My 2 cents on this topic:
Neither coolant or exhaust heat provided thru tubes from Fenton headers do anything at all. Extensive testing with an infrared thermometer tells me the cylinder head warms and stabilizes intake temperature via the intake runners and this peripheral stuff is just too slow. I'm engineering a heat plate for a friend's 292 with offy 4 barrel intake that will use diesel glow plugs to perform the required task instantly and turn off as soon as heat migration is underway. That was basically the secret to the stock thermostatic system.
