Mechanical water pump or electric? It’s the question that continually arises among high performance and racing enthusiasts, and probably always will so long as the tradeoffs evident in each remain as they are.
Maintaining an optimum operating engine temperature is key no matter the application, and both styles of pump, in essence, accomplish the same task, but they do so in much different ways and with significant and not-so-significant tradeoffs. By and large, your decision rests on the intended use of the vehicle — is it a racecar or is it a street car? As we’re seeing more frequently these days, however, a high-horsepower vehicle is often a little bit of both, and that elicits further debate about the merits and drawbacks of choosing mechanical over electric and vice versa. If you’re running a true, honest-to-goodness street and strip machine, which is the right choice?
A cast mechanical pump next to a billet electrical pump from Moroso highlights the small but visible size difference between the two. But the variances between the two forms of pump get much larger from there.
With the help of Don Meziere of Meziere Enterprises and Thor Schroeder of Moroso Performance Products, we’ll be outlining the intended applications — and the limitations of — each style of pump and help answer this frequently asked question.
Mechanical and Electric: Comparing And Contrasting
Traditional mechanical water pumps have long been a reliable means of delivering water to the engine, where it circulates through cavities in the engine block and cylinder heads and returns back to the radiator. Mechanical pumps, centrifugal in design, are operated by a serpentine belt, typically directly off the crankshaft, and because the power needed to turn the pump is provided by the engine itself, there’s no shortage of flow volume available — given you buy a large enough pump to meet your needs.
Drag racers, by and large, rely on electrical pumps to allow them to cool the engine between rounds; nevermind that electric pumps also retain all of that expensive horsepower.
For a road-going vehicle that undergoes stop-and-go driving, sometimes for hours at a time, a mechanical pump checks off all of the boxes, which is why mechanical pumps are virtually standard issue on any and all production automobiles. But for racers and those focused on the ultimate in performance without compromise, however, there are drawbacks. Chiefly among these is that because the engine is the “motor” for the pump, there are parasitic losses in horsepower. And for some, especially for those trying to set records or achieve a specific performance goal, that’s a deal-breaker.
A billet aluminum Meziere mechanical pump. An automotive staple, mechanical pumps vastly outflow their electric counterparts at higher RPM. But in this day and age of advanced technology and design, their value in the high performance realm is gradually diminishing.
“The downside of a mechanical pump is that it robs a significant amount of horsepower to drive it, and that’s a real shame to give up precious horsepower considering how hard we work to make it,” Meziere says.
The downside of a mechanical pump is that it robs a significant amount of horsepower to drive it, and that’s a real shame to give up precious horsepower considering how hard we work to make it. – Don Meziere
This number can vary, but the general rule of thumb is about 8-20 horsepower — the pumps of 25 to 30 years ago were more on the high end, while newer aftermarket pumps, like those common on LS engines, are often less than 12 horsepower at high RPM. And this is where electric water pumps come into the conversation. Electric pumps, as the name implies, are operated by an electric motor rather than the engine itself, eliminating any drain on horsepower. Electric pumps can also be mounted remotely, in cases where space in front of the engine block is limited (we’ll get to that more in a minute). But beyond the horsepower element, the advantages for racers who see limited wide open throttle time are aplenty. For one, the pump provides an almost constant flow, and is also operational when the engine is off, allowing them to quickly cool things down in their pit area. Or, for a street and strip car, while you’re in the convenience store getting yourself some coffee.
Schroeder and Meziere cite drag racing as the ideal application for electric pumps, as consistency in flow is a vital element for such a style of racing. Moroso’s electric pumps provide as much as 36 gallons per minute of flow, and this volume is available to the racer even after they’ve cut the engine ignition.
The contrast, however, is that electric pumps in general, cannot produce the top-end flow volume that a mechanical pump can, and in some applications, particularly in boosted street cars, there just isn’t enough flow there to keep things as cool as they need to be. Although numbers vary, electric pumps will typically flow two to three times as much as a mechanical pump at idle RPM (because electric delivers a constant flow rate, while mechanical is scaling with engine speed), but once the engine rpm exceeds 3,000, the pendulum swings in favor of mechanical, and above 6,500, as Meziere shares, it’s “no contest” that mechanical is the clear winner in maximum flow.
Most mechanical pumps in V8 engine applications flow somewhere in the vicinity of eight gallons per minute at idle, and ramp to 70 gallons per minute at 6,500 rpm.
Remote water pumps can be the solution when a big engine is being transplanted into a space that was originally designed for a much smaller one. – Thor Schroeder, Moroso
Every pump, according to Schroeder and Meziere, has a specific flow curve — a graph that denotes the performance of the pump given any back pressure. When presented with back pressure, electric pumps will tend to “dead head” and stop flowing at higher RPM’s versus their mechanical counterparts. Mechanical pumps, meanwhile, have a maximum effective RPM — a point at which once exceeded, will cause the pump to cavitate, or create air vapor in the cooling system that dramatically reduces flow and quickly ramps up the amount of horsepower robbed from the engine.
The power draw demands from the battery with an electric pump is determined by the motor design of the pump. Meziere’s pumps use 200-watt motors that, at full load at 12 volts, can run up to 16.6 amps. Meziere says the typical observed load is more in the range of 9 amps for their standard pumps and 12 amps for the high-flowing versions. Moroso’s pumps pull 8 to 10 amps under load in a typical 12 volt application, making either brand suitable for use in race cars that don’t run an alternator.
We utilized a remotely-mounted electric pump on our Project BlownZ Camaro during a rebuild a couple of seasons back, largely out of necessity to make room for the supercharger and gear drive out in front of the engine. For many, including those building street cars, a remote pump can be the difference between the engine fitting in the car and not.
One can improve the flow of an electrical pump over the short term by increasing the voltage, but this will typically decrease the operational lifespan of the pump before it needs an overhaul, and more detrimentally, can introduce heat beyond what the motor can withstand and burn it up.
A remotely-mounted Meziere electric pump.
Another pro in favor of the electric pumps, as mentioned earlier, is packaging — they can be mounted remotely (ie. not on the front of the block itself) freeing up space in the engine compartment and, in some instances, serving as the difference between the engine fitting where you want it to and having to perform an extensive vehicle modification. Remote-mounting can also make physical access to camshaft timing adjustment easier.
“In instances of engine compartment packaging issues, running a remote electric water pump can free up space in front of the engine when a big turbo or blower is being used,” Schroeder says. “Remote water pumps can be the solution when a big engine is being transplanted into a space that was originally designed for a much smaller one. Remote electric water pumps have been used in conjunction with mechanical water pumps and by themselves for engine swaps and in kit cars when there is a rear mounted engine and a front mounted radiator.”
Interestingly, manufacturers say they tend to find that remotely-mounted pumps last longer, as well — a factor they believe is due to the internal electric motor windings, brushes, and seals not being subjected to the harmonics of the engine.
And, if it’s a matter of contention for the customer, electric pumps also tend to weigh less than their mechanical counterpart, although Moroso and Meziere didn’t share specific weights.
An electric pump in the engine compartment of a street rod.
Are There Alternatives?
There are, of course, some alternatives to simply choosing electric or mechanical, as well as methods for catering one option or the other to your application for a given use that perhaps it isn’t set up for right out of the box. There are also products designed to give the best of both world’s, but each is a matter of how much effort you want to put in to save a few horsepower.
Most mechanical pump manufacturers will know the speed at which their pump cavitates. You will definitely want to stay under that RPM. – Don Meziere, Meziere Enterprises
Anyone somewhat familiar with automotive engines is likely aware that a water pump can be under-driven as a means of saving horsepower, using underdrive pulleys that slow the pump operation in relation to engine speed. The caveat, however, is that you have to be mindful — and calculated — in doing so, so as to not end up with a pump that lacks the needed water flow volume at idle, which for a street-driven vehicle, is something it sees a lot of at stoplights.
“Most mechanical pump manufacturers will know the speed at which their pump cavitates,” Meziere says. “You will definitely want to stay under that RPM. We have seen several instances where under-driven pumps do not perform well enough at idle. That causes overheating at cruise speeds. This is one area where our mechanical pumps do very well. The reason is that our pumps, being 100 percent machined on both the body and the impeller, tend to have less internal clearance so the flow is better than a ‘loose’ pump at low speed.”
Moroso’s Electric Water Pump Drive Kit (Part # 63750) is a unique product that can be driven mechanically or with an electric motor, depending on your preference at a given time and place. The kit includes an electric motor and a pulley and serpentine belt to allow for switching back and forth between the two.
Of course, the water pump is only a small part of the equation for a street vehicle, as the engine (the source of the heat), the radiator, the air flow into and around the engine, vehicle speed, the total capacity of the cooling system, and the outflow of the exhaust system heat all factor in, making how far you can get away with under-driving pump an entire topic in and of itself.
If horsepower is truly that important to you, there’s also always the option of physically switching pumps, from mechanical to electric to go the track and then back for daily driving. Is the juice really worth the squeeze, though?
“I don’t think that it’s worth the effort in switching back and forth between pumps,” Schroeder says, as Meziere adds, “in my mind it should not be necessary. Any street/strip car is a good candidate for an electric pump, except for the extreme turbo applications. The prospect of dumping the coolant or water and re-filling at the track sure seems like a fun-killer.”
The last option, and perhaps the most feasible from a time and cost perspective, is Moroso’s Electric Water Pump Drive Kit (P/N 63750) that serves as a conversion kit, if you will, allowing for both mechanical and electric operation. The pump kit includes a 12-volt electric motor, two drive pulleys, a serpentine belt, fasteners, and a toggle switch, and is a best-of-both-world’s choice for those that want to put in the grunt work under the hood.
Electric or mechanical is one of the most frequent questions amongst enthusiasts, particularly those whose vehicles see both the street and the strip. And thanks to a trickle-down in racing technology, electric pumps are largely replacing mechanical for the majority of combinations.
I’ve Got A Street/Strip Car: What’s Best For Me?
So, what’s the final verdict in regards to pump selection for your street/strip machine? That, of course, largely depends on a lot of factors, not the least of which is the option you feel most comfortable with in regards to reliability and longevity. That, and, whether or not 8 to 20 horsepower really keeps you awake at night or not. But both Meziere and Schroeder are confident that, given the capabilities of their advanced design, that modern electric pumps can adequately handle the demands of most street car applications, given you aren’t out flogging your vehicle wide-open for extended periods in the Arizona desert in July.
Meziere states that electric pumps have performed admirably in the vast majority of street car applications, going on to share that “typically, we will recommend mechanical pumps be used for any towing application, any application where turbo boost exceeds 35 psi, and any naturally aspirated or boosted engines used for continuous wide open throttle and in excess of 600 horsepower. These are the places where block pressure and, more specifically, pressure in the cylinder heads, becomes important to avoid detonation.”
Any street/strip car is a good candidate for an electric pump, except for the extreme turbo applications. – Don Meziere, Meziere Enterprises
Meziere goes on to say, “our electric pump customers are usually impressed by the added horsepower at higher RPM and how cool the vehicle stays while driving around town. Our pumps have been used on many Drag Week vehicles and NMRA / NMCA classes where street driving is a requirement.” Meziere cites their standard duty electric pumps carrying a 2,500-hour life on the electric motor, while heavy duty pumps that flow 42 to 55 gallons per minute have a 3,000-hour brush life.
Schroeder echoes that belief, telling us, “Moroso has customers using electric water pumps in street and strip applications that are over 20 years old with 60,000 miles on them. We’ve had this type of customer call in, tell us how long and how many miles are on their Moroso electric water pump and order replacement seals for the pump. Not because the pump was leaking but because they were freshening up the vehicle’s engine and everything that’s bolted to it.
“Our electric water pumps have spent countless hours on the dyno during their design process as we’ve worked to create a water pump that can flow large amounts of fluid in a short period of time and keep up with the rolling requirements of today’s race-winning engines,” he goes on to share.
An electric Moroso pump was also used on our Project Biting The Bullitt 1965 Mustang, a supercharged 9-second machine that saw plenty of time on the freeways of Southern California without fault.
Meziere adds, in closing, that it’s important to take a good look at the vehicle and the intended use. “There are situations where a street vehicle will see many hours of low-speed use, and in such cases the fans, the size of the, radiator and a decent electric pump are all vital to keep things under control,” he says.
The reality is, today’s electric pumps are more durable and longer-lasting than ever before, allowing the technology — and the benefits of electric pumps — to trickle down from the racing world to your car. And as those at Moroso and Meziere believe, and as many enthusiasts have found, electric water pumps can be right at home on your high-performance street car just as well as they can on a dedicated drag car.