Teague On Tech: Q & A with Bob Teague Nov/Dec 2023

As seen in Speedboat Magazine’s
Nov/Dec 2023 Issue.

High Horsepower
Carbureted Fuel System

Dear Bob:

I have a pair of older TCM 800 carbureted supercharged engines in my 382 Formula FasTech, which also has been converted from the original XR drives to Arneson Surface Drives.

I need to change the mechanical fuel pumps that are mounted on the engine blocks. The pumps have a label on them that says “Edelbrock.” Which Edelbrock pump should I use? Currently, the boat also has an electric Holley fuel pump as part of the system. What part numbers do I need for the mechanical and electric pumps? Can I do away with the electric fuel pump and just use a higher-volume mechanical fuel pump? Thank you!

Randy Davis
Stafford, VA

Above Right: Formula FasTech 382 with twin TCM 800 carb engines.
Above Left: Weldon regulator mounted on engine.

Hi, Randy,

I am very familiar with your 382 Formula. Your engines were originally built in 2001. I’m including an original photo of the engines in your boat (see to right).

Our experience over the years indicates that on engines above 800 horsepower the redundancy and volume provided by two pumps working in parallel is highly beneficial.

First, there needs to be a fuel filter head that has two fuel outlets to separately feed the electric and mechanical pumps. The filter head and filter itself must be capable of flowing at least 150 percent of the engine’s fuel flow requirements. We now use the FST Performance filter with our billet filter mount.

Dual regulator manifold for increased flow.

We have done the fuel systems several ways in the past but feel the best way is to use a higher pressure electric pump compared to the pressure output of the mechanical pump. This way, the bulk of the fuel is passing through the electric pump when the demand is lower. This fuel flow is necessary to cool the electric pump and prevent cavitation.

The electric pump does not have a check valve so fuel can flow backwards through it if there is no check valve in the system. So, if a check valve is not used in the system, the electric pump must always be running to prevent back flow of fuel and possible aeration. Even if a check valve is used in the hose going from the electric pump, the electric pump pressure must still be higher than the output pressure of the mechanical pump. The mechanical pump has check valves built into it so fuel cannot flow backwards through the mechanical pump even if the engine is not running. The output pressure of the mechanical pump is established by the tension of the spring or springs located on top of the diaphragm.

Above: Weldon dead head regulator on mounting bracket.

The correct mechanical fuel pump to use is similar to your Edelbrock which is a time proven design with 6 valves. Several aftermarket companies were producing the same pump until all the castings and tooling disappeared at one point. We now use a 6 valve fuel pump made by Baker Engineering that is a billet replica of the original design. It is available in low pressure (about 7.5psi) and high pressure (about 15psi). It is also available in a marine version with the fume tube nipple that enables a quarter-inch hose to be routed up to the flame arrestor so fuel would go into the carburetor in case there is a diaphragm leak. The part number 9372 is a 15 psi pump, and the part number 9373 is a marine version of the 7.5psi pump.

The two outlets on the filter head are plumbed separately to the two pumps so they are working in parallel and not in series. If you decide to use a high pressure electric pump, one of the ways to complete the plumbing is with a TCM fuel log that is also fed by the electric pump and has two Holley or Aeromotive regulators mounted on it (One of the these smaller regulators may not be able to provide adequate fuel flow by itself). Then each regulator will have a separate hose connected to it to supply each carburetor (on dual carb set ups like yours), or to each bowl on a dual feed carburetor.

For ultra-performance set ups especially with a single carburetor, we use a tee in the outlet of the mechanical pump which is supplied also by the high pressure electric pump then routed up to a part number A2046 Weldon “dead head” regulator that also serves as a manifold for supply lines to the carburetor(s) and can be mounted on an available stainless steel bracket kit.

Tee for single -8 fuel line to carb.

If you want to use a lower pressure pump without the need for a regulator(s), you can use part number 11212 Aeromotive marine electric pump or the Holley (red) part num-ber 712-801 marine fuel pump. Each of these pumps have a pressure bypass built in which is controlled by a spring. It is pos-sible to raise the output pressure slightly by stretching that spring a little.

When using the lower pressure electric pumps with the pressure raised to be just a little higher than the mechanical pump, install a tee on the outlet of the mechanical pump and connect the outlet of the electric pump to the tee. This way both pumps will be feeding the tee which either has two lines going up to the carburetor(s) or has a single line going up to fittings on a single carburetor.

FST Performance filter and mount.

The final way of providing an adequate fuel supply is the way it was done in your boat. You have a manifold on the outlet side of the mechanical pump that is also fed by the electric pump with a -8 hose. Then there are two -6 or -8 hoses going up to the hard lines on the dual carburetors. This system works well as long as the electric fuel pump pressure is slightly higher than the mechanical fuel pump pressure. The electric pump pressure can be adjust-ed a little by stretching the spring in the electric pump bypass as described above.

The true test of your fuel delivery system is that you can maintain at least 7 psi fuel pressure at sustained wide open throttle. Also, you should not see fuel pressure fluctuation on your gauge at idle which is an indication of electric pump cavitation or air entering the system on the inlet side from the tank pick up to pumps.

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