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The Fuel Pump

Once you start to run some high boost (14-16 psi and over) on an upgraded turbo, you will be past the limits of the stock fuel pump, and more than likely close to, if not, maxing out your injectors. Replacing the injectors alone will not help, you will need to upgrade the fuel pump to a unit which can flow more fuel. Replacing the injectors can actually be avoided if the pump you upgrade to is capable of maintaining a high volume of flow at high pressures. An injector is rated as follows, NNNcc/min @ NNpsi. If you raise the pressure then the injector will flow more. For example if an injector can flow 450cc/min @ 42psi, and you raise the pressure to 52 psi, the injectors will now be 500cc/min @ 52psi injectors. The formula used to calculate this is after this paragraph. Obviously there is a limit as to how much pressure the injector can take, before the solenoid locks up. I would recommend that the injectors in the GT-Four are NOT run higher than 75psi. Don't forget to add boost pressures to your base pressure. For example if you run a base pressure of 52psi, and your maximum boost is 20 psi, then max fuel pressure will be 52+20=72psi.

(The Square Root of (New pressure/Old Pressure)) x Flow Rate at Old Pressure.
(Square Root of (52/42=1.238) = 1.11265) x 450 = 500.6

IThe part number of the pump is 0 580 254 979 I do not have any definitive flow information on the pump. However, I have received some info from a member of another list who did some checking, and came up with the flow of a similar Bosch pump. I was also informed of the following web page http://www.theoldone.com/components/fuelpumps/ which lists some specifics on the pump. Below is a table showing the flow of the pump. I make no garuntee that these figures are accurate, but what I can tell you for sure, is that the same pump is used in some 400hp Lancer Evolutions that rally in the U.S.A. I can also tell you that it flows plenty of fuel at approx. 70psi of fuel pressure. The reason for upgrading the pump was simple, the car was starting to lean out by 6,500rpm, and the injectors were at 100% duty cycle even before 6,500rpm. However after installing this pump, changing the fuel pressure to convert the injectors from 450cc/min to 500cc/min, and making the necessary changes to the fuel map, the car was running super rich, as in 10.0/1 air/fuel. While this is way to rich for good power, it isn't a problem, as I can retune the fuel map on the Autronic engine management system. It's also good to know that I have the safety of plenty of injector and pump capacity available.

The Installation

I decided that I wanted to install the new fuel pump in the tank, just like the stock one. It's a tight fit but the fuel pump assembly fits back into the tank, just barely though, and some manoeuvring is required to get it back in. In order to use the stock bracket, you will need to cut the metal fuel line that attaches to the pump exit. This will have to be cut fairly close to the top of the bracket. After you cut it, try and file the edge blunt, you don't want it cutting into the hose when you are sliding it on. I also used a screwdriver to flare the end a bit. You will need to purchase some fittings to screw into the entry and exit of the pump. For the exit you will need a barb to accept a 5/16 inch hose. On reflection, I think a 90º barb would have made the assembly fit into the tank much easier, and would only require a single bend in the fuel hose. For the exit you can purchase a fitting with threads on both sides that would screw into the entry side of the pump. You will need to get one of the ends machined down, so that it will fit into the stock fuel pump filter (see diagram at right), unless of course you can track down something that would fit straight into the pump and filter. The pump is held onto the bracket with a hose clamp. I would not recommend using cable ties or any other methods to strap the pump to the bracket. In order to get the assembly to fit back into the tank I had to do a little filing of one of the edges of the bracket. Obviously you will need to get some 5/16 inch fuel line. Note: Make sure you purchase fuel injection high pressure hose.