3 Bolt Flange Reducer

Just pick the reducer size that matches the diameter of the header collector. Bolt it to the collector ring, and weld on the tailpipe. If you have a header without the collector ring, use Hooker slip–on reducers. They're sized to slip over the collector and weld to the exhaust pipe.

Super Competition Reducer, 3 Bolt Flange, 3.5" OD Collector to 2.5" OD Tailpipe, One Pair