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There have been several questions asked on the LocostUSA forum about details of how to properly connect up the fuel lines etc for a fuel injected engine. This article gives a brief description of how two typical setups can be done.
Keep in mind that there are many ways to accomplish the same result and this article is intended to help a first time builder who needs some basic help.
Comparison of fuel injection setup and a carburetor:
A fuel injection (FI) system function is the same as an engine with carburetors. That is, get the correct amount of fuel into the cylinders. Carburetors use various jets, air bleeds, mixing tubes etc etc to do the job. Some carburetors are quite simple (a model airplane engine might only have a needle valve) and others like a Weber carburetor allow you to precisely tune the device to your engine with many replaceable or adjustable parts.
An engine with a carburetor uses a low pressure fuel pump. The fuel pressure is typically 2 to 8 psi. The pressure only has to be high enough to maintain the correct fuel level inside the float bowl at any engine load. There is a valve in the float bowl that controls the amount of fuel that enters the float bowl. Unlike a FI system, a carburetor delivers the fuel mixture into the cylinder whenever the intake valves are open. While that time is rather short at high RPMs it is many times longer than the time a FI system needs.
The majority of fuel injection system nowadays depend upon a computer to meter the fuel to the engine using sensors that monitor the engine. The computer can very precisely deliver the correct amount of fuel under all conditions. A typical multi-port FI system has the injectors installed quite close to the intake valve. Typically the injectors run at 40 to 60 psi and deliver the fuel starting just before the intake valve opens. The time each injector delivers fuel varies from ~2 mS (.002 seconds) to 10 mS or more depending upon the power of the engine etc (obliviously a 3000 Hp drag engine is going to require a tremendous amount of fuel compared to a 50 mpg engine).
Fuel injection setup:
The fuel system consists of a fuel tank, a high pressure fuel pump with a filter on the intake side of the pump, high and low (return) pressure fuel lines, a high pressure fuel filter, a fuel pressure regulator and the injectors. In addition the injectors will have a final filter screen built into the injector body. And last but not least, the fuel computer and quite a few engine sensors.
There are two basic ways to mount the high pressure pump, internally in the tank and external to the tank. There are also various methods that the pump might use to pick up the fuel. For normal driving the pump pick up is located at the lowest point inside the tank. For racing there are various pickup locations and/or setups used depending upon what type of racing is done. For off road or track racing sometimes there is a secondary (small) container used that holds enough fuel so the engine doesn't loose fuel pressure during high G conditions. A low pressure pump is used to deliver fuel to this container. The high pressure pump would get it's fuel from the secondary container.
There are many variations and the Locouki system presented below is pretty typical for a road going Locost. Note that with an external fuel pump it is normally best to locate it so that it is as low as possible compared to the bottom of the fuel tank. For one thing you can prime the system the first time by leaving the end of the fuel line to the regulator open and put a little air pressure in the tank which will force the fuel to fill the high pressure fuel line which will prime the pump.
While there are some very good high pressure fuel pumps on the market I feel that some of them are very much overkill for a Locost. Usually in the pump specifications you will find the maximum fuel flow rate per hour and the maximum pressure the pump can deliver. As long as both numbers are higher than your maximum requirements the pump will work fine on your car.
Originally my car had a MSD pump that could pump 43 gallons an hour. It was very noisy and I really didn't need a pump that could empty my fuel cell in less than 15 minutes. If my car only got 5 mpg with my fuel cell capacity of 10 gallons I'd have to be going ~ 5 * 10 = 50 miles in ~15 minutes. That's 200 miles per hour!!
The pump does have to be able to deliver the volume of fuel required at your lowest miles per gallon rate. Drag racing would be a good example of the pump having to deliver a high flow rate for a short period of time.
So take an estimate (guess) of your lowest mpg as if you were going run that load (speed) continuously to arrive at the fuel capacity of the pump in gallons per hour for your car. Don't forget that when you are running at wide open throttle your mileage will be quite low.
As an example:
Assume your car would get 5 mpg during a 1/4 mile drag race and you did the quarter in 10 seconds. How much fuel would you require at that fuel consumption to do it for an hour? (5 mpg may be too high an estimate since that would be ~6.4 oz of fuel for 1/4 mile)
Miles traveled in one minute by repeating 1/4 mile drags for 60 seconds = .25 * (60/10) = 1.5 miles in one minute. That is equivalent to 90 mph.
Gallons per hour at 5 mpg is: 90 miles / 5 gallons = 18 gallons used in one hour. Add in a little safety factor and you should be OK.
Here is how the parts are connected up.
Note: Only one setup within the dotted lines is used. I have presented what a typical stock (donor) fuel injection plumbing looks like and what I have on my BEC car.
Description of Locouki setup:
The internal high pressure (43 psi) fuel pump is located in the fuel tank. I am using the stock Suzuki pump with a home made mount. This article describes how I mounted the pump. The construction of internal and external fuel pumps are different and one can't be used in place of the other. For one thing the internal pumps normally have a high pressure relief valve that dumps the raw fuel into the tank when the pressure goes above the dump point (perhaps 55 psi). If an internal pump were to be used externally you would have raw fuel being dumped all over the place if the valve opens. Not good if your brakes are really hot (like RED hot during a race!) or the car backfires!
An external pump generally is just not designed to be immersed in fuel and you are going into uncharted waters (fuel actually!) if you put it in the tank. You don't want an external pump inside your tank if it decides to have a melt down! Neither pump should be run with no fuel in the pump. The fuel actually lubricates the electric motor bearings and cools the motor. Trust me, they make a horrible screeching noise with no fuel in them.
Fuel lines, check valve and filter:
The red lines in the illustration are the high pressure fuel lines. The brown lines are the low pressure fuel return line back to the tank. This line has very little pressure on it since it is open at the tank end. I ran the open end about two inches from the bottom of the tank so it would not be spraying and vaporizing the fuel (since most of the time the open end of the pipe would be under the current fuel level). A check valve should be used to prevent siphoning of the fuel out of the tank if the line gets cut or the car flips over. My check valve is external to the tank but many fuel cells have an optional internal check valve that dumps the fuel out of the valve inside the top of the tank.
A high pressure fuel filter (white circle) should always be use on the high pressure fuel line. It could be plumbed just before the pressure regulator or as I have mine, between the regulator and the injector fuel rail.
Pressure regulator and return fuel line:
I am using an adjustable regulator (light green circle) that is mounted near the engine. Most stock (non-adjustable) regulators are mounted on the fuel injector rail to insure that the injectors have equal fuel pressure on them.
The pressure regulator requires a return line fuel line (brown) back to the fuel tank since the pumps are designed to pump much more pressure and fuel volume than the engine requires.
Parts list of my system:
Fuel pump ....................
Fuel tank ......................
Fuel pressure regulator ...
Fuel filter ......................
Stock Suzuki GSXR fuel pump w/modified mount (link to article)
JAZ, 24"L x 12"W x 9"H, 10 gallons w/foam insert
Stock Suzuki GSXR-1000