i'm changing my head gaskets cuz i blew em (yay)

when i took off my intake manifold the rear water passage was blocked off by the old gasket,

i know i was getting water out of the intake manifold through a pipe in the rear

when i put the new gasket on should i leave that passage blocked or would i better off opening up that passage

what effect does it have on cooling?
i dont want to overheat again because there isnt always a spot to pull over on the highway

 

From the factory the gaskets have a metal insert that restricts coolant flow through the intake. It does not block it off. There should be a small hole in the center of the insert. I am not sure why it is there, probly something to do with emissions, but I the new gaskets should come with these. I would install them with the new gaskets.

 

thanks
yea the new gasket is blocked off with a little hole in the top
anyone know why?

 

You dont need water in the back of the intake manifold as there is nothing up there that needs to be cooled. It's got a hole just in case there really is a cavity in the intake manifold that is full of air. If there was no hole, you would have 15 PSI of water pressure pushing on that steel block-off plate, and eventually it would fail. By placing the small hole you get pressure equalization on the blockoff plate, yet you retain the ability to shuttle coolant forward, across the cylinder head combustion chambers with maximum flow to carry heat forward towards the thermostat and out to the radiator. Without the blockoff plate you get hot coolant that stagnates around the back of the cylinder head and intake manifold. I surmise that this might help cause detonation problems on cylinders 7 and 8 on engines that are close to the edge of timing and heating.

FWIW, Many aftermarket intakes do not even have ports cast into the rear. However all cylinder heads have the ports in order to make the head interchangeable as either a left or right cylinder head.

 

that makes alot of sense
thanks

 

Not sure which year/engine we're talking about but many 3rd gen engines have the outlet pipe to the heater hose attached at the BACK/PASS. SIDE of the engine. If your engine has it back there then coolant must flow to that hose fitting at the back for you to have heat!

On most SBC engines there is no coolant passage back there and the intake manifold blocks it off completely, whether you put a restrictor plate in there or not.

The ONLY reason that there are even coolant passages in the backs of the heads is because SMALL BLOCK CHEVY CYLINDER HEADS ARE INTERCHANGABLE SIDE-TO-SIDE ON THE ENGINE. There is no "left" head or "right" head. Think about it. That's why the heads must have mirror-image coolant passages on both their front and back ends. Move it from the right bank to the left bank and the "rear" collant passage becomes the "front" coolant passage. Get it?

 

That's what I thought I said, but in less words:

Nice info on the heater port though. I've not run across one of those intakes yet. I'll keep my eyes peeled.

 

Have a look at any 305 TBI engine in a Camaro or Firebird and you'll see that rear heater hose fitting.

 

mine is an 87 iroc with a carb'd 305
stock motor
it does have a fitting in the rear water passage that connect to the heater hose through a funny tee

 

Bingo, that's what I'm talking about.

 

how can i get rid of that. it looks epoxied on or something, but from underneath it looks like it just threads on and i could replace it with a plug

i want to get rid of it because i can't find a tee that wont leak