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Can anyone think of a clever way to use exhaust manifold heat (which appears very quickly after start) to help other stuff warm up?
Maybe some kind of heat exchanger? Closed loop of fancy synthetic heat-resistant oil that could handle exhaust temps. Oil/air heat exchanger in the exhaust flow (or wrapped around the exhaust pipe), connected to an oil/water heat exchanger in the coolant loop. Complicated, expensive, and probably heavy.
OTOH, small airplanes (and some cars) have heaters that pull warm air off the exhaust manifold, so you could eliminate the heater core loop (maybe 1qt. of coolant, heater core and hoses) and get nearly instant heat. Have to figure out a way to monitor for exhaust gasses in case the exhaust system starts leaking. Dash-mounted CO sensor would handle that, I think.
It would require ductwork from the manifold to the HVAC intake port, and wouldn't pull heat on recirc, but heat and recirc don't usually get used that much together anyway. An intrepid ecomodder should be able to handle a little more adversity than the typical car buyer, so maybe it would work.
I suppose it would create a theoretical increase in the length of time it takes the catalytic converter to warm up and start working, but I doubt it would be significant. Relative to heating up a cat to operating temp, warming the cabin seems like pretty small potatoes.
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