The manifold heat valve forces hot exhaust gases up around the base of the carburetor and the intake to warm fuel/air mixture to optimum operating temperature. If conditions are too cool, the gasoline can condense back into a liquid as the air/fuel mixture comes into contact with cold engine components, resulting in a mixture that is too lean. Lean fuel/air mixtures can cause rough idle, hesitation on acceleration and stalling. As the engine warms to operating temperature, the heat riser valve adjusts to keep the air/fuel ratio at the correct temperature giving you the performance you demand. These valves are manufactured according to factory specs and are available for both small block and big block applications.
| Make | Model | Years |
| Chevrolet | Chevy II | 1967 - 1968 |
| Chevrolet | Nova | 1969 |
