Heat riser or butterfly is designed to spring load open and allow exhaust flow thru but .. as time goes on they jam or restrict air passage.
Used on Small Block Chev from 62-78.
- 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
.jpg "55 Chev Bumper : Rear Over rider set w/ Hardware")
.jpg "Fuel tank Sender Unit: 68-74 Corvette")