12/07/2004 |
C855 YVM - Robin Hood Exmo
Your next major stumbling block is the fuel system. With good old carburettors, you simply pump fuel into the carb(s) at (relatively) low pressure using an electric or mechanical fuel pump. Fuel injection, however, needs to run at comparitively high pressures (e.g. 60-90psi) and needs to maintain this constant pressure at the injectors. To do this, the injectors are fed from a common chamber (the "fuel injector rail") which is forced fuel at high pressure. At the other end of this rail is a regulator which bleeds off unused fuel. This regulator decides the operating pressure of your fuel injection system. Any fuel that passes through the regulator is returned back to the fuel tank. So, in effect, you have a constant loop of fuel running from the tank, through the fuel rail and back to the tank. The injectors are just "fired off" as necessary, thus dumping fuel from the rail into the throttle bodies. The amount of fuel that runs through the injectors is relatively small when compared with the amount of fuel being returned back to the tank. So the standard fuel pump as used with the original Ford Pinto engine will not do. Even an electric pump has to be specific - a high pressure model. This is no major problem and it doesn't have to be expensive. We purchased an electric high pressure fuel pump as used in Volkswagen Golf/Scirocco GTi's. This pumps out between 90 and 100psi (reliably, so I am informed) and cost just £25. Job done. Your next major problem is the fuel tank. The fuel tank provided by Robin Hood is pretty much just that - a tank. It has no internal baffling to stop fuel "sloshing about" when you go round a corner or brake sharp. Under most circumstances this is fine, but with fuel injection this introduces a problem. Remember we are now drawing fuel constantly at a greatly increased rate of flow... the fuel system needs to be constantly fed with fuel. With the standard tank and the standard fuel pickup, it's highly likely that hard cornering will see the fuel slosh to one side of the tank, leaving the fuel pipe picking up nothing but air. Not good.
To combat this we need to take fuel from the bottom of the tank (gravity fed) and we need to ensure that the area around the fuel pick-up is never starved of fuel. Racing types sometimes run a tank filled with a foam "sponge" that holds the fuel in place but an easier way to achieve it on the road is to put baffles in your tank - essentially you "compartmentalise" (is that a real word?!) the tank so that fuel is only ever sloshing around in a sub-compartment of the tank as opposed to the whole thing - think of it like an ice-cube tray... or maybe a diagram would explain it better!!  To solve this problem we thought, rather than chopping the tank open and trying to weld baffles into it, we'd weld a small "sub-compartment" onto the bottom and drill holes into the main tank to allow fuel to drain through. Any sideways movement of the car would mean fuel sloshed around the (large) upper compartment but fuel within the lower compartment should be far less likely to slosh upwards and out of it's chamber. This will mean the fuel pick-up will be kept fed with fuel with more consistency than if it were in the large upper chamber. At least, that's the plan. We'll let you know when it's on the road!!
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