Ever heard the saying, "Water and electricity don't mix?" Though it obviously hints at the dangers faced when using electric appliances near a source of H2O, the learned amongst us know the truth behind this saying is actually a little more complex. (That is, while pure "distilled" water is not a particularly good conductor, adding anything to make a solution increases conductivity dramatically.)
Sneer at this loose analogy all you want, but such a multifaceted truth applies to the use of electric water pumps in automobiles. These items have become a popular upgrade for late-model Corvettes, said to offer some of the same benefits as time-honored bolt-ons such as cold-air intakes and converter-back exhaust systems (namely, increased horsepower along with easy installation). But many readers have probably been thinking, "What exactly does an electric water pump do, and is it right for me?"
We at VETTE are here to shed some light on the benefits and drawbacks of these devices, and we've lined up Meziere Enterprises, one of the largest manufacturers of water pumps of all kinds in the U.S., to lend us a hand.
From a physics and engineering standpoint, let's look at the differences between an electric and a mechanical water pump, as used on an internal-combustion engine. Just to dispel any possible confusion, electric pumps don't ionize, "electrify," or change the properties of the coolant they pump. Rather, it is their flow rates-and the amount of energy it takes to achieve these flow rates-that makes the difference between them and the conventional mechanical pumps fitted to nearly all cars and trucks on the road.
Think of a mechanical water pump as a slave to the engine: The speed at which its impeller turns is always proportional to engine rpm. The Meziere brothers (Dave, Mike, and Don), owners of Meziere Enterprises, know all too well that the design of any mechanical water pump is a series of compromises.
"It is difficult to design a mechanical pump that works well at both the high- and low-rpm ends of the spectrum," says Don Meziere. "A larger impeller with tighter clearances is going to move a lot of water down low, but once you start to turn fast, it's going to take a lot of horsepower to turn, and it's also going to begin to cavitate."
Though the term sounds like what happens to your teeth when you eat too many sweets, cavitation is a phenomenon in fluid mechanics. In a nutshell, it occurs when a flowing liquid subjected to certain types of motion transforms to its vapor state (in other words, boils-not because of high temperature, but because of low pressure). This gives rise to vapor bubbles within the coolant, which subsequently collapse. This is bad news. In addition to reducing the efficiency of the pump, the pressure waves created when the vapor bubbles change back to liquid can also cause pump-parts breakage.
According to Meziere, "Simply put, this separates the coolant and stalls out the flow in the system, greatly diminishing its capacity to cool the engine. The impeller turns so fast that the water can't get down the high-pressure [outlet] passages and starts to swirl inside the impeller chamber. It creates 'air' in the system, so to speak, though this gas is actually coolant vapor."
Even the best-designed impeller will create cavitation when spun at sufficient speed, especially when that impeller must also be able to move coolant at the slower speeds experienced when an engine is idling or during a low-rpm cruise. For obvious reasons, OEM water pumps generally are designed to perform better at this lower end of the spectrum, meaning their flow capability at higher rpm levels is not optimal. This is very much a concern on a modified vehicle that will be used for road racing, as it can easily spell overheating problems.
"On such applications, underdrive pulleys [e.g., a smaller crank and/or larger water-pump pulley] are a good option, since by spinning the water-pump impeller more slowly in relation to engine rpm, they are just moving the mechanical pump into the range where it is reasonable for it to work and not cavitate," says Meziere.
But before getting ahead of ourselves, let's touch on the other part of the equation: horsepower. Cavitation or no, spinning a given pump's impeller faster requires more energy per unit time. The desire to increase horsepower-as opposed to cooling-system efficiency-is why underdrive pulleys are used not only on road-race cars, but on street/strip cars as well. After all, overheating is generally not as much of an issue in a drag-race situation.
Think of it this way: It takes less energy to impart slower movement to the coolant, and the energy saved gets sent to the tires to provide acceleration for the vehicle. But, as Don Meziere says, "The problem is, on a street/strip car equipped with underdrive pulleys, what used to be marginal flow at low rpm is now insufficient flow. So while they may be great for a cooling system on an engine operating at high rpm, that same engine may have a cooling-system problem while being driven around town or during other low-rpm situations."
An electric water pump, on the other hand, can turn whatever speed it wants. Its impeller isn't connected to the engine's crankshaft (or, in the case of an LT1, its camshaft), but rather to an electric motor. When subjected to the near-constant 12V DC source of a typical vehicle's electrical system, an electric pump provides a constant flow rate that doesn't vary by engine rpm. This allows the use of an impeller design that is most efficient at that one turning speed.
In the typical street/strip application-or in a full-on drag race situation-electric water pumps step in to provide the ultimate cure. "[An electric pump] provides optimal flow during the variety of engine operations the typical street/strip car sees. You want it to be able to go down the street at 1,500 rpm, then also work well at 6,500 rpm on the track, and an electric water pump allows you to do both with maximum efficiency," says Meziere.
Let's be perfectly clear, though: Electric water pumps are only appropriate for certain applications, and this usually means street/strip and drag racing (although Meziere says they have also been successful in cooling small-block Chevys of up to 650 hp in circle-track racing). "Typically, our electric pump will outflow a stock mechanical pump by about 3:1 at idle, and the flow advantage is there all the way into the middle-rpm range. A well-designed and properly-driven mechanical pump will outflow our electric past about 3,500 rpm, but the flow of the electric pump in this range is still quite adequate for street/strip vehicles. The case would be different during the sustained high-rpm operation of many road-race situations."
A side benefit for drag-raced cars is the ability to run an electric water pump while the engine is off. This allows coolant to circulate through the entire system and quickly cool down the engine between runs.
Since their widespread use is fairly new, it seems appropriate to touch on how electric water pumps evolved into the popular bolt-on goodie they are today. We talked to the Mezieres a bit about how they came to design these pumps for the small-block V-8s found under the hoods of Corvettes. "We've been manufacturing mechanical water pumps for quite a while, but starting with the LT engines, we began playing with the electric technology because it started getting reasonable to do so," says Don. "The seal technology we employ really allowed the rise of the electric pump, as it provides excellent reliability. In turn, we have been able to raise the flow levels of an electric pump substantially through intensive CAD and flow analysis of the pump body and impeller."
Enhanced durability has also been paramount to the success of electric water pumps on street applications. Since their electric motors are subjected to the high temperatures of a cooling system and the vibrations of the engines to which they are mounted, they need to last a long time in order to be feasible on a car that may be driven many thousands of miles a year. The company says it performs destructive testing on a consistent basis in order to verify that its pumps can perform 2,600-3,000 hours before failing. "That's about 50,000 miles at an average 20 mph," says Meziere. "One of the things that really has helped is optimizing the armatures, making sure the engine vibrations don't damage the windings of the motor. This helps the practical application of electrical pumps to street vehicles as well."
Durability is great and all, but the bottom line for most readers is probably the horsepower increase. Says Meziere, "We usually advertise 11-14 hp as a conservative estimate!"
Double-digit horsepower increases sound pretty appealing-but let's not just take Mr. Meziere's word for it. What better place to test these claims out than on the king of all Corvette engines (at least as this is written), the LS7? With a lightly modded C6 Z06 donor car supplied by owner George Benson, and the top-notch installation/fabrication/tuning facility of TT Performance Parts in northern New Jersey, we were ready to get rolling with the installation of one of Meziere's electric pumps for LS-series engines.
Overall, the Meziere electric-water-pump installation took very little time and effort (the draining of coolant being the only somewhat messy part). Aside from meeting the claimed horsepower increase (at the rear wheels, no less), we also noted the very consistent coolant temperatures that Don Meziere spoke of, both on the dyno and out on the road. And let's not forget that with its ability to run independently of the engine, the Meziere 300-series LS pump provides control over engine temperatures not possible with a mechanical pump.
Freed-up power, super-consistent engine temps, and the ability to cool his LS7 in the staging lanes. With his new electric water pump, Benson is ready for his Z-car to assault the strip like never before!
After the Z06 is started and warmed to operating temperature, we make another dyno pull. The results: 482.0 horses and 459.2 lb-ft, for increases of nearly 13 hp and more than 10.5 lb-ft respectively-just as Meziere promised! As you can see, gains were recorded throughout the rpm range. Though some of this increase may be attributable to our use of a colder-than-stock 160-degree thermostat, we doubt it accounts for more than a couple of horses.