okay i know i said the F-word but i need some help trying to figure this issue out . well it's my neighbors 66 ford econoline van with a 240 inline 6 cyl and we just got done putting a 4bbl intake and header on it .the intake is a offenhauser dual port 360 4 bbl manifold and it has a port /passage on the underneath side of the manifold . i think this is for exhaust heat to warm the intake manifold like our chevy's have .

since we're running hooker headers on it there no provision for adapting to the intake to heat it . so is there any issue,vacum leak or any other problem by leaving this passage open .

Man, if you weren't a moderator you'd be locked out for sure on this one! ;)

To answer your question from general knowlege, no, there won't be any vacuum leak. Those heat passages have to be totally sealed off from the intake passages or you'd be sucking exhaust gasses (EGR) constandly, obviously causing all sorts of drivability problems if it would run at all. If it had an EGR system built into it a leak might be possible, but I doubt that's a problem with that intake since I don't think it has EGR provisions anyway.

He can run a stovepipe from a close header tube to it if he wants to keep it half-way functioning for cold weather..

pdq67