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Interesting stuff. A restrictor at the head outlet would provide a small increase in the pressure in the block and head, but you can get a much larger pressure increase by simply going to a higher pressure cap--for industrial situations where pump cavitation is a problem, pressurizing the system is the fix. In 'merican units, the heat transfer equation boils down to BTU/hr=500*GPM*dT. In practice, as the flow rate increases the temperature deltas will decrease, but the net heat transfer will increase. More turbulent flow is part of it. All of this suggests that measuring the temperature of the coolant is a lousy way to monitor the effectiveness of the cooling system. IMO, we should be measuring the metal temperature of the cylinder head.
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A higher pressure cap would only work if the actual pressure of the system exceeded the pressure of the lower pressure cap. If you have adequate header tank volume, you tend to be able to run lower pressure caps. I actually (somewhat inadvertently) ran a no-pressure cap system quite happily for quite some time on a street car. The cap didn't seal to the rad. the car had tons of header tank volume, never overheated, never lost coolant. Just goes to show there is more going on inside of these things than sometimes meets the eye...
I'm now getting interested in the whole header tank idea. A lot of newer race cars have about zero header space and no swirl pot. Older cars had maybe a half quart space at the top of the swirl pot. My street car has easily a half gallon of header tank, and a lot more when I forget to keep it topped up. I bet you could stabilize the cooling system a lot better if you added header tanks to cars that had problems.
Brian
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The main object of a higher pressure cap is to prevent or reduce coolant boiling, localized or otherwise. While having more overflow tank capacity may keep you from losing water, it does not fix the basic problem of coolant boiling. More pressure does.
This side discussion was about water flow speed/restrictors, and their ramifications, so I did not mention the pressure cap. Also the original poster did not mention coolant loss, so I didn't think the system pressure was his problem.
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Head Gasket
Whenyou replace the head gasket, are you useing a Mono Toque type? I now will pull down these on a race motor after a heat cycle, and use water wetter, this will help more with heat transfer than most other things, provided your radiators are clean, block is clean, and you do not need a restrctor in place of the thermostat, which you throw out as well, don't need it, with thse engines (and 1600 XF) you need to heat sink them before any race, so heat is even and oil is up to temp, and water temp is ok.
Roger
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Sorry Roger, mono toque? Us Canadians have WAY more than just one toque.
We were discussing that this car has been through 2 guys since the engine rebuild, and may have not had the head re-torqued after a little while. Is this the typical procedure? How long before the re-torque?
Gary
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Well, we got the head off, and found an issue with the head gasket.
It's close to getting buttoned back up, and should be running after another couple hours. We'll see if it fixes our issue, I'm rather confident it will.
Gary
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you forgot to pluralize one word Gary:p
Gord
