The Borla Flow Restrictor

Borla exhaust systems for the ZR-1 have a flow restrictor located just before the resonator. It's in the down stream end of the pipe that connects to the exhaust manifold. On the right and left sides. It is not located in the resonator. It's probably there to tune the sound of the exhaust system. Back-pressure is a common muffling technique. I have found that removal of the restrictor has little effect on the sound of the exhaust. We normally remove the restrictor when installing headers. I have found that as back-pressure is reduced power always increases. The LT5 likes to have back-pressure as close to zero as possible.

The picture shows the 1.90" restrictor after it has been removed from the pipe. Extract the restrictor by cutting 1/4" off the end of the pipe. This will remove the welded connection, the ring at the left side of the picture. Then the restrictor should easily shake out of the pipe.