Originally Posted by OneMoreTime
would certainly solve an issue for me as I have a 250 chev 6 head to 12 port and filling the gaps on the 6 port head had me puzzled..
I did exactly that on my 230 inline 6 head! I cast up '180 deg', isolated runner aluminum 4-bbl manifold and used Devcon plastic steel to isolate the siameze ports in the head. I built dams on one side using modelling clay, cut a mesh of window screen as internal support inside the plastic and poured the plastic steel and let it set up. A little grinding w/ a burr blended the ports to perfection. I brazed a rod to the bolt bosses inside the runners to complete the isolation. I used a Holey 390cfm 4-bbl carb. Made equal length 34" primary dual headers. This combo was great, car would climb a rope w/ bottom end torque, great gas mileage, plenty of top end too. See photos of the project in my Journal