Ok, that's the direction I was leaning. Didn't think about the cavitation in the pump. I was thinking hot spots/air pockets in the block from boiling due to less system pressure.Larry Sockwell wrote:It helps keep the water pump from cavitating and raises the pressure in the block just a bit more than what you see in the radiator.
I appreciate the information and the link. I'll give it a read. I didn't expect I'd get these responses and your is interesting and colorful too. lol I was wondering if the restriction, at least, had something to do with the block/heads having hot spots, boiling, creating air pockets and the results of which. Thanks!Tuner wrote:http://www.motorsportsvillage.com/forum/viewtopic.php?p=46904#p46904
The deal with water pumps, electric or engine driven, and thermostats or restrictors, is less mysterious if you know the information Howard Stewart and Edelbrock published in magazine articles in “Stock Car Racing” and “Circle Track” magazines about 15 or 20 years ago. They made water pump dynos and measured flow and pressure vs. RPM and power required with different restrictions of thermostats or restrictor discs and different radiator designs.
The ‘ah-ha moment’ was in understanding that the OE type engine driven pumps pressurize the system several lbs. per 1000 RPM. I recall 10lbs per 1000RPM when the pump is 1 to 1 with the crank, but that seems like a lot, it’s been a long time since I read the information. Put a pressure gauge on your cooling system and see. The caveat in this is you must have a pump with matching volute and impeller shapes and the clearance must be tight, just a few thousandths like a jet boat pump. The stamped sheet metal impellers won’t geturdun.
Without the restriction of a thermostat, the radiator core is the restriction in the system. The restriction of the thermostat or restrictor disc is necessary to isolate the pressure to the engine water jackets so as to not push open the radiator cap and blow the water out at high engine speed. This is where the old wives tale of “the water goes through the radiator too fast to cool” comes from. Remember, if it’s too fast through the radiator to cool, it’s too fast through the block to get hot, opposite sides of the same coin so to say. With old top-tank vertical flow radiators, when the core becomes the restriction because the thermostat isn’t there to do the job, the unrestricted pump pressure blows the water out the cap. If you look at cross flow radiators the cap is nearly always on the suction side of the core. Stewart mentions some of this on his website but the old magazine articles had more details.
Obviously, it’s desirable to have the coolant pressure high as practical to raise the boiling point. During a ‘Cup’ race on ESPN recently, I thought I heard the guy with the cut-away car mention a 45 lb. radiator cap. I can tell you from running a boat with a non pressurized cooling system, once the water boils in the heads you have to stop and wait for it to cool because all the water in the world won’t cool the vapor around the exhaust valve guides enough to cool them. Like water dancing on a hot griddle, the liquid doesn’t touch the metal until it’s below the local pressure’s boiling temperature.
I recall about 5 HP was necessary to turn one of the pumps 6000RPM. 1HP = 746Watts x 5HP = 3730W ÷ 12V = 310Amps, and that’s assuming 100% efficiency which isn’t possible. How many amps do the electric water pumps draw? Essentially, a starter motor is needed to power a water pump in any kind of continuous duty.
I guess it’s OK for drag racing to use a pump that’s incapable of pressurizing the engine when you could make a pass without water at all. Back in the day, there were stories of Grumpy dumping both the water and the oil for the money round. Pesky fluids just slow you down. Short attention span racing is over before it starts anyhow.
An engine is a sorry SOB if it hasn’t enough power to pump its own water (and fuel for that matter). What’s next, electric dry sump pumps? CNC Manufactured Billet Anodized Programmable Pulse Width Modulated Solar Wind and Wave Powered Dry Sump Systems, LLC. Get your order in early, avoid the Xmas rush.
That’s mine, what’s your opinion?
Tuner wrote: This is where the old wives tale of “the water goes through the radiator too fast to cool” comes from. Remember, if it’s too fast through the radiator to cool, it’s too fast through the block to get hot, opposite sides of the same coin so to say.