hope this helps

[adeadhead.skip]

Zerohour: What you propose is standard on most vehicles I owned (Fords & Chevys) since the 70's. They basically all work the same: A cowling around the exhaust manifold, a metal hose between the cowling and the air filter housing, and a thermostatic valve in the air filter housing.

The valve in my current daily drive (Chev) is a simple mechanism. A flap directs air from either the cold air intake or through the preheater hose (metal flex). A sealed wax cylinder closes the flap to the cold air intake when cold, directing the preheated manifold air into the filter housing. As the air warms up, the wax melts, the flap opens and the colder air flows freely. Simple and effective.

You can exclude the door lock mechanism. switch and indicator by picking up a thermostatic filter housing, cutting out the valve mechanism and adapting it to your intake setup.

Some older versions were vacuum assisted and prone to failure. The current setup works well.

[Zerohour]

@ adeadhead.skip

Hmmm can you pickup one of these from the parts store, or is this part of an intake box? I've only familiar with the vacuum assisted ones (from a TR7). I was born after carbureterred motors, so most of my experience comes from new engines without heat induction intakes.

Could you post some pictures of yours? I might have time to wander through the salvage yard and find something this coming weekend. I'm looking at using the door lock mechcanism for ~$8 bucks. So its pretty cheap. and I have a throttle body laying around I could use if I remove the spring. I haven't really laid out proper plans yet, so I might take you up on your idea provided I find it more cost effective/simpler to build!

Does your warm air inlet come from your K1500 pickup?

:-)

[Olympiadis]

I have a similar truck. The flapper-valve is integrated into the air-filter housing. It is simply designed to speed up the warm-up cycle, then maintain a relatively consistent air temp in order to help keep emissions within a more predictable window.

You are better off using one that is vacuum or electrically operated for ease of control.