You would need to dismantle a stovebolt intake/exhaust manifold assembly to see the exhaust gas routing. There is a flap valve that directs the exhaust against the bottom of the intake manifold when the engine is cold, helping to warm the intake mixture and keep the gasoline vaporized. Once the manifold heats up, the bimetal spring relaxes, gravity takes over and pulls the weight, and the flap valve down, and the exhaust is directed away from the manifold and straight out the exhaust pipe.
On a V-8, the heat riser partly blocks off the outlet of one exhaust manifold, and directs some of the gas up through the center of the cylinder head, under the carburetor, and out the other side. Early models had the same bimetal spring/weight combination as the 6-cylinders, while later heat risers were vacuum-operated, using a thermal/vacuum valve and a vacuum motor to open and close the heat riser flap. Those valves are called "E.F.E." valves, (early fuel evaporation). In either type of system, the exhaust gas is routed right against the intake, to keep the fuel vaporized during warmup.
Another type of exhaust heat system involves pulling fresh air through a passageway in the exhaust manifold, and applying it to the automatic choke in the carburetor. This is called a "choke stove", and does not involve routing the exhaust to the carburetor, just heated air.
Jerry
