HI-RAM Series: Manifolds are used primarily in drag racing, tractor / truck pulls and performance marine applications where high rpm is required. The effective rpm range will be between 2,500 to 10,000 rpm, depending on specific model and application. The WEIAND Hi-Ram, with its patented D-shaped port runners and large plenum chamber, provides optimum thrust of the air / fuel mixture to the cylinder head intake ports. For maximum performance in a normally aspirated competition application, the WEIAND Hi-Ram Series is the manifold of choice!