Chrysler (and the others) got it right 50 years ago.
The air cleaner snout has a diaphragm (vacuum-operated) flap with 2 positions:
1. is open to a duct leading to the radiator support, and allows ambient only.
2. is below the snout, selected by the flap closing, and admits pre-heated air passing over/through a shroud over the driver's side exhaust manifold.
3. what temperature the can's interior sees is determined by a thermal vacuum switch inside the can. When the engine and underhood temperature is low (cold day, cold start) it admits only pre-heated air until the can interior temperature is 150 degrees (?). Above this, it blends cold air to keep the temperature nearly constant for best mileage and accurate mixture.
4. in addition, low engine vacuum (WOT) opens the flap and admits only cold air for max power regardless of can temperature.
Other than a larger snout, this idea still works perfectly with very few components.
