350 Chev head gasket water holes too small? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 04-10-2007, 06:59 PM
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350 Chev head gasket water holes too small?

I'm replacing the head gaskets on the 350ci chev motor because one blew out and filled #6 with water when cold. I noticed the old and new gaskets both have very small upper water passage holes (1/8") but both the block and heads have much larger passages. This was particuarly alarming since the gaskets were balloned in at the restricted water holes as though water couldn't get through well enough.

Why are the gasket water holes so small? Can or should I drill the gaskets to match the block and head water passages or maybe even just a little bigger than they are? What are the possible pros and cons of such a mod to the head gaskets?

Thanks guys.

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Old 04-10-2007, 07:16 PM
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If you enlarge the holes you will destroy many years of research by the GM cooling guys. LEAVE THEM ALONE. Or you will create an overheating monster..
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Old 04-12-2007, 07:10 PM
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Huh?

I appreciate the response. I'm not sure I buy that though. If we were to believe that the engineers at chevy designed everything to the utmost of it's performance then we would never have to modify anything. We all know that's not true. I honestly just think about things too much and don't mean any disrespect by my thoughts. I just like to know the how and why behind the things we do and how my engine works.

What would cause the overheating if the passages were enlarged? It would seem that opening up the holes would allow better circulation. That in turn suggests to me a cooler running head. Maybe too cool. Maybe that's the reason or maybe not. Is it to allow air out when the water runs? Does water ever go through the upper portions of the head? I don't know, but I'd like to.

Thanks again.
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Old 04-12-2007, 07:25 PM
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The smaller holes force the water to circulate around and to the ends of the block. Like little geysers. If you open them up. The cooland will just lay undisturbed in the bottom or ends and not move the absorbed heat out of the block.

I have already had a customer open the holes up on a Big block chevy. Trying to improve the cooling in a suburban. The motor overheated in about twenty minutes and would not cool. A lot of my shops time was wasted trying to find the problem. As we had done the machine work (not the assembly).

Customer was not happy with the billing, after it was found that he caused the problem.. So don't screw around with something that has been proven reliable since 1955..
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Old 04-12-2007, 07:31 PM
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Quote:
Originally Posted by rlmfire
I appreciate the response. I'm not sure I buy that though. If we were to believe that the engineers at chevy designed everything to the utmost of it's performance then we would never have to modify anything. We all know that's not true. I honestly just think about things too much and don't mean any disrespect by my thoughts. I just like to know the how and why behind the things we do and how my engine works.

What would cause the overheating if the passages were enlarged? It would seem that opening up the holes would allow better circulation. That in turn suggests to me a cooler running head. Maybe too cool. Maybe that's the reason or maybe not. Is it to allow air out when the water runs? Does water ever go through the upper portions of the head? I don't know, but I'd like to.

Thanks again.
first understand how a cooling system works, then you'll understand Chevy got it right. not only does it allow flow, rather than just pooling, as stated above it allows it to absorb more heat. Thermostat operates on the same theory, slow the water down ( more like stop with the thermostat ) and allow it to absorb heat, water that flows too fast, absorbs less heat, and does not cool as well.
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Old 04-12-2007, 07:54 PM
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Hey pal, ask a question respect the answer. I understand people having to
learn, And yes personally that the dumbest question I ever heard was asked
I didn't say so. But when someone gives you an answer, set back a couple
days and read the mail. If someone's reply on this site is totally out in left
field, there usually will be some discussions and from that you will learn. But
smart cracks will not get you respect.
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Old 04-12-2007, 08:05 PM
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The holes in the head gasket are the size they should be. If they are opened up water wouldn't flow to the back of the engine. It would come out of the pump and go right up the first set of holes in the head on both sides and through the thermostat and back to the radiator. The back of the block and heads would get no cooling.

The holes in the block and heads are huge so they could get the casting sand out when they poured the block. Yep, it's that simple...

As far as the slow water cools better I disagree.

This is from folks who do nothing but make water pumps for engines that cost more than most people make in a year..Stewart components

"A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called "hot spots", which can lead to failures."

You can read the whole thing here: http://www.stewartcomponents.com/tec...ech_Tips_3.htm

Engines don't overheat everywhere at once. they start to boil away coolant in hot areas first. On a SBC between the center two cylinders where the exhaust ports are next to each other is usually the first place. Once the coolant boils away in a small area the gases form a pocket that keep coolant from contact with the metal making it hotter, boiling away more coolant making a bigger gas pocket and on and on.
Thats why on engines that run hard for long periods it's common to route cooling directly to the head at this point and sometimes straight to the back of the block.
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Old 04-14-2007, 08:11 PM
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Ah ha!

Thanks guys.

Bobcrman and SlowGTA thanks a lot. Now I get it. Makes sense now. I appreciate the explanations. Bob, hope you weren't offended. Seems a couple of guys think I stepped on your toes. I try to come off as harmless as I can. Emails can be a hard thing to interpret people's real feelings and emotions. I'm very happy with the explanations and replies.

I'm off to finish my rebuild. Thanks again!
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