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Return lines would probably work better installed after the radiator and before the inlet to the pump.
The 5/8" hole works great in a 12-A turning 9,600 RPM with a smaller than stock crank pulley driving the pump. If in doubt, rig up a test pump and restricter and spin it at an RPM you will have it turning in your application.
One year we raced at Gratten Michigan when it was 40 degrees out. I put in a 190 degree thermostat for the race. It never opened. The three 1/8" bubbler holes in the edge of the thermostat were enough to cool the engine. So we ran the race with the coolant temps at 140 degrees. And that with over half of the radiator taped off. Worst case was at St.Louis with the air temps at 108 degrees. The driver had to back off the revs a bit to keep the oil temp under 220. Water was at 210. At Sun&Fun I have seen radiators so small I would not have attempted to taxi that plane let alone fly it. Many folks use only one inch ID coolant hose for everything.
Your results may vary. Warranty is voided if the box is opened. Pictures to follow.
In a message dated 8/20/2020 6:07:49 PM Eastern Standard Time, flyrotary@lancaironline.net writes:
Lynn,
I can relate to all you say having had the same problems with hydraulics. However although I should know better than question your advice,--- Is a 5/8 hole enough? The standard pipe is 1.3/8 inch which makes the 5/8 only about ¼ size without doing the actual maths?? I can put a restrictor on the outlet to the engine which will be the ideal spot to put the Turbo return water pipe in as there will be a “suction” at that spot. Lynn mate you worry me, but I have to bow to your experience,
Thanks to all again, Neil.
From: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Thursday, August 20, 2020 11:49 PM
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: [FlyRotary] Re: Water direction
-Cool the plug side first with the coldest coolant you can generate. You want the highest pressure available to be found inside the engine so as to avoid boiling coolant. Boiling point of coolant is a function of pressure and temperature. So, you can buy radiator pressure caps for racing up to 30 PSI pop pressure. So NASCAR can run 240 degree coolant temps and have the engine last for 4 hours. In olden times we broached little cooling fins around the back of the plug holes in the rotor housing. Others fly cut fins on a mill. But that just shows you that the biggest heat load is around the plugs. Others put coolant feed pipes right between the plugs for even better heat control. Do not change the direction of the coolant flow, in my opinion.
In 5th grade we learned that fluids are not compressible. True, but coolant contains bits of air in bubbles that we cannot remove. So the coolant appears to be compressible just like air. So, when we spin up the pump it compresses to some extent the coolant it is pushing through the system. So, in a closed system that means that the coolant on the suction side of the pump will drop to a lower pressure than that on the pressure side.
But low pressure in the coolant invites boiling (cavitation). Notice the lower radiator hoses on cars are larger in diameter than the upper (Pressure side) hoses. So in every car you see the exact same situation. It is then a universal problem with cooling engines.
I use a 5/8" restricter in the at the top water outlet to the radiator to keep that hole as the primary limit to flow rather than have the radiator or engine internals be the primary limit. This makes the engine internals operate at the highest pressure in the system. And reduces the pressure drop in front of the pump. At first I just replaced the stock thermostat with a restricter but later I welded the restricter onto the water outlet.
Many have told me that the wide open system will work better, but after 30 years of racing with no cooling problems.........I disagree.
In a message dated 8/20/2020 4:11:04 AM Eastern Standard Time, flyrotary@lancaironline.net writes:
Two thoughts I imagine that might create issues:
1. Energy transfer down due to delta T being lower, increasing the danger of nucleate boiling near the plugs
2. Creating a higher differential between the hot and cold sides of the engine producing increased expansion differences across the engine.
Question: Do impeller pumps that we use suck and push equally well? My guess is that they don’t.
If this doesn’t matter would it help with the physical layout to suck the water through rather than push it through?
> Looking today how to hook up my electric water pump. The simplest is to send the water reverse to a standard pump. I do understand the hot side and the colder side but with the water being changes every 1 - 2 seconds, does this really matter?
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