GM article from 1954 regarding the
235 Corvette Exhaust Manifold Heat Control Valve.
The basic exhaust manifold design consists of two outlets instead of one,divided by an internal wall at the rear of the heat box.
When using the manifold heat control valve, the exhaust gases from the front three cylinders are directed to the heat valve in the heat box.
Part of these gases are then directed by the valve to the intake manifold to preheat the incoming charge during warm-up. This portion of the gases then rejoins the original stream to be expelled through the front exhaust pipe, right hand muffer and tail pipe. The exhaust gases from the rear three cylinders are carried away by the rear outlet and expelled through the left hand tail pipe.
However, it has been determined that manifold heat control valve operation is neither necessary nor desirable under normal temperature and operating conditions encountered with the Corvette.
Consequently a manifold heat shield has been installed between the exhaust and intake manifolds to direct exhaust gases from the front three cylinders away from the intake manifold, thus eliminating preheating of the incoming charge.
Also, the heat control valve spring has been reversed so as to hold the valve continuosly in a "heat-off" position.
If preheating of the incoming charge is desired for extreme cold weather operation, it will be necessary to remove the heat shield and reverse the heat control valve spring.
