Simpson Race Exhausts Stainless Steel 4-1 Exhaust Manifold suitable for Ford Crossflow engine.

Bore at flange that meets the Cylinder Head is 33 mm.

About Simpson Exhaust Manifolds
All Simpson manifolds have been run on the Dyno and proven to increase horsepower and torque. Simpson manifolds are built to the engine builders specifications. Every branch of the manifold will be of equal length. When building manifolds they use tags and springs to hold pipes in the collector. Not only does this look better it's also more reliable than using any bolts or standard wire.