Fuel System (and Mods)

The fuel system of a GT40 is not like the normal automobile. Instead of the single tank somewhere around the rear axle, you get two tanks along each side of the vehicle. Long and narrow so the fuel can really slosh around. What more could you ask for?

The RCR system follows this convention with two tanks, one in each sponson. Fuel filler and venting at the front. Level indicators pickup and venting at the rear. Each tank is about 8″ x 9″ x 44-1/2″, the outer edge contoured to fit into the angled sponson. Volume is approximately 11 gallons per tank.

The tanks are removed through a hatch in the front wheelwell. The suspension must be removed to remove the tank.

However, there is NO baffling and the units are not designed to accomodate an in-tank pump. No method of mounting or containment is provided so you are left to figure out how to keep them in place and how to feed fuel to your system. So the fun starts.

Carburetion

The original system used a switch and a valve, controlled by the driver, to select which tank was to be used. The electrical switch selected the pump, the valve selected where the flow was from. The pump supplied adequate pressure for the carburetors, whether they be Weber, Holley or AutoLite. And the bowls of the carburetor provided the surge control when the vehicle cornered or braked.

Modern systems using a carburetor can be configured the same way. Not a big issue.

Fuel Injection

Modern day electronic fuel injection has come a long way in the last 50 years. Unfortunately, the vehicles from back then didn’t address some of the design requirements of the modern day system. You must provide high pressure fuel, CONSTANTLY, without interuption or decrease in fuel flow and pressure, or the engine performance is affected. Not a big deal til the fuel sloshes forward while braking into a left hand turn. Not a good time for the engine to go lean or die. However, there are solutions around this.

I chose to add baffling to the tanks. Some have used Open Cell Foam blocks or plastic balls to serve as a baffle. However these materials are often affect by the ethanol in todays fuel. I added welded aluminum baffle plates, more details further in the article.

The next issue is the high pressure system. I chose to use an Aeromotive Phantom 340 fuel system. It provides the high pressure pump, located in a fuel reservoir so it is constantly submerged. Others chose to use two lift pumps to feed a ‘swirl pot’ which then contains the high pressure pump to feed the system. This involves not only the swirl pot but mulitiple pumps, check valves and piping. It just seemed way to complicated a way to marry two tanks.

I chose to tie the two tanks together with a cross-over line so fuel would transfer from side to side using gravity. A little research and a little help from ChatGPT, I learned a 16AN line tying the bottom of the tanks together would equalize in less than a couple seconds. More than enough time for the level sensor to work properly and to keep fuel available to the Aeromotive pickup system. And the pressure overflow gets directed back to the main tank so that side of the system is setup properly.

Cross-Over System

There are three places you can tie the two tanks together.

Thru the passenger compartment, under the knees of the driver and passenger. This is the way some of the MkII’s were done. I wasn’t real wild about having fuel passing thru the passenger compartment
At the forward end of the engine compartment, the line can be placed along the opening wall. A compromise must be made as it need to go under the lines coming out of the spline and accessibility through the sponsons if not easy.
At the end of the tank, with the line going to the rear and around the front of the horseshoe. This adds more stuff in an already crowded area and a knowledgeable plumber friend expressed concern that this path would work with the potential for an air bubble to block the flow.

I opted for the middle. Now, how do I get the line thru all the sponson walls.

I decided to bore holes thru the aluminum and with a little layout, I determined I could have a 1″ NPT bung at the lower edge of the side of the tank and the angle the tank sits at normally would enhance flow thru this bung. The angle also assisted in a slight radius in the line to assist in connecting the fittings. The low point of the line would be where it passed under the spline opening.

Boring a hole with a hole saw on an angle is not easy. I made a ‘support’ for the body of the holesaw to lay in as I bored thru the engine bay sponson wall. The remaining wall(s) were a little easier, but the whole process is complicated by the lack of room to work

Pictures of the installed hoses will be added later

Fuel Pump

I have succesfully used the Aeromotive Phantom system in two different cobras. They operate flawlessly, the only real issue is they are a little pricey. But when compared to the cost of multiple pumps and piping, maybe not.

Getting the system into the drivers side tank required modification of the rear top of the tank. I cut away the RCR fittings and added in a new formed top. The opening for the pump will be added after final welding and pressure testing, that way I don’t have to worry about how to seal the large opening.

Baffles

It is important to keep fuel in the system from sloshing around. A typical fuel tank is only a couple feet long and has baffles within that span. I chose to add two baffles into each tank which would form a compartment about 12+ inches long.

The baffles would be 1/8″ thick and inserted from the top. I slit the top of the tank into thirds so the plate could be inserted into and down so tabs on the bottom would enter matching holes in the bottom of the tank. The holes and slits were then welded closed