Heat soak into the carburetor is what causes percolation and hard hot restarts, especially on a dual-plane manifold sitting over a hot lifter valley. An insulator gasket puts a thermal break between the two. The divided center matters: it maintains the manifold's plenum separation instead of connecting the two halves, which would alter how the engine breathes.

Edelbrock 9266 Heat Insulator Details:

• 0.320 in. thick nitrile rubber composite insulator.
• Square bore shape with a divided center to suit dual-plane manifolds.
• For four-barrel carburetors.
• Reduces heat transfer from the manifold into the carburetor body.
• Sold individually. Note this part is a gasket, not an electrical relay.