Chris and Mark,
I have a couple of comments regarding your cooling system thinking. 1. Chris you said that the radiator inlet and outlet will both be on the bottom of the radiator, so I am assuming that you are running a double pass radiator and that you will have vent valves on the tops of both tanks to make sure that the radiator is actually full of water before you run? I will also assume that the design of the radiator, if it is double pass, is such that the design will flow the cooling water at a sufficient velocity to insure turbulent flow and not at a large increase in back pressure due to the increase flow velocity. This is very important with electric water pumps as they do not produce much pressure without an accompanying reduction in actual flow. The largest Davis Craig electric pump EWP 150 looses 50% of its flow rating at 5 psi of back pressure! (Note that Davis Craig are the only electric water pump people that actually give you flow vs back pressure graphs.) So any additional flow restrictions can counter the supposed cooling efficiency gain of doing a double pass radiator. 2. Mark, you are proposing to machine a special venturi shaped water out let "restrictor". Why are you going to go to that trouble? I would assume that you are thinking about the potential to cavitate the cooling water as if flows through the restriction if it was a simple washer with a hole in it, i.e. a sharp edge orfice. Per Chris he is planning to use a 24 lb pressure cap, and this sets the system internal ambient pressure, actually the maximum ambient internal pressure, as long as this internal pressure it above 15 psi it cannot cavitate . Cavitation in water is caused by reducing the waters pressure below its saturated vapor pressure, which for water is one atmosphere i.e 14.7 psia let's call it 15 psi. If the system is at a system pressure of over 15 psi the water cannot cavitate.
Rex
Mark,
My thoughts about your concerns, in no particular order, as usual . . . . . . .
1/ I am determined to run a "pressure bleed system". Not just because it is foolproof, once properly sized, but because it is also low maintenance.
The system will be similar to the Cosworth system schematic above, but with some additions.
Since the K engine family has known cooling issues, Chris and I are agreed that preventing these issues from occurring in the MM is paramount.
2/ Yes, the radiator will need at least 1 bleed line.
3/ I'm not in favor of running only an electric water pump, for the reasons you stated. I want the higher pressure and more turbulent flow that the stock pump can generate.
4/ The cylinder head will need 1 bleed line at the front since the water outlet is at the rear. This is already done on the stock installation, so it will be relatively simple to plumb in.
5/ I just want to have a provision in place to install a "restrictor" in the outlet line if needed. I want them available in my toolkit at Bonneville, not something I wish I had brought.
My experience with washer type restrictors is mixed. I want to avoid negative "possibilities".
6/ 24# pressure caps are readily available for racing. But you are right, we can use less pressure. We can probably run 18# successfully and still have a bit of a "safety margin".
7/ The system we will use will be similar to the Cosworth system in the diagram above. There will be the aforementioned additional bleed line from the cylinder head.
And, there will be at least one additional bleed line from the upper radiator tank, for the purpose of bleeding any air from that portion of the system.
8/ Bleed lines will be 2/3 mm ID, possibly AN-3.
9/ The "suction line" will be 1/2" or 5/8" ID, possibly AN-10.
10/ The header/expansion tank will be between 2/3 pints capacity. Bleed lines to connect near the top, suction line to exit on the bottom.
Pressure cap neck to have a provision for a coolant recovery system.
11/ We will be running a coolant recovery tank, not just because we don't want to contaminate the salt, basically because I'm lazy.
12/ I not sure we need to run a swirl pot. It can be added if required.
13/ I think I covered everything . . . . .
I designed this type of "pressure bleed" system decades ago, mainly to solve cooling system problems inherent in British road racing cars. It is complex, but it works, every time, given proper component sizing and placement. In several instances, with more efficient cooling, we were able to run smaller heat exchangers to gain a weight advantage over our competition.
The system works because small amounts of constantly bypassed coolant keep the radiator(s) and engine filled, IF the expansion tank is sufficiently sized. Minor overheating can be avoided with the coolant recovery tank, because the system will draw coolant back in, as opposed to getting a "gulp of air".
I freely admit that this setup is undoubtedly "overkill" for Land Speed Racing. But I also am concerned about being held at the starting line with the engine running and the water temperature rising. I don't want to find out how much of an overheating this engine can tolerate without sustaining damage. That would be dumb, and expensive.
This year's Milwaukee Midget Racing Motto is "stolen" from Joe Madden, manager of the Chicago Cubs, who tells his players:
"Just get out there and try not to suck . . . . . . ."Well, actually, we want the pressure bleed system to "suck"! ! ! !
Waterboy