switchable cold/warm air intake

[oilyriser]

A few weeks ago, a guy was telling me about his old car where you had to move a lever in winter to divert warm air into the carburetor, to help the fuel evaporate. He said in winter, it let the car start easier, and in summer it gave better gas mileage, so he kept it that way all the time.

Modern cars don't need this device to start in winter, but now I'm wondering if one might still give better gas mileage during summer.

Preheating the air from 20 C to 100 C with engine coolant would reduce the engine's power by about 22%, but maybe it would give a few % better gas mileage. If I wanted to have full power, I'd simply switch off the flow of hot engine coolant to the preheater.

I have to check my car to see if everything would still work properly if the intake air were heated to 100 degrees C. This is another experiment I'd like to try.

 

[Shannow]

Oilyriser,
The old G.M. set-up had an adjustable bimetallic strip which controlled the vacuum applie to an actuator, which controlled air inlet temperature.

I was mucking around with that (there was a mechanic, John Bennet achieving some remarkable things down here with propane, using inlet temps).

Ended up getting 25/26 MPG out of a 253 c.i. V-8 auto wagon, with a bit of fiddling.

Bear in mind this was with a quadrajet, so where the idle/off idle mixture feeds, and the other ports makes soe difference.

Hot inlet air (70-80C), PCV routed through a heat exchanger (copper pipe wound around one exhaust manifold, wrapped in ceramic fibre), a continuous 2mm diameter EGR bleed (once again, directed at the idle ports).

Fuse wire partially restricting the idle fuel ports, and a thermostat that controlled the coolant inlet temp to the block.

At full throttle, vacuum drops, and starigh cold air feeds the carb...a little transitional pinging, but nothing much.

 

[oilyriser]

I could find one of those old vacuum operated flap valve things at a junkyard, so the flap could switch with low vacuum. Though I'd have a bit of trouble getting hot air from around the exhaust manifold on a Subaru, since it's on the bottom. But even if I tapped into the coolant going to the heater core, and didn't have a valve to switch it off during acceleration, the simple fact of increased airflow would result in lower air temperatures. The power loss wouldn't be as bad as I first though.

I'd want to have way not to cook the stuff connected to the intake tract. It's probably rated for 100C, but keeping things cool normally makes them last longer. Maybe a combination of an old vacuum operated air valve, and a small heater core supplying the warm air, would work.