Steam relief

I got together with my old engine builder some time ago and he mentioned the tendency of Chevy big blocks to have steam pockets in the cooling circuits around #7 and #8 cylinders. On many of his race engines (IMSA Corvettes, Air Race Airplane, and offshore engines) he plumbed relief lines from the back of the intake manifold forward to the thermostat housing. I've been contemplating running pressure relief valves (2 per motor) into high pressure hoses and dumping the steam overboard or may back into the thermostat housing. One "off the shelf" solution is the bronze water heater safety relief valves. I would like you to critique this concept. Thanks.

I believe this is a must do on all BBC after my exhaust valves collided with my pistons on 3 different occasions.
When I switched out my heads from GM's to Merlin's I wiped out valves within 2-3 mins once on plane. (I also eliminated my water pump for a crossover)
I would just dump the water and not run a pressure relief. You want flow for cooling. I have been running this way for 3yrs with no problem.
I also run on Lake MI in 50*F water in the middle of October/November with no issues and can maintain 130*F water temps at idle and 160*F running.
Here is my thread chronicling my ordeal.

Another valve meets a piston - Boatfreaks

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Originally Posted by Rookie

I believe this is a must do on all BBC after my exhaust valves collided with my pistons on 3 different occasions.
When I switched out my heads from GM's to Merlin's I wiped out valves within 2-3 mins once on plane. (I also eliminated my water pump for a crossover)
I would just dump the water and not run a pressure relief. You want flow for cooling. I have been running this way for 3yrs with no problem.
I also run on Lake MI in 50*F water in the middle of October/November with no issues and can maintain 130*F water temps at idle and 160*F running.
Here is my thread chronicling my ordeal.

Another valve meets a piston - Boatfreaks

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Thanks Jason and more pix of your setup would be very appreciated, Jeff

Not a problem next time I'm out to the shop I will get them.
Basically I just drilled out the back corner of my intake like your builder suggests. Then I ran a 3/8"NPT brass barb to 3/8" hose to the water
ports on my exhaust manifolds. You could just Tee into your water hoses that feed your exhaust manifolds from your thermostat housing.

I get it in concept, I'm visual and a picture is worth, well you know........:)

Was that problem only on the Gen IV ?

Not sure Paul, but my engine guy says that #7 and #8 are know steam generators and apparently some time the problem is wrong head gaskets (maybe a Mark IV/ Mark V issue). However, my guru Pat says that much of it is poor design and that his company did this "fix" as a matter of course. We will see.

Somewhere in there was an issue with head gaskets blocking the passages in the front on one style block to the later style head, or something like that. If the gasket with the water passages open in the front was used the rear would overheat every time.

Indeed, there is an issue like that out there,

I can find nothing on it being an issue in any other application.

One thought is that with crossovers, the flow isn't as good as can be. In any event the intake manifolds are over at a friends place that has a milling machine getting the rib milled down and then drilled and tapped for #6 AN fittings which will be plumbed back to the thermostat housings.

Did your engine mention this at all? I think this was the main issue with bigblocks.

Series-cooled block, parallel-cooling head gasket?

Many parallel-cooling head gaskets have the big hole in the back blocked, greatly restricting coolant flow at the back of the head.

If the block is a series-cooled unit, there's no coolant flow up to the head between the cylinders.

End result is terrible coolant flow, overheating, and harsh language because NOTHING will help the overheating. It will not respond to different fans, different radiators, different timing or carb adjustments. No water pump on Earth, and no thermostat changes will help.

Easy fix: Replace head gasket with series-flow unit, or remove heads, drill three holes in each block deck surface using the parallel-flow head gasket as a template. One hole in the block may exist, but need to be ground oblong to match the head gasket.

He was mentioning the BBC series/parallel block head problem. He also mentioned the asymmetrical design of BBC heads.Thanks for the extra info Paul, I'm going to pass it on to him. He's a pretty bright guy that has given talks (I think) at SAE conventions regarding the thermodynamics of IC engine cooling.