hey all, i took my intake manifold off today for the first time and i discoverd that the back waterjacket is not in use (blanked off) wouldent this cause it to run hot in the rear of the heads? I think it is the OEM manifold all it has on it is "GM CFM".

It's perfectly normal.

Thats normal. No factory manifold ever had a passage back there.

The reason there are water jacets at the back of the heads, is that there are not 2 castings of a set of heads... its only one casting, one facing one way, and the other reversed. What I mean is, the front water jacket on one head, is the back one on the other head.

AH i c but if i drilled a .78in/20mm hole in either side of the manifold and put a fitting in both holes with hose going from one side to the other would the car run cooler?
I know not a lot but a little?

Not enough to be worth the effort, if at all.

thanks for the reply, i wont worry about doing it then.

Yeah there's probably over 100 million SBCs that have been on the road now for over 50 years; and it didn't matter to them.

I'm guessing your's'll probably be OK without it too.

Although, in the latest few years (from around 87 or so on up), they DID use those extra passages to feed the heater core. Probably saved money on all that extra heater hose they didn't have to put on new cars. Which, I laugh; but at, say, $1 per car over a few million cars, that might add up almost to some pocket change.

Knowing GM it probably cost them $1.50 in machining to save that $1 of hose.