Cold air vs hot air....

takza · Post by **takza** » Thu Nov 17, 2005 4:51 am

http://cars.rasoenterprises.com/Carbs-IntakeHeat.htm

"Keeping the heated air supply to the carburetor from the temperature-controlled air cleaner will help with fuel vaporization under cruising conditions. This device utilizes a hot air shroud around the exhaust manifold and a duct to lead warm air into the air cleaner. A thermostat in the air cleaner maintains (or attempts to maintain) a constant temperature to the carburetor. Although this type of air cleaner is probably more restrictive than a open element air cleaner, your gas mileage will probably be slightly higher with it. This type of air cleaner shuts off the hot air when the engine is accelerating (low manifold vacuum ~ 5" HG) and this is the time when the hot spot in the intake manifold is especially useful."

brianp · Post by **brianp** » Thu Nov 17, 2005 7:48 am

Yeah, the tercel has a hot air return (at least mine does) it is an aluminum tube going from the engine to the air filter.

yam yam · Post by **yam yam** » Thu Nov 17, 2005 2:37 pm

Hmm, I'm guessing thats what our HAI tube is for.

I dunno... Usually I noticed the HAI flap closed only after the car is fully warmed up, but it never opens up to let in hot exhaust mainfold air unless the little vacuum operated temp sensor cools off a bit. If I pop open the air filter cover, and put a little water on that sensor to speed up the cooling, you can see the flap pop up... Interesting though.... I always thought, you know, hot air first to facilitate a quicker warmup period, and then cold air for better fuel combustion and such....

Typrus · Post by **Typrus** » Thu Nov 17, 2005 3:43 pm

Too cool of air will kill combustion as it will cause the fuel to recondense. A vapor combusts FAR better than little liquid globules.
Cooler air is denser. Thus, more oxygen per air.

Its a crucial balance that SHOULD be maintained.

morgsie · Post by **morgsie** » Thu Nov 17, 2005 8:04 pm

I'd say the only advantage to this is when starting your car. The faster your engine warms up, the better for fuel. It's some low percentage of fuel that actually gets burned when running cold (i think it's like 25% or some thing). I know GM has had a system like this since the 70s (maybe even the late 60s, im not sure on that). Once warmed up cold air is better, period. Why do you think people have cold air intakes, ram air, intercoolers on turbos, hood scopes, etc etc?

The vavle on the air cleaner should be closed when the engine is cold (getting vacuum) and then open once at operating temperature (no vacuum). AS for too cool of air, i dont know how cold you're taking about, but i lived on the canadian parries for 8 years and some cars seemed to preform better in colder conditions. Once warmed out mind you.

Typrus · Post by **Typrus** » Thu Nov 17, 2005 11:09 pm

I think it applies more to carburetors than FI. In carbs, the air is likely still cold by the time it hits the barrels. In FI, it's likely warmed up a bit by the time it nears the injectors.

Mosquito · Post by **Mosquito** » Mon Nov 21, 2005 1:35 pm

brianp wrote:Yeah, the tercel has a hot air return (at least mine does) it is an aluminum tube going from the engine to the air filter.

Just picked up my Tercel this weekend, ran a little rough, and just eyeballing the engine I noticed that tube had become undone. Reattaching it was my first "fix"--it's run much better the first few minutes since then.