Filters For Your Fuel System

The first thing to know about fuel filters is how the fuel pump works. Fuel pumps, like nearly all pumps, push better than they draw. That is why OE electric fuel pumps are in the tank. Keep this in mind when plumbing any restriction (the filter in some cases) into the fuel delivery system. The smallest air leak in the suction lines leading to the pump will cause problems.

There are many ways, with different types of hoses and fittings, that the fuel lines of a race car can be assembled. Each connection must be tight and sealed. This, of course, includes the installation of the filter. The filter may be a one-piece, throw-away type. In this case, only the line connections need attention. Just remember to replace the filter when necessary.

When running rubber lines from the fuel cell to the engine, it is never a bad idea to use double clamps. This is not for strength but for sealing. Be aware that these small, commonly used hose clamps can be over-tightened. When this occurs, the rubber is squeezed out through the slots in the clamp. Too much of this can cut into the hose and actually cause a leak. I learned this lesson the old-fashioned way. I spent a lot of time finding this problem on the race car. With the take-apart, cleanable filters, the removable ends will have a gasket or an O-ring. Be careful not to damage these. An ineffective seal can cause a lot of head scratching while looking for a problem.

As stated, the location of a filter is important. If we put the filter between the pump and the carburetor, any trash from the fuel cell forward must go through the pump. The valves in the pump can take some abuse, but slow wear may be difficult to diagnose if it becomes a problem. This problem is most likely to occur on a new system. New lines, fittings, and so on should be cleaned before installation. Often, in the rush to get the car ready, this is neglected.

The solution is to use a low-restriction inline filter with a stainless steel screen between the fuel cell and the pump. Remember to install it in a convenient location for future cleaning. Then, a smaller filter with a finer filtering element can be put between the pump and the carburetor. This secondary filter will work well on the push side of the pump. Your carburetor will be happy, too. Some carburetors (Q-jets) have a very small filter at their fuel line attachment point. These are OK for the secondary filter, but they should be replaced more often because they are diminutive.

One thing to consider in filter selection is the type of fuel used. Any of the available filters work well with gasoline. Alcohol fuel is different. Any filter material that is not compatible with water is not compatible with alcohol. Paper filter elements absorb water. This does not stop the flow, but it can slow it down severely. If you are running a 10 percent ethanol fuel, there should be no problem as this amount of alcohol is absorbed into the gasoline base. With any fuel, however, a good choice would be an inline, cleanable filter with a stainless steel screen. These have low-restriction designs that work well on the fuel cell side of the pump. A less expensive paper filter can be used for gasoline only. In this case, a larger one would offer less restriction.

I spoke with some people at Holley Performance Products on the subject of filter elements. Oswald Baasch, a Holley fuel engineer, said the following: "Alcohol is hygroscopic up to a certain water/alcohol mix. If the mix is beyond the hygroscopic index, alcohol and water will separate. The hygroscopic index is highly dependent on temperature. Filter material is engineered for maximum efficiency according to the fluid to be filtered. I would be worried about filter integrity due to alcohol compatibility. Pleated [paper] is glued/crimped. Is the glue alcohol compatible? Paper filters usually use pleated end caps that are subject to corrosion, especially for water/alcohol mixtures."