It's a HEADER FLANGE. It bolts to the exhaust side of an engine cylinder head. Thin-wall metal tubes are welded to the flange. The tubes go together at some length (usually between 12- and 36-inches) which then connects to the exhaust pipe. The completed part is called EXHAUST HEADERS. It replaces the exhaust manifold (usually cast iron, very restrictive). The metal tubes will have a TUNED LENGTH which is designed to increase engine power at a specific RPM. Short pipes are for low RPM, long pipes are high RPM. This flange looks like it's for a Mitsubishi 4G63 engine.

It's a HEADER FLANGE. It bolts to the exhaust side of an engine cylinder head. Thin-wall metal tubes are welded to the flange. The tubes go together at some length (usually between 12- and 36-inches) which then connects to the exhaust pipe. The completed part is called EXHAUST HEADERS. It replaces the exhaust manifold (usually cast iron, very restrictive). The metal tubes will have a TUNED LENGTH which is designed to increase engine power at a specific RPM. Short pipes are for low RPM, long pipes are high RPM. This flange looks like it's for a Mitsubishi 4G63 engine.

Honda Civic / Acura Integra B16 B18 (DOHC VTEC MOTOR) manifold spacer. mounts between the following manifold and head to allow more clearance between engine block and turbo exhaust. see second link for actual item...Performance Exhaust Manifold Flange

References:

http://www.amazon.com/Rev9Power-Rev9_MF-072-Integra-Stainless-Manifold/dp/B00...

http://www.jegs.com/i/Vibrant+Performance/231/14610D/10002/-1

Reason:
Another opinion was accepted instead.