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For reference, here are two different sbc head gaskets, Fel-pro and Cometic. Absolutely no difference in coolant regulation front to rear….

View attachment 304095

View attachment 304096
Note the center water passage between where the exhaust valves are. It's big while the ones on the other 2 are small. On older small blocks the center passage in the block is small and needs to be enlarged. Can't remember for sure but I think it's 1/2inch.
 

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MACH Development developed these steam tubes for Pro Stock using the (Pontiac?) heads that were poorly designed and they were promoting steam pockets. These tubes fixed the problem and eventually the problem was resolved with revised cylinder head castings.
Have any of you been on a dyno session and heard steam pockets? I have and it was one of my 390 D/S engines. Bud Yancer shut it down immediately because he knew the damage that it could cause. This was a filled block and filled blocks can have these problems; I was using factory water pump at the time and he had me get a 35 GPM Mezeire water pump and problem solved. We also ran external coolant lines; one in each rear corner connecting to a Y fitting to the thermostat housing. Eventually stopped that and still retained a primitive air bleeder which I still use. Air needs to be bled from the highest point of the engine water flow and if you have to, create a high point (typically a heater hose port).
Take a look at these steam tubes:
 
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My concern has always been the water in the by-pass hoses is not going through the cylinder heads and provides no cooling. I do run -4 hoses to remove any steam that might form.
I don't know if there is any "one answer fits all" for this issue. If it works for you.... do it.
 

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This modification has been around forever. What it does is helps promote more water flow at the rear of the engine block and head. I have seen A-B testing and never saw more then 5-10 degree drop in the back of the head and didn’t see any temp reduction in the water coming out of the water neck. This was 20+ years ago so I don’t remember the exact numbers and I’m pretty sure it was on a Pontiac engine in a daily driver. In my opinion it doesn’t help in a drag race only application using an electric water pump. In a road car or endurance application it can help but you need to use at least a -6 hose to move enough coolant.

What we do on our Bonneville motor is we plumb high pressure coolant from the pumps outlets to these ports, and also to the middle of the head. And again don’t have the exact numbers but we went from only going a couple miles to being able to go the full 5 miles if we want.
 

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My concern has always been the water in the by-pass hoses is not going through the cylinder heads and provides no cooling. I do run -4 hoses to remove any steam that might form.
I don't know if there is any "one answer fits all" for this issue. If it works for you.... do it.
But as the general rule the water makes it way back to the rear cylinders and then flows through the heads all the way to the front. It's a very long path to get to the radiator, gathering more heat all the time. If the rear cylinders really are warmer with the stock coolant flow setup, then don't the rear-to-front coolant bypass hoses slightly alter the stock flow providing additional cooling "bias" towards the rear? -If you're pulling more coolant out of the top rear by making it's flow path back to the radiator easier, you get more coolant pulled towards those hot rear cylinders, evening out the temps, no?

(That's what I'd expect to see happen; not that I have any CFD sim to back it up...)


In a similar vein of thought, my thinking is that the stock early Gen1 coolant bypass actually makes cooling the rear cylinders slightly worse- if the bypass flow is going straight up to the front of the passenger side head, isn't it just going to quickly flow out of the head and into the intake's front ports and then out a bypass hose, through holes in the thermostat or out the thermostat when it's open, essentially stealing away coolant flow from the rear cylinders that actually need it more?

(A "bypass" should increase the flow where it's actually needed, right? -My current thinking is that the stock bypass does the opposite of that and the rear to front bypasses, do exactly that.)

If Peter is overheating at cylinders 8 & 7, you don't steal from Peter to pay Paul who's already nice and cool in cylinders 2 & 1, you steal flow from Paul and give it to Peter, by blocking off the stock bypass and adding the rear to front crossovers (or making the block to head coolant holes in the head gasket smaller in the front and larger in the rear...) No?




Adam
 

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For reference, here are two different sbc head gaskets, Fel-pro and Cometic. Absolutely no difference in coolant regulation front to rear….
Scott, there are LOADS of differences in those gaskets, including front-to-rear...

The Cometic has the early SBC water pump bypass hole highlighted in thick red blocked off, while the Felpro has it open. The Felpro 1003 has the hole right next to it opened up larger than in the Cometic -both of these features would push more coolant towards the back of the block rather than from the front of the block and up to the head and then out the front of the head back to the thermostat exit.

The Felpro has a bunch of extra coolant holes right around the troublesome siamesed exhaust ports, which, I like, though.

The Felpro looks to have better center exhaust port cooling, but the Cometic pushes more coolant to the rear as far as I can guestimate...

Regardless of what the differences in flow accomplish, they are definitely different towards the front of the block.
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@ChopperScott Do you have the Cometic Gasket #? I'd love to look at it in more detail.

Adam
 

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I can understand using small (-3 or -4) to vent the system. Any significant flow is going to rob flow from the cylinder heads.
Is it going to "rob flow" from the cylinder heads, or just alter the path of the front so that it's more towards the rear? The flow is still exiting the rear cylinders of the heads. -You're just robbing flow from the front and giving more of it to the rear; given that the rear cylinders are the hottest, that actually makes sense if your goal is more even heat distribution, no?

Adam
 

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Discussion Starter · #51 ·
This modification has been around forever. What it does is helps promote more water flow at the rear of the engine block and head. I have seen A-B testing and never saw more then 5-10 degree drop in the back of the head and didn’t see any temp reduction in the water coming out of the water neck. This was 20+ years ago so I don’t remember the exact numbers and I’m pretty sure it was on a Pontiac engine in a daily driver. In my opinion it doesn’t help in a drag race only application using an electric water pump. In a road car or endurance application it can help but you need to use at least a -6 hose to move enough coolant.
It makes sense not seeing a temp drop at the water neck. The same amount of heat being transferred, but more equalized between cylinders.

There is a competition in drag racing where it may benefit... True Street. I've run in a class where we all have to drive our street legal drag cars on a 30 mile road trip, then make three hot laps down the track without shutting down.
 

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Discussion Starter · #52 ·
Scott, there are LOADS of differences in those gaskets, including front-to-rear...

The Cometic has the early SBC water pump bypass hole highlighted in thick red blocked off, while the Felpro has it open. The Felpro 1003 has the hole right next to it opened up larger than in the Cometic -both of these features would push more coolant towards the back of the block rather than from the front of the block and up to the head and then out the front of the head back to the thermostat exit.

The Felpro has a bunch of extra coolant holes right around the troublesome siamesed exhaust ports, which, I like, though.

The Felpro looks to have better center exhaust port cooling, but the Cometic pushes more coolant to the rear as far as I can guestimate...

Regardless of what the differences in flow accomplish, they are definitely different towards the front of the block.


@ChopperScott Do you have the Cometic Gasket #? I'd love to look at it in more detail.

Adam
The head gasket holes are symmetrical front to rear, if you fold the gasket or flip it over.

That particular Cometic gasket I posted is part # is 5399-040.
 

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I guess I'm dumber than a stump, I always thought the sprint cars guys started doing that to bypass some of the cooling fluid to the heads so the heads would run "hotter" when using alcohol, :confused:.
 

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Hmmm, modern roundy round guys don’t seem to need all them extra hoses. There are bleeds in the rear though. Still waiting for real data on ET consistency within .003 due to extra coolant hoses. Anecdotes don’t count. Carry on.
 

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Thats because R07 engine is not an gen1 sbc...
And all the cooling system tricks and routing we applied over the years to the standard sbc are built into the architecture!
 

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Hmmm, modern roundy round guys don’t seem to need all them extra hoses. There are bleeds in the rear though. Still waiting for real data on ET consistency within .003 due to extra coolant hoses. Anecdotes don’t count. Carry on.
Bleeds in the rear?!?
 
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