Benefits of 4-port water bypass on a SBC?

[fabr]

Here's a little nugget for thought from Stewarts site and falls in line with I have always thought. The old wives tale about coolant flowing too fast causes overheating since it isn't in the engine long enough to absorb heat kind of goes POOF!

"Higher coolant flow will ALWAYS result in higher heat transfer. Coolant cannot absorb heat after it reaches it's pressure corrected vapor point. Furthermore, coolant absorbs heat at a progressively slower rate as it approaches this point."

The basic rule of heat flow is that the larger the temperature difference ,the faster heat flows toward the cooler surface is indisputable.

[NewbVetteGuy]

Here's a little nugget for thought from Stewarts site and falls in line with I have always thought. The old wives tale about coolant flowing too fast causes overheating since it isn't in the engine long enough to absorb heat kind of goes POOF!

"Higher coolant flow will ALWAYS result in higher heat transfer. Coolant cannot absorb heat after it reaches it's pressure corrected vapor point. Furthermore, coolant absorbs heat at a progressively slower rate as it approaches this point."

The basic rule of heat flow is that the larger the temperature difference ,the faster heat flows toward the cooler surface is indisputable.

I don't think it can be said too much. (More coolant flow = more better(er) as the general rule.)

But if you're INCREASING flow, you're DECREASING pressure and the localized boiling point. When running 100% water that seems like it could be an issue, eventually. (HMM.. But faster flow means a lower max / engine outlet temperature so it theoretically keeps the coolant further away from the boiling point, so heck if I know whether the net impact puts you closer to boiling or further from it; a wild-ass guess is slightly closer...)

In Stewarts's "Advanced Cooling Basics", they include a table that shows the typical cooling system pressures at various points of the system with a coolant flow of 100 GPM (I'm assuming with their Stage 4 pump):

Following is a typical Winston Cup engine at 100 GPM:

Lower radiator hose = 1.5 PSI
Block and cylinder head - each (at 50 GPM) = 8.5
Outlet manifolding = 1.25
Top radiator hose = 2.25
Radiator = 1.5
Total = 15.00 PSI

--It kinda shows what you'd expect, but it's cool to see it. Overwhelmingly the huge restriction / point of highest pressure is at the cylinder head, but that's probably a good thing.

I'm not sure whether this number is taken with the extra coolant hoses in place or not, but it WOULD be interesting to see those numbers on an SBC with and without the extra rear to front and/or between-the-center-exhaust-ports coolant bypass hoses. (I have to think that adding AN hoses increases flow and decreases pressure there.)

I also think the top radiator hose being the #2 restriction / highest pressure point, is by-design to keep up the pressure there and in the block -so many engines from the OEM reduce the diameter going into the radiator there and I've read increase the diameter going into the outlet to try and prevent too large a pressure drop at the pump inlet to reduce the risk of cavitation due to a big pressure drop there.

https://www.stewartcomponents.com/index ... tion_id=14


Adam

[Geoff2]

I don't see how increasing flow will decrease pressure. The opposite will occur.

The restrictions in the engine are the coolant passages where they cross over from block to head via the head gasket. Either the hole in the block, the head or the gasket will be the smallest area & this regulates the flow through that particular orifice. If you add up the area of all these orifices, they are considerably greater in total area than the thermostat opening; so the stat opening becomes the restriction to flow; that is why a washer or similar is recommended if the stat is removed. To regulate flow/pressure. So the pressure will build up behind this restriction & attempt to reduce/eliminate nucleate boiling.

[Tom68]

I don't see how increasing flow will decrease pressure. The opposite will occur.

The restrictions in the engine are the coolant passages where they cross over from block to head via the head gasket. Either the hole in the block, the head or the gasket will be the smallest area & this regulates the flow through that particular orifice. If you add up the area of all these orifices, they are considerably greater in total area than the thermostat opening; so the stat opening becomes the restriction to flow; that is why a washer or similar is recommended if the stat is removed. To regulate flow/pressure. So the pressure will build up behind this restriction & attempt to reduce/eliminate nucleate boiling.

That's why restrictors go in place of thermostats and why there's no need for high flow thermostats I guess.

[NewbVetteGuy]

I don't see how increasing flow will decrease pressure. The opposite will occur.

The restrictions in the engine are the coolant passages where they cross over from block to head via the head gasket. Either the hole in the block, the head or the gasket will be the smallest area & this regulates the flow through that particular orifice. If you add up the area of all these orifices, they are considerably greater in total area than the thermostat opening; so the stat opening becomes the restriction to flow; that is why a washer or similar is recommended if the stat is removed. To regulate flow/pressure. So the pressure will build up behind this restriction & attempt to reduce/eliminate nucleate boiling.

That's why restrictors go in place of thermostats and why there's no need for high flow thermostats I guess.

Crud... I missed these two replies back in July...

If there's no need for high flow thermostats then why do the high flow water pump companies recommend or MANDATE them on their higher end water pumps? (Stewart recommends them for even their Stage 1 pumps and says they're "required" for stage 2 and up...)


Adam

[NewbVetteGuy]

I don't see how increasing flow will decrease pressure. The opposite will occur.

The restrictions in the engine are the coolant passages where they cross over from block to head via the head gasket. Either the hole in the block, the head or the gasket will be the smallest area & this regulates the flow through that particular orifice. If you add up the area of all these orifices, they are considerably greater in total area than the thermostat opening; so the stat opening becomes the restriction to flow; that is why a washer or similar is recommended if the stat is removed. To regulate flow/pressure. So the pressure will build up behind this restriction & attempt to reduce/eliminate nucleate boiling.

You might be right; I'm not sure.

I was mostly thinking of airflow and everywhere that air increases in VELOCITY, it decreases in pressure and vice-versa and thinking "hey moving air and moving liquid should follow the same principles"... And then applying it to moving coolant in the cooling system and areas of higher velocity vs. pressure.

-Still seems right to me. Opening up the inlet to the water pump to a larger volume at the water pump side of the hose would slow down the flow and increase pressure to help reduce the risk of cavitation at pump inlets.

The lack of compressibility of water and air's ability to be compressed sneaks up and gets me sometimes, though...


Adam

[Tom68]

I don't see how increasing flow will decrease pressure. The opposite will occur.

The restrictions in the engine are the coolant passages where they cross over from block to head via the head gasket. Either the hole in the block, the head or the gasket will be the smallest area & this regulates the flow through that particular orifice. If you add up the area of all these orifices, they are considerably greater in total area than the thermostat opening; so the stat opening becomes the restriction to flow; that is why a washer or similar is recommended if the stat is removed. To regulate flow/pressure. So the pressure will build up behind this restriction & attempt to reduce/eliminate nucleate boiling.

That's why restrictors go in place of thermostats and why there's no need for high flow thermostats I guess.

Crud... I missed these two replies back in July...

If there's no need for high flow thermostats then why do the high flow water pump companies recommend or MANDATE them on their higher end water pumps? (Stewart recommends them for even their Stage 1 pumps and says they're "required" for stage 2 and up...)


Adam

Stewart has some great info on cooling systems.

Small block Chevs have an inadequate bypass system that a lot of people block as well. So whilst your thermostat is closed there is no flow, therefore the pump works with no flow, let alone with a restrictor instead of a thermostat that a lot of racers run.

Might be better to adapt a proper bypass thermostat like a Cleveland or an LS.

[Rick!]

Heat exchanger calorimetric curves knee out in two ways:
First is that there is only so much internal surface area to conduct heat from coolant flow to be convected to the atmosphere, hence, after some BTU value, more coolant flow does not produce significant more heat rejection.
Second, holding coolant flow constant, there is a similar point in the heat exchanger's calorimetric curve where increasing the air speed across it doesn't appreciably increase heat rejection.
Both of the above will respond to a properly sized heat exchanger for the intended use. You can cool a superbike with two radiators that barely add up to a normal sized heater core if you always keep it above 100mph. But they perform poorly in highway traffic at 90F. It's all in what is needed for the intended duty cycle.

The one environment where ever increasing coolant flow always increases heat transfer is a boat with a water cooled engine with no stat. The body of water is an infinite supply of constant temp coolant and the faster the water flows through the engine, the more heat it will scrub out. My Vrod has a 145F stat so it'll make 400hp every time I ask for it, my former 210hp SBC without a stat didn't really care. YMMV.

[NewbVetteGuy]

That's why restrictors go in place of thermostats and why there's no need for high flow thermostats I guess.

Crud... I missed these two replies back in July...

If there's no need for high flow thermostats then why do the high flow water pump companies recommend or MANDATE them on their higher end water pumps? (Stewart recommends them for even their Stage 1 pumps and says they're "required" for stage 2 and up...)


Adam

Stewart has some great info on cooling systems.

Small block Chevs have an inadequate bypass system that a lot of people block as well. So whilst your thermostat is closed there is no flow, therefore the pump works with no flow, let alone with a restrictor instead of a thermostat that a lot of racers run.

Might be better to adapt a proper bypass thermostat like a Cleveland or an LS.

A street car with a heater core has a built-in bypass.
The EMP /Stewart / Robert Shaw 301 SBC high flow thermostat comes with 3 3/16" bypass holes to keep fluid moving before the engine's fully warmed up and then is high flow when you need the cooling. Would take a little bit longer to warm up vs. no bypass, but it's a dead-simple bypass that also gets rid of air and should reduce bore wear with high expansion pistons while they're cold. Seems like almost all "win" to me.

https://www.stewartcomponents.com/index ... ry&path=61

From the Stewart page above: "Manufactured by Robert Shaw and modified by Stewart, these custom thermostats feature a balanced sleeve design and are constructed for high flow, high RPM applications. Strongly recommended for any performance application - must be used with Stewart Stage 2, 3 or 4 water pumps."


Right now I'm sticking with more flow is better up until until coolant mixture starts boiling in the heads. At that point I'd ideally like a thermostat of the same temp rating, but with slightly less flow to up the pressure. (I realize you don't get to choose the flow with a thermostat like you do with a restrictor, though.) -I could also just increase the amount of anti-freeze in my mixture at that point.