Idleness Is A Fuel's Desire

While carbureted fuel systems are usually of a "deadhead" design, with no return line, but merely a regulator determining the rate of fuel flow to the carburetor, there are advantages to switching to a return style system. Jesse Powell again; "There is much potential for improvement in flow and pressure control available by incorporating bypass regulators and return lines in carbureted applications. This is particularly true when fuel pumps that do not have their own bypass capability are matched to regulators that do. In the big picture, there's not a single fuel system performance standard that doesn't improve when converted from deadhead to return style. For example, by running a bypass regulator, the pump can be set to run at lower pressure, thereby producing more flow, drawing less current, running quieter, even lasting longer. Return style systems respond faster to fuel demand and do a better job of keeping the float bowl full of fuel."

Of course, that fuel, whether sitting in a float bowl or pumping through an injector, has to be as clean as possible and free from debris, that is unless you want your jets or injectors to become blocked in short order. This is what filters are for. In the past we've used those cheapo white or clear plastic filters in our fuel systems; you know, the ones that cost a couple of bucks each at most, though even they've done their job and prevented dirt and rust from old fuel tanks from reaching the carburetor, but if you're investing money in a decent fuel system you'll want to step it up a few notches. Of course, if you're using fuel injection, you won't be able to use cheap filters as they won't take the pressure. This is a good time to mention that you should ensure all fuel lines are fuel injection type and not general fuel hose, which won't stand the pressure of an injected system. You really don't want a flexible hose coming away or splitting while gas is pumping through it under pressure!

So what should you look for in a filter? For starters it needs to minimize pressure drop while still being able to filter the fuel, but most importantly a filter absolutely must flow whatever the pump flows, making it "invisible" to the pump, with no restriction. This is achieved through a combination of its porosity, measured in microns, and its surface area. While any filter with a micron rating lower than 100 is too restrictive for the suction side of a pump, on the pressure side (between the pump and the engine) at least a 40 micron rating should be used. In fact Aeromotive suggest going down as low as 10 microns here. Jesse Powell told us "We have very specific filters that we match to different fuel pumps. Some of our larger fuel pumps require a larger filter with more surface area than others. We know this because we have spent an enormous amount of time testing our fuel pumps. We should know that each specific fuel pump requires a minimum amount of filtration media to ensure there is no restriction or pressure drop. We do this because if these fuel pumps operate in their ideal scenarios, the durability and performance is dramatically increased."

Maintaining filters is important to your fuel system's life too. Aeromotive recommends cleaning or replacing the element after the first 5-10 run hours, stating that the dirtiest a system will ever be is before it is installed. Paper elements should be replaced, but stainless steel ones can be re-used after cleaning, and annual filter servicing isn't a bad idea.

One area of the fuel system we haven't mentioned yet is the hard lines and fittings. Try to avoid sharp bends when fabricating the lines, in order to attain maximum flow, and avoid running it near exhaust systems. 3/8-inch (or #6 if you're familiar with that designation) tubing is sufficient for all but very high-performance applications, where you may need 1/2-inch (#8). Obviously, any fittings should be the same internal diameter as the tubing, so as not to cause obstructions to the fuel flow. The same advice regarding sharp bends applies here, especially with 90-degree fittings! While we're talking fuel flow, how do you calculate the fuel flow rate for your engine, and which pump should you select? According to Holley, an engine requires 1/2 lb of fuel for every horsepower at wide-open throttle. With a gallon of gas weighing 6 lb, this translates to a 350hp engine requiring 175 lb, or 29 gallons per hour (gph). This will tell you the maximum gph-rated pump you should use.

Hopefully we've given you an insight into modern fuel systems, why you should use fuel injection spec flexible lines, what to look for in a fuel pump, regulator and filters, and what's needed should you want to switch from a carburetor to fuel injection. All the companies whose products are shown here have websites that can explain specific applications, so do a little research and be safe. Ruptured fuel lines or leaks don't mix with hot engines, exhausts, or sparks.