Fits as a direct replacement for the standard 55mm manifold. It is a better; stronger and a more heat resistant replacement for the stock plastic (polymer) manifold. T6 heat treated cast aluminum that is CNC machined on the outside for perfect fitment and capable of a higher flow; which adds 3 to 5 horsepower. Especially above 124" the stock manifold becomes a restrictive part. Comes with a rubber o-ring seal. Easy to install; re-using all stock parts. OEM replacement reference 27300121. Note: For replacement o-ring seal see 974061.