bb_66

Is it necessary to wire open the exhaust flow valve if the hot slot holes are plugged on the intake manifold? 427/390hp

tbarb

The hot slot holes feed off of the exhaust heat that travels through the cavity under the plenum in the intake manifold. The spring controlled heat riser forces exhaust up through the intake so blocking the hot slot under the carburetor is very good but to completely stop the flow of exhaust heat through the intake manifold wire the heat riser valve open.

With a cast iron manifold in cold weather the exhaust heat is your friend.

bb_66

Okay, so no issues regarding back flow into a plugged intake if I leave it to the spring to open the valve?

dugsgms74

No, no issues. You only need to wire it open if you completely block off the crossover(block the passages where the manifold meets the head), just blocking off the hot slot holes does not require wiring open the heat riser valve.