Guys,
I've been meaning to talk about this for a while, it just seems that 24 hours in a day isn't long enough to get everything done, I want to get done.
Unfortunately that means my participation on the forums isn't as frequent as it used to be.
Let’s talk electric water pumps:
I have noticed more and more racers killing cylinder heads due to their use of electric water pumps. This phenomenon started a few years ago, and it took a little while for me to wrap my head around what was actually happening, then a little longer to prove my hypothesis.
Basically, the electric water pumps don’t flow enough volume to keep the cylinder heads cool. Now you may look at the advertised flow rates and argue that the manufacturer claims their pump moves 50 or so gpm. What they are not telling you, is that is a free flow rate. As soon as you ask that pump to push fluid through a restriction (like a block or cylinder head etc) the flow drops by approx. two thirds. Mechanical pumps don’t drop off near as much under the same circumstances.
The water temp gauge is showing the average coolant temp of water exiting the engine. With the reduced flow of the electric pump, we see localized hot spots in the cylinder head that are not reflected on the temp gauge. The most common occurrence is in the area between the two exhaust seats. This area gets extremely hot during a sled pull or drag race and if there is not enough coolant flow to remove the heat fast enough, the coolant temp in that area begins to rise faster than other areas of the cylinder head, as it rises, the pressure in that area also increases. As with all fluids, the tendency is to flow from high pressure areas to low pressure areas. As the temp and pressure increase in that hot spot, the coolant flow decreases or stops, as the fluid finds lower pressure areas to flow to.
The net result is that the aluminum begins to lose heat treat in that area, as the material softens, the exhaust seat gets pounded into the casting and loses concentricity to the valve guide, resulting in loss of seal between the exhaust seat and valve and eventually a loss of compression in those cylinders. In other cases, the localized overheating also causes an otherwise stable cylinder head to crack, usually in the exhaust ports.
Cast iron heads wont lose heat treat, they just crack.
Cylinder heads that have experienced this phenomenon will show perfectly acceptable hardness numbers everywhere except around the exhaust seats.
I had one customer that was convinced his dual electric water pumps were more than adequate. I asked him to perform a simple experiment: Remove the thermostats from a truck with a stock mechanical pump and also disconnect the upper radiator hose from the radiator and aim it over the top of the radiator and out the front of the truck. Start the truck and run it up to about 3,000-3,500 and observe how far the fluid is expelled from the truck. Perform the same experiment on his race truck with the electric water pumps. The difference in flow was astounding.
Our new engine dyno is outfitted with digital flow meters for coolant, oil, and fuel. Once we finish the dyno installation, I will publish the flow numbers of all of the commercially available electric pumps vs mechanical pumps, as installed on a Dmax engine. For now, I recommend higher HP racers use a mechanical pump if at all possible.
We have options available for stock location and remote mounted mechanical pumps as do others I'm sure.
Guy
I've been meaning to talk about this for a while, it just seems that 24 hours in a day isn't long enough to get everything done, I want to get done.
Unfortunately that means my participation on the forums isn't as frequent as it used to be.
Let’s talk electric water pumps:
I have noticed more and more racers killing cylinder heads due to their use of electric water pumps. This phenomenon started a few years ago, and it took a little while for me to wrap my head around what was actually happening, then a little longer to prove my hypothesis.
Basically, the electric water pumps don’t flow enough volume to keep the cylinder heads cool. Now you may look at the advertised flow rates and argue that the manufacturer claims their pump moves 50 or so gpm. What they are not telling you, is that is a free flow rate. As soon as you ask that pump to push fluid through a restriction (like a block or cylinder head etc) the flow drops by approx. two thirds. Mechanical pumps don’t drop off near as much under the same circumstances.
The water temp gauge is showing the average coolant temp of water exiting the engine. With the reduced flow of the electric pump, we see localized hot spots in the cylinder head that are not reflected on the temp gauge. The most common occurrence is in the area between the two exhaust seats. This area gets extremely hot during a sled pull or drag race and if there is not enough coolant flow to remove the heat fast enough, the coolant temp in that area begins to rise faster than other areas of the cylinder head, as it rises, the pressure in that area also increases. As with all fluids, the tendency is to flow from high pressure areas to low pressure areas. As the temp and pressure increase in that hot spot, the coolant flow decreases or stops, as the fluid finds lower pressure areas to flow to.
The net result is that the aluminum begins to lose heat treat in that area, as the material softens, the exhaust seat gets pounded into the casting and loses concentricity to the valve guide, resulting in loss of seal between the exhaust seat and valve and eventually a loss of compression in those cylinders. In other cases, the localized overheating also causes an otherwise stable cylinder head to crack, usually in the exhaust ports.
Cast iron heads wont lose heat treat, they just crack.
Cylinder heads that have experienced this phenomenon will show perfectly acceptable hardness numbers everywhere except around the exhaust seats.
I had one customer that was convinced his dual electric water pumps were more than adequate. I asked him to perform a simple experiment: Remove the thermostats from a truck with a stock mechanical pump and also disconnect the upper radiator hose from the radiator and aim it over the top of the radiator and out the front of the truck. Start the truck and run it up to about 3,000-3,500 and observe how far the fluid is expelled from the truck. Perform the same experiment on his race truck with the electric water pumps. The difference in flow was astounding.
Our new engine dyno is outfitted with digital flow meters for coolant, oil, and fuel. Once we finish the dyno installation, I will publish the flow numbers of all of the commercially available electric pumps vs mechanical pumps, as installed on a Dmax engine. For now, I recommend higher HP racers use a mechanical pump if at all possible.
We have options available for stock location and remote mounted mechanical pumps as do others I'm sure.
Guy
However im not in a posistion to swap back to a stock water pump. My rad is in the back of the truck and I changed where water goes into the block from drivers side to Pass side.
