SL-C Manual: Fuel System
How you lay out and connect the fuel system is up to you, and will vary based on the kind of engine you select, along with its intended use. For example, a race engine will typically have two high-pressure fuel pumps in parallel for redundancy while a street car may have only one.
This section will focus on the popular GM LS-series of engines, but those with other engines will find the general comments useful in most cases, as the general principles are the same.
The basic outline is this: fuel tank to an inline shutoff valve, valve to a 100-micron filter, filter to a low-pressure lift pump, LP pump to an optional 10-micron filter, filter to a high pressure pump, optional 1-micron filter to the fuel pressure regulator, regulator to the fuel rail.
Most GM LS-series engines feature a returnless or “dead head” fuel system so that only a single fuel feed line is required to the engine. A regulator is used to modulate the fuel pressure seen at the fuel rail. The regulator can be situated down near the fuel tank and the fuel returned directly out of the regulator back into the fuel tank (or surge tank).
The fuel tank is designed to be offset to the passenger side to assist with weight balance.
A popular approach is to position the major fuel line components beside the fuel tank where there is space on the driver’s side, being careful to allow enough room for the battery, especially if you are using the Infinitybox SL-C-specific wiring harness which assumes that the battery is located there. However, this makes access and maintenance more difficult; a better place for the fuel system components is on a fabricated panel on the driver side of the chassis.
???Will please discuss surge tank in lead paragraph; make hose type recommendation.
Although the fuel tank is baffled, you should install a fuel surge tank and a separate lift pump from the main tank to prevent surge in the main tank from affecting supply to the engine. A surge tank is included as part of the kit in later cars. Failure to use a surge tank will result in starvation during cornering, even at moderate speeds.
If you are fitting a surge tank, you should return fuel from the regulator to the surge tank. The surge tank has an overflow connection that returns excess fuel to the main tank.
The regulator should be positioned so that its fuel pressure adjustment screw can be accessed. Also, keep enough free area around the appropriate regulator fitting so that a fuel pressure gauge can be connected if required.
Many builders find that two fuel pressure gauges are useful when their system includes one or more low pressure pumps that feed a surge tank. These gauges are available from the usual sources (Jegs and Summit) and while they cannot be seen while driving, they are often useful to diagnose fuel supply issues at idle with the rear shell open. In most cases, you will want a 0-15 PSI gauge for the low pressure side, and a 0-100 PSI gauge for the high pressure side. The picture below shows a system with only a high pressure gauge.
The preferred approach to connecting to the factory GM fuel rail is to use a stainless crimp type AN adaptor. This style of adaptor can be purchased from numerous speed shops like Jegs or Summit. The fuel rail can be rotated and swapped so that the fuel entry point can be either on the passenger or driver’s side of the engine bay. If you decide to run hard tube for the fuel line, run a short flexible fuel connection from the engine to isolate the engine and rail from vibration relative to the chassis. The photo below shows the fuel line connection with stainless crimp connection.
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Recently, the Superlite factory has produced a kit that has all the required pumps, filters, hose, fittings, valves, etc. on one easy-to-install aluminum plate that bolts to the chassis rails. The idea is that you mount the plate to the car, hook up the inlet and fuel rail, connect the pump wiring, and your fuel system is done. See more information here.
It’s a good idea to use a fuel sock at each tank pickup point. These do a good job of keeping the larger particles out of the fuel system (see picture). These can be obtained from Pegasus, Jegs, Summit, etc. They fit into the tank, usually at the end of a small hose at the pickup points.
When designing the fuel system layout, plan the installation so that fuel filters can be easily changed.
When the car is first started, you should plan to replace the fuel filters after the first few hours of operation, as inevitably there will be debris in the system. There may be a need to replace them several times until all the grit, etc. is captured.
When fitting any new fuel tank, including the one provided in the kit, you should assume that it is not clean and should clean it before use. Typically, tanks are cleaned by removing them from the car, filling them about 1/3 full of water, and repeatedly tilting the tank so that the water can catch loose shavings, dirt, dust, etc. in the tank. Drain the water and debris and repeat the process until you no longer see debris coming out of the stream. Repeat one last time with solvent, and let the tank dry thoroughly before you re-install it.
The amount of grit and dirt in the tank may be reduced by taping over the openings until they are ready to be closed off with hoses, etc., but you should always plan to clean the tank before use even if you tape the openings.
Once you have cleaned the tank, close off all openings to keep it clean.
Once you are sure the tank is clean, it is a good idea to test it for leaks. While rare, these sometimes do happen, and it is much easier to detect and repair when the tank is out of the car.
To test the tank, seal all the openings and pressurize the tank to no more than 5 PSI.
When it is under pressure, take a paintbrush and “paint” a soapy water solution over all the seams. Check every inch of every seam carefully, and if you see bubbles, you have a leak there. Leaks can be fixed with specific fuel tank leak-stop products available at parts stores like NAPA.
If you don’t see bubbles, and the tank retains pressure over a few hours, you have a proven good tank!