There’s a dirty little secret that lots of owners of really hot street cars don’t like to talk about: the amazingly short lifespan of severe-duty electric fuel pumps. Let me set up the scenario. Let’s say you’ve built a street motor that makes 700 hp. You’ve done your homework, kept the compression safe, used coatings, spec’d your carb, converter, camshaft, and intake manifold perfectly, and it’s time to swing that bullet between the fenders. Like the rest of the motor, you research your fuel pump, and choose one with plenty of margin. Then a month or two after you head down the road, the engine quits. A quick inspection reveals a burned-out fuel pump. It must be a fluke, you think, and replace it with a new or rebuilt one, only for it to do the same thing again a month or two later. Then it happens again. Your first inclination is to blame the company that built the fuel pump. It must be a bad design—you scream over the phone.
The problem, unfortunately, isn’t the pump, but the extreme dynamic range the pump is expected to work through. In a stock performance car like a Mustang GT, the pump needs to operate in a range between zero hp and 300 hp. It only needs to move approximately 150 pounds of fuel per hour at its max, and small amounts of fuel the majority of the time. By extension, a fuel pump on a 2,000 hp Pro Stocker needs to move about 1,000 pounds of fuel per hour. A pump like this can last several seasons without breaking, because it never needs to operate reliably for long periods of time at idle or light-throttle cruise. Our 700hp street motor above, however, is in a dangerous no-man’s land. It has to operate reliably for most of its life at idle and light cruise.
That last item is a big problem, because the fuel pump is cranking full blast all the time. You’ll discover that most fuel pump failures on big-dog street motors happen mostly during three situations: during extended driving, when it’s hot outside, and when the fuel tank is near empty (or in some combination of any three). At the crux of the problem is heat. All electric fuel pumps use the flow of fuel to cool and lubricate. When the fuel gets hot, either through high ambient temperature or repeated recirculation, the fuel pump throws in the towel. The windings in the motor just burn up. Let’s look at the three different situations listed above, and talk about ways to avoid them.
Extended driving is hell on pumps because you’re returning the vast majority of fuel being moved back to the tank. This is especially the case with fuel-injected vehicles, but also carbed engines with return-style fuel systems. Your pump moves a huge volume of fuel from the tank to the hot engine bay, then back to the tank, ad nauseum. At some point, the fuel gets so hot, it boils the pump alive. When the weather is hot, the situation is made twice as bad. The solution? Don’t wait until the fuel gauge says “E” to add fuel. Another thing you can do is to add a fuel cooler in line downstream from the fuel pump (just after it on the outlet side).
Any heat build-up in the fuel system is made worse as the total overall volume of the fuel is reduced. During a long trip, fuel dwindles away, and the remaining fuel absorbs an increasingly high heat load—a situation you’d never see in a Pro Stock racecar. If you think of the fuel in the tank as a huge heat sink, then it makes sense to also increase the size of your fuel tank, and to keep it as full as is practical. Swap that 8 or 15 gallon tank out for a 20-gallon tank and things will improve considerably.
Carbureted engines that have mechanical fuel pumps are largely unaffected by this problem, but keep in mind that vapor lock—the distant cousin to electric fuel pump failure—will come into play at some point. A large diameter fuel line all the way to the tank will help, as does a fuel cooler.
The last thing we’re going to suggest is one of Barry Grant’s new line of King fuel pumps. The Mighty Enduro pump (part No. 170043) is for carbureted cars, and the Mighty Sumo (part No. 170041) is for fuel-injected cars. Both are good for up to 750hp, and feature a new twin-gear design that replaces the previous trouble-prone Gerotor design. This last thing is important, as a twin-gear design is far more robust in the heat-related situations listed above. Both pumps are a model of simplicity, featuring neither shaft seals nor housing seals. Both pumps employ Barry Grant’s QQM (Quiet, Quality, Mesh) technology, for quiet operation, low maintenance, and easy cleaning. In street applications, both should be installed with Barry Grant’s optional billet-aluminum heat sink (part No. 178000), to reduce heat build-up and subsequent pump failure.
For more specs on the Barry Grant line of QQM Mighty fuel pumps, you can log on to www.barrygrant.com, or call 706-864-8544.