This is the only 3 into 1 manifold adapted for road use. It has clamps for sealing the downpipes. The pipes have been sized to be very useful on certain 1275-1400 engines where mid-range torque and fuel economy are paramount. The collector piece outlet end is 1.875" outside and 1.75" internal diameter. The 3 into 1 design should be used with camshafts of at least 286 degree duration, but best with at least 296 degrees!