Oldsmobile 400 425 455 MID-AIR™ MidRise Aluminum Intake Manifold [Black] Due to the large-diameter 13

Due to the large-diameter 13 in

Its unique construction features an aluminum core with an outer silicone coating

Speedmaster cylinder head fasteners are made from aircraft quality 8740 high tensile strength chromoly steel and cold-forged to ensure molecular integrity

These 7/16 in

They will fit 8

Oldsmobile 400 425 455 MID-AIR™ MidRise Aluminum Intake Manifold [Black] Due to the large-diameter 13The Speedmaster MID AIR design features the identical plenum and runner design as the normal mid rise. The main difference is that there is an open area under the plenum chamber. This feature is sometimes called an air gap design. The air flowing under the plenum provides a cooler charge for the incoming air with less heat transfer from the engine. This cooler air charge provides additional power and torque.