[elhigh]

Reducing airflow through the radiator doesn't do anything to the engine's rpms, it only permits the engine to reach operating temperature faster, and thus enter closed-loop operation which is more efficient than the open-loop operation. In Fuel Injected World, open-loop is the same as running with the choke on in Carbureted World - necessary but wasteful, so you want to get out of that state as quickly as possible.

The other point behind reducing airflow through the radiator is to get more of the air flowing around the car where the flow is smooth and less draggy. Allowing only enough air as is necessary for cooling will reduce how much air gets introduced to that craggy, not-streamlined lump of iron and then dumped to the similarly high-drag region under the car.

The engine's rpms are not affected by the engine's temperature at all. The driver controls that, influenced by his desired road speed and the gear he has chosen.

Keep thinking, though. A sealed engine compartment with a remote radiator has been done before to great effect. Now, if we can just make that happen on one of these Metros or some such...