warm air intake mod ('98 Civic HX)

[DonR]

Tee a heat riser pipe from exhaust manifold heat shield, or from behind the radiator into the intake infront of the filter. A butterfly valve on either the hot or cold side can be used to control temps. Carbed cars used a bi-metal thermostat controled, vaccum operated valve. But if you want you can use a TOGGLE SWITCH to control an electric solenoid to open & control the valve.
You could use the exhaust heat as the continuous heat & the electric heater for instaneous heat.

[jonathan150cc]

Why not just somehow type into the heat off of the exhaust manifold?
My Saab 900 had a factory setup that did exactly this. You can simply duct your air filter housing to an area near the exhaust header with some dryer exhaust tubing.

[max_frontal_area]

why are you preheating your intake air, is the AT 30f below?

[stevey_frac]

Originally Posted by max_frontal_area

why are you preheating your intake air, is the AT 30f below?

Hot air does two things: It lowers the density of air, meaning you have to have your throttle more open to to get the same mass of air, which reduces pumping losses.

It also increases the temperatures of the air going in. Now i know that's obvious, but it's important. Most thermodynamic cycles improve efficiency at higher temperatures.

[Wonderboy]

Im using a modified intake with a cone filter, and I do agree that the best option is using exhaust heat...

However, first of all I can't switch it on or off like I can a glow plug. Also, I want to keep a short ram intake design, I want to avoid the power losses that come from snaking an intake hose all around the engine bay. The way I have it now its almost a straight shot.

Isn't the point to sacrifice power for efficiency? I have an extra hose made of heating duct extending from my stock intake filter box to the exhaust manifold. intake air temperature rarely eclipses 150F, and normally sticks around 130F. I blocked off the stock pipe that comes from the bottom of the filter box with a plastic bag. This plus my aero mods (skirts, grille block, mirror delete) saw an 8 - 10mpg increase. I haven't done an A-B-A test yet, but I think it may have worked. I really think you should stick with the stock intake and the MAF sensor... I'd wager to guess your lean burn isn't working as much as you'd like as a result of the absence of the stock intake setup. Just pipe it to breathe right off your exhaust manifold and see what happens. You don't have anything to lose with how easy it is to try.

[LeanBurninating]

Current intake setup:



I like it this way versus stock because I am sure it flows easier and there are no big sound boxes. I just put this one on tonight, Im going to see if my numbers changed from the one that I swapped out (basically the same thing, except all pvc, no metal, and smaller inside diameter) and sooner or later I will try the stock intake again.

I will also cap off those air ducts from the bumper towards the filter, nice call wonderboy.

On a side note, do you think it will make much difference to relocate the breather hose and temp sensor? Will putting them further upstream yield less turbulence at the tb?

[LeanBurninating]

I am thinking that a glow plug will make too much heat, and I just know that Im accidentally going to leave it switched to "on" and just melt everything.

I know you are all not fans of using electricity for heat, but can you at least help me brainstorm here?

What about a cigarette lighter element(s) ? Enough heat? too much current? thoughts?

I mostly want to avoid anything melting off and flying into the engine....

Thanks people.

[dcb]

A few people have tried after market filters, they didn't help mpg
Testing a 'performance' air filter for MPG - Part 2 - MetroMPG.com

I do think using EXHAUST heat to offset throttle losses has possibilities , consider:
# At 0 °C and 100 kPa, dry air has a density of 1.2754 kg/m3.
# At 100 °C and 100 kPa, dry air has a density of 0.9336 kg/m3.

Not that all cars like hot air (possibly a software issue), but if yours does then if you can swing the temperature (about 100 degrees C just for example) as needed then you can basically "detune" the engine. Ok, so what you say.

Well the effects are compounding here. Your (gasoline) engine is least efficient with the throttle closed, if you are on the hiway and you are not quite at bsfc peak because of insufficient load for the engine, if you add heat, then:

1. the air going across the throttle plate and through the engine becomes less dense, therefore less restriction (1/4 less restriction in the example figures).

2. Because there is less air mass moving through the engine, you can (perhaps should) open the throttle more, reducing losses further for a given power output.

Now I have not thought enough about it to see if it affects peak bsfc rpm in a general manner, assuming an ideal ECU.

But as far as electric for heat, and why it is a bad idea, do the math, Here is your homework assignment:
1. Determine the mass flow of air you want to heat up (say, cruising the hiway)
2. Determine how much you want to heat the air
3. Determine how much power (amps*volts) you need to heat the air the desired amount.
4. Multiply that power by alternator/belt losses to determine how much power you are taking from the crankshaft (when exhaust heet is "free").

[dcb]

(another approach)
lets say you have a 2 liter engine, cruising at 2000 rpm. Lets also say the throttle is not very open for a %30 Volumetric efficiency. And you want to raise the air temperature 50C degrees.

So your engine is trying to move 1000 liters per minute, but the throttle is limiting it to 300 liters per minute.

Lets say a litre of air is 1.2g/L, so you are trying to raise 360 grams by 50C, every minute, which requires 18000 calories (not kilocalories).

Lets say (after some more googling) that a calorie = 3.08596003 foot pounds (yay), so we need 55547 foot pounds per minute worth, or 926 foot pounds per second.

Well, a horsepower is 550 foot pounds per second, so this heater requires 1.7 hp for input, so if your alternator is (swag) %85 efficient, you will be taking about 2 HP from the crank to run this heater.

A general rule of thumb is that your (not huge) car only needs about 10-15 hp to maintain speed on the hiway, so 2hp is a very large chunk of power just to run a heater (when exhaust heat is free). You will need to draw almost 100 amps for this example.

[Wonderboy]

Holy ****, dcb. That sounded like a heaping dose of reason. Impressive. I'd probably halt my electric air heater project right there, LeanBurninating. He's made of reason. Another theory I have (may or may not be true) is that the ECU is looking for some very specific parameters, one of which HAS to include MAP (Manifold Air Pressure). By "increasing" the flow with a cone filter, you are lowering the very specific pressure parameters the ECU expects, and may also be a reason you don't get lean burn as much as you want. If there's someone who knows the real answer to this, please shed the light!