Exhaust Heat Riser: Chev SB V8 64-78 era VariousThe heat riser, also known as a butterfly valve, is engineered to spring open and permit exhaust flow. However, over time, it can become stuck or impede airflow. This part fits Small Block Chevrolet engines from 1962 to 1978. Camaro 67 78 Impala 54 78 Corvette 64 78 Chevelle 64 73 Nova 64 68 Monte Carlo 70 78 Used on most GM light trucks and vans with SB Chev V8