Okay guys what's with the 7th bolt hole on the exhaust side of the head? and what year did chevy put it there? A friend has a 84 blazer with a burnt valve, and can't afford a valve job right now so I donated a pair of 75 400 heads the 400 heads lack the last bolt hole, is this going to be a issue? the motor in it right now is a goodwrench motor thanks!

I think they are just a universal design by GM. Some cars had manifolds that used the front bolt, some the rear, depending on how the accessories for that particular mounted.

Those heads (with the 7th hole) are specific to trucks from what I've found. Dealt with that crap on my 84 'burb. Put a 74 motor in there and the stock manifolds didn't fit right http://www.nastyz28.com/ubb/frown.gif

That 7th hole is the '6th' (last one) on the stock manifolds....so if it isn't on, you might not get the proper seal.

that stupid 7th bolt was also used on 85 ta's with a ho 305 i know this because i tried putting the manifolds on my 1980 caprice drivers side fits but the passenger side uses the last bolt hole.

I'm going over next week to look at the blazer again, I just don't remember if there were any brackets bolted to it, If not he may have to live with a exhaust leak. at least the car will run.

The 7th hole was something Chevy came up with later in the game. I have seen it on 305s, but not on 350s and 400s, although I bet some of the later 350s have it too. Some head castings have it and others don't. You shouldn't need it for most applications. It would be a problem only if some of your accessories need it to mount there.