Flash back more than a few decades. It was a gorgeous late spring day. Temperatures were in the mid to high eighties. The t-tops were off. The writer’s big block Corvette was running at full song. Seemingly in an instant, the gas pedal went spongy. The rat motor stumbled a wee bit, and then simply quit. Did it run out of gas? No chance. I popped the hood in an effort to track down the problem. As it turned out the combination of a tight engine compartment, big compression (the factory LS6 was converted to LS7 internal specifications including 12:25:1 pistons) and big tube headers simply proved too much for the fuel delivery system – big LS6 OEM fuel pump and all. The fuel was percolating in the Holley fuel bowls as well as in the fuel lines. The recurring dilemma was eventually overcome with almost every band-aid fix known to man. But it was never wholly resolved. Aside from boiling the fuel, there likely wasn’t sufficient volume to satisfy a thirsty, big horsepower big block. In the end, the entire dilemma showed how easy it was (and still is) to get a modified car fuel system wrong.
Fair enough. But when it comes to race-oriented fuel supply systems, there’s no question that big is pretty much the operative word. Proof is the honking fuel pump you’ll typically find nestled beside the fuel cell in a NHRA Pro Stock racecar. The trouble is if you have a modified street-driven car – fuel injected or carbureted, then you’ll find yourself at a fuel delivery crossroad. You see, with a big cubic inch engine on board, or one with a serious power adder or two (blower, turbo, nitrous or even a combination of the three), there’s a definite need for plenty of fuel. On the other hand, those big monster pumps that feed something like a Mountain Motor Pro Stock drag car don’t particularly like to run for extended periods of time such as those experienced with a street driven car. They weren’t designed for that purpose. And once again, heat becomes an issue (this is really critical if the pump configuration doesn’t incorporate some form of return or by-pass system – deadheading pumps build heat in a big hurry). The foremost reason is there is nothing to cool the big electric motors used in these pumps.
So what electric pumps are designed for the purpose? You just have to take a look at a modern fuel injected cars and trucks for some insight. In those applications, the electric pumps are engineered so that the fuel runs through them. As a result, the fuel supply actually cools the pump as it operates. That means the pump in question can run pretty much wide open for as long as necessary (and as long as there is fuel in the tank).
Does this mean you’re stuck with one of those little itsy-bitsy in-tank pumps that are found on most late model vehicles? Not at all. Today there are a number of options out there. Several companies offer big in-line fuel pumps that are engineered so that fuel runs through them (for extended operation). Case-in-point is the MagnaFuel 625 pump shown in the accompanying photos. Another great example is the Weldon A-600 pump also shown in the accompanying photos. Both of these pumps offer a number of features you should look for when shopping for a pump:
Aside from the continuous duty capability, both fuel pumps are self-priming. That’s a big deal because it means you don’t have to worry about pump mounting. In fact, it is possible to install them vertically or horizontally (mount bracket included). When selecting a mounting location, it’s a really good idea to protect it as much as possible from road debris and direct exhaust heat. At the same time, you have to keep it away from moving suspension components. Safe locations can include a spot alongside the frame rail or on the rear axle kickup beneath the trunk.
Another bonus is the pump size. The MagnaFuel pump is physically rather small, measuring just under 9.25-inches in length (including the by-pass). Taking the mount bracket into consideration, the pump measures just under 3.75-inches in height while the body diameter is 3.00-inches. The Weldon pump is similarly (small) sized, measuring 8.5-inches long with a diameter of 3.00-inches.
Both pump configurations are also quiet. Now, that’s not a big deal for a street-strip car with a large displacement, barely muffled engine on board or an-muffled bracket car, but if you have something a wee bit tamer, there’s a good chance the drone factor from an electric pump can drive you nuts.
Internally, the MagnaFuel pump makes use of double support bearings and incorporates polymer wear plates (which obviously contribute to the low noise and smooth operation). The actual layout and construction of the pump eliminates the need for shaft seals. Without shaft seals, then there’s nothing to leak (aside from an O-ring, which as most know are regularly reliable).
Meanwhile, the Weldon pump is manufactured with a 304 stainless steel housing. The end caps are Mil-Spec black anodized billet aluminum. Internal components are 100% metallic (no plastic components) and the electric connections are located on the outlet side.
When it comes to fuel lines, the Weldon pump has huge -10 AN inlet and outlet ports. According to Weldon, you should not install fuel lines smaller than the ports on the pump. In addition, the 600 series pump is manufactured with full depth O-ring ports. That means you must use some form of straight thread (not pipe thread) such as AN, Mil Spec or SAE designed for use with an O-ring.
Weldon also goes on to tell us you should always consider the potential for pump cavitation. Cavitation will limit flow to the engine and at the same time, it can also cause catastrophic damage to the fuel pump. Weldon notes that installing this pump in series with a stock in-tank fuel pump will cause the pump to cavitate. The reason is the OEM pump and small OEM fuel lines tend to be a real fuel flow restriction.
One thing we mandated for our current application (a home-brewed, 565 cubic inch combination) was a pump that didn’t require an electrical step-down device to reduce current draw. For example, the MagnaFuel pump is based around a high-torque custom motor with very low current draw (12 amps at 45 PSI). Ditto with the Weldon A-600-A pump. It draws approximately 7 amps under normal carbureted use. This means, for many applications, you don’t have worry about increasing the size of the alternator in order to keep up with the draw on the battery. This also means you don’t have to wire in a relay for the pump (although you can). The other piece of the puzzle for some folks is the capability to rebuild it if necessary. The MagnaFuel pump is completely rebuildable with a simple O-ring and wear plate kit.
With that said, we’ll wrap it up for this issue. Next time around we’ll continue out look at the pumps, but we’ll also address regulating fuel, filtering it and we’ll examine fuel bowl capacity. All of these intertwine with electric pumps, and all are very important in big power street-strip car or bracket racer. Watch for it!