Power Driven Diesel 3.9 Cummins Stage 1 CNC Ported 8-Valve Cylinder Head | 1989-1998 Cummins 4BT 3.9L

New manufactured aftermarket 8v Cummins ported stage 1 cylinder head with reinforced ribs throughout, strengthened walls, thicker spring seats and deck surface. The gasket surface is freshly machined. This stage 1 ported head features a modern CNC port job that creates balanced flow across all 4 cylinders while providing large flow gains with the stock sized valves. On our flow bench test, we saw an average flow of 137% on the intake and 134% on the exhaust with peak valve lift numbers showing a 48% increase on the intake and a 46% increase on the exhaust. Our test recorded a maximum intake flow of 146 CFM and 152. CFM exhaust flow at 28″. Keep in mind that flow benches vary so it’s likely that some test stands will show slightly more and some will show slightly less flow.

In real-world testing, the higher flow from this ported head slightly raised engine efficiency and peak power performance with resulting lower boost pressure and lower EGT readings compared to the stock cylinder head. Although a bigger than stock camshaft is not required, these ported cylinder heads really shine when combined with an aftermarket camshaft with larger than stock duration and lift!