All about hot air...

[theholycow]

How to EOC:

1. Declutch or shift to neutral and turn key to "Off".
2. As soon as engine has stopped turning, turn key back to "On" but don't start it.
3. When you're ready to restart, put it in 5th gear (or a lower gear if you're going really slow, but I think most cars will start in 5th above 20mph) and bring the clutch pedal part-way up, like you're trying to hold the car on a hill. Don't wait for the engine to fire up, just let it kick the engine over for a moment, then step the clutch pedal back down to the floor. The engine will start.

On forum subscriptions:
You can subscribe with or without email notifications. It should work fine. You can change your user options to automatically subscribe to threads where you post (although that won't work when you use the Quick Reply box).

This forum has just the right amount of traffic that I've just bookmarked "View Recent Posts" and I check it a few times a day...no need for me to pick certain threads to keep up with, I visit them all.

[move]

About hot air, more specifically intake manifolds. They are definitley hot. Hondata did an intake manifold gasket that isolated heat transfer to the manifold and gained some power, so it is obvious that a colder manifold makes more power. A hot manifold should heat up the air for more efficienty. OK, so far it's hot and cold, but what impresses me most is the way this thing works. At low load/low rpm where you want mpg, the air moves slow and it has time to heat up, so you have mpg, at high load/ high rpm where you want power, air moves fast and it dosen't have time to heat up, so you have power. It's BRILIANT (i think). The intake manifold temperature could be a tuning tool betwen mpg/power without compromising to much. I have seen old cars with 2valve/piston with intake manifold casted togeder with the exhaust manifold, so this could be taken very far. But before that i would like to hear your opinion on this.

[1cheap1]

On my twin tubo car I want denser cool air to make max power. The hotter the air the less dense it is, the less power. For this car it is all about power, not mpg. It gets about 13 mpg ( my foot is in it all the time). For me fall and winter and early spring means more power, summer not so much.

[theholycow]

Speaking on intake manifolds getting exhaust heat, the Early Fuel Evaporation system on my 1980 Buick pumps exhaust through channels in the intake manifold when the engine is cold to make it warm up more quickly, partly for driveability and partly for fuel economy.

[Project84]

I stopped caring about the science behind it and/or proving/disproving the theory that hot air works to increase MPG. You're driving a Saturn S-series... IT WORKS... VERY WELL.

Go to my garage and read up on my SL2 which is now retired if you want more info.

/thread

[theholycow]

The science is important for these reasons:
1. To help convince people to try it
2. To develop related strategies and technologies that might apply to other vehicles that don't work with it

However, results are certainly a good thing on their own!

[koji_kabuto]

we all know what hot/warm air does to the engine. there are factors that are being overlooked when it comes to saving fuel. i know some but im pretty sure you guys have more.

transmission: preferably low gear ratio. having lower rpm during cruising makes it harder for the engine to maintain rpm, in return engine load increases and so we call that throttling. if a high gear ratio lets you cruise 4000rpm @60mph, peak torque is near the powerband and maintaining or even accelerating is easier, meaning high vaccum/pumping loss. also consider 4000rm on a 4 cylinder is like a v8 cruising @2000rpm if we were to relate them. the power/cfm/afr might be the same given the instance. and friction is also higher...

displacement: overly large displacement will not yeild any improvement on wai/hai. engine is too powerful to maintain high loads during cruising. very small displacement will almost gain nothing since load is kept constanly high during cruising. i would choose a displacement of 2 to 3 litre if i were to practice wai/hai.

one example i remember is mr. serntraSE-R's scion xb. massive drag coefficient, 1.5ton weight and 1.5 litre engine. he did a lot of tests and unfortunately didnt gain anything.

tuning: megasquirt is not very expensive or used aem ems wiring is not very complicated if you were to convert them.. lean the engine out up until bucking and missfires, then increase the timing. ive tuned some cars that gained 20-40% fuel economy. in my car with a 4.4 final drive and awd i cant gain any as much as i did with my old transmission (which was 4.0) no matter how much i tune the engine. so meaning you can only do so much given the factors that ive noticed.

[Sludgy]

The cold / hot air answer boils down to two facts:

1. At Wide Open Throttle, an engine drawing in cold air will produce more power and will use less gas per horsepower. The "Brake Specific Fuel Consumption" is less.

2. Automobile engines hardly ever operate at WOT. They are throttled under most conditions. Warm (less dense) air reduces the work an engine has to expend to draw air across the throttle. This improves real world mileage. EGR has a similar effect.

[theholycow]

I agree that at WOT cold air with produce more power, but why would it use less fuel per horsepower?

[Project84]

I think since Saturn S-series see widespread success and they are one of very few vehicles people try to hypermile in that only uses a MAP sensor, it really comes down to does your car have MAP or MAF? MAP = success w/ HAI, MAF = won't make a difference because the engine is going to retune and adjust to the increased intake air temps.

Scion xB = MAF
Saturn S-Series = MAP


MAF is much more complicated and MAP is kinda bare essential.

This is usually easy to see which one you have. If there's a sensor with either honeycomb looking stuff or a wire running through it in your intake tubing before entering your throttle body, you've got a MAF car and you shouldn't waste your time with a HAI. That wire reads the mass of the air in relation to temperature of the air and adjusts accordingly to keep your engine runnings at factory set levels..... you cannot trick this sensor or avoid using it without extensive work.