Pumping Losses

Is Your Water Pump Costing Power?

Mike Petralia Mar 18, 2005 0 Comment(s)

We hardly ever think of them, but they're up there. Pumping away all day without care or complaint. Their pumping sounds blend in so smoothly with the purr of our motors that it's easy to forget they're even there. Quiet thieves is what they really are. Power robbers without remorse or regret. That's right, our water pumps are stealing power! But, is there anything we can do about it? You bet there is. Since we don't know of anyone who has figured out a way to run an engine without using at least some type of coolant pump, we'd guess that means they're pretty much a necessary evil that we're all stuck with. But in our constant quest for ultimate power, how can we afford to ignore these pumping losses? Luckily, the aftermarket has tackled the problem head on. They give us electric water pumps.

All of our Chevy engines have run a belt-driven water pump since birth, so one would not be mistaken to think that a belt driven pump is the only way to go. But that's like saying just because you were born with brown eyes that you couldn't make them blue. Not true in both cases. The world we live in today gives us choices. And the choice to run an electric water pump might save you some power, but it could cost you something more. You see nothing's free in the power-building world. What makes power for you in one area, can extract a price in another. While the power benefits of an electric water pump can hardly be denied, the costs of running one on the street can be harsh. Overheating would be your main cause for concern. That's because, while most stock and aftermarket belt-driven pumps can flow as much as 100 gallons of water per minute and racing pumps can flow even more, most electric pumps flow less than half that amount. It's a simple matter of physics and a giant paradox of performance. In order to flow enough water through the system, the pump requires a power source strong enough to move a large quantity of liquid. The gains from moving lots of water through the system are better cooling. The losses are measured in horsepower. An electric motor, on the other hand, does not cost horsepower to run, but instead it trades volume for power and cannot flow as much water. If you built an electric pump with a motor big enough to flow the huge volume of water equal to that of a belt-driven pump, it'd be so massive that you probably couldn't fit it under your hood. And the electrical power requirements for such a pump would make it impractical for use on any car.

So, clearly, the dilemma is: cooling vs. horsepower. And the path you choose will be defined by the use of your car. Street or drag? If you can afford a second car for your everyday commute and your hot rod only sees use on the weekends, then running an electric pump might be the way to go. But don't plan any long trips down the highway, because that's where you'll need all those extra gallons of water. Of course, you could always run a belt-driven pump and mechanical fan on the street and then switch to an electric pump and electric fan for the track, but is 10 more horsepower really worth all the headache?

There's also the option of keeping the belt and simply slowing down the pump, regaining some of that lost power by underdriving it. But, there are sacrifices there as well. Although we've proven that underdriving the pump does indeed save a few ponies, engines rarely overheat on the dyno. And they don't need an alternator to keep things charged up either. Those are two areas of concern if you underdrive a pump too far. There are all sorts of underdrive pulley kits out there, and most of them will add a little power to your engine. But if your engine is mild and idles very low, say under 800 rpm, cooling will suffer at those speeds. A water pump needs to spin to flow water and underdriving it means it might not flow enough at idle to cool things down. The problem will almost never show up when you're cruising down the road. Ironically, it will rear its ugly head when you pull up to a stoplight.

There are other options as well. One would be to rig up a quick-change system using a bolt-on electric drive, like the kits offered by Moroso, and swap the mechanical belt and fan combo for the electric combo the night before you race. It wouldn't be too much work. After all, you could probably leave the electric motor mounted to the engine and once you remove the fan and belt and bolt on the new drive pulley for the pump, all that's left would be to fabricate some quick clamps for the electric fan and run the wiring with something like Weather-Pak plugs. Another option would be to swap pulleys and belts to an underdrive system for the track only, which is almost as much work as bolting on the electric system and the few extra ponies it brings may not really give you an advantage.

We wanted to see just how much power a belt-driven water pump was robbing. So we bolted a healthy Mouse onto Dyno-Motive's DTS engine dyno and went to work. First testing a Weiand belt driven pump with both under and overdrive pulleys from March Performance, and then we swapped on a Weiand electric pump to regain our pumping losses. The results proved that there is power to be found in pumps and pulleys; you just need to know where to look.


How much power does it take to turn a water pump? We wanted to know so we bolted this stout Mouse onto the Dyno-Motive's DTS engine dyno for a test.

Under or over, that's how we planned to test the Weiand mechanical water pump. Using these billet aluminum pulleys from March Performance, we gained a little bit of power with the underdrive set on the left.

After testing we opened up the back of the Weiand mechanical pump to see what was inside. Its stamped steel impeller is hardly impressive, but the amount of water it flows sure is, and water flow is what a street car needs.

Eric Weinrich, owner-operator of Dyno-Motive has one of the cleanest, most well organized facilities we've ever seen. And Eric's pretty sharp too. We owe him and his partner, PHR Engine Masters Competitor John Beck, a big debt of gratitude for this test.

To make sure we didn't leave anything out, we first optimized engine power with timing adjustments. Turns out the Mouse liked 35 degrees total.

Weinrich also make a few adjustments to the Edelbrock 650 AVS carb, just to be sure power was at a premium.

The Weiand electric pump does not seal the bypass hole in front of the small-block, so we had to run a greased-up tap into the hole and install this plug to keep from spilling water all over the floor. The plug can be removed later if we want to go back to a mechanical pump, which uses this hole.


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