Fuel System

I'm learning a lot about building the SLC. Here are some of the things I learned about the fuel system and how mine has come together:

- Because of the design of the tank and the significant acceleration possible with the car, it is possible to unport the fuel pickup, especially when the tank is less than full. To address this, it is necessary to add a surge tank.
- The surge tank acts as an intermediate, or header tank. It is typically a tall cylinder, so that hard starts and stops can't push the fuel away from the pickup at its bottom.
- Two fuel pumps are required: one to feed the surge tank (can be low pressure) and one to pump the fuel from the surge tank to the engine (must be high pressure).
- A fuel pressure regulator is needed to control the fuel pressure.
- The LS7 engine (and I think all LS engines?) have a "returnless" fuel system, which means that excess fuel does not flow through the fuel rails and back into the fuel tank. Instead, excess fuel bypasses the regulator and flows back into the main tank from there.

Attached is a diagram which originally appeared on another thread in this forum. The diagram shows a fuel/surge tank layout that was the basis for the system installed on my car, although the fitting sizes indicated on the diagram are not the same.

I wanted to keep the installation compact and preferably entirely in the space beside the fuel tank, behind the driver. At the same time, the fuel filters needed to be relatively accessible for cleaning/changing. In this installation, everything can be accessed from the engine side of the car, although some disassembly of lines is required in order to get the fuel pumps out.

I haven't hard mounted anything yet, in case I find that I messed something up. Also, the parking brake cables might route through this area, so until it is clear where the cables will run, I want to keep the components movable.

Wherever possible, I used single-flare aluminum lines, which were flared with an aircraft 37 degree flaring tool and a cheap $6.99 Harbor Freight bending tool (Tubing Bender - Save on this Manual Tubing Bender). The advantage of aluminum lines is that they are light, cheap, have a small outside diameter and last practically forever.

Tubing sizes come in 1/16" increments. "AN" sizes refer to 16ths of an inch, so an AN3 aluminum line has 3/16" outside diameter. Most of the fuel system components (e.g. pumps) have a 3/8" threaded end, for which the standard size fitting would be an AN6. Many of the connections in the system are larger than this, but as the pumps are limited to AN6, the larger lines and opening seem a bit unnecessary, but for the most part, I installed a line to match the fitting size most of the time.

In some cases because of either a required bend radius that was too tight for the bending tool or aluminum tube size, I used stainless steel braid rubber hose (Aeroquip AQP). The nice thing about flexible lines is that you can get special hose ends that have angles already incorporated into them. Some people prefer using the teflon style hose, as the rubber hose only lasts 8-10 years or so. However, some people have concerns about the teflon hose, which has an unlimited life, but which can develop pinholes due to static buildup caused by fuel flowing through the non-conductive hose (the static arcs through the sidewalls of the hose to the steel braid outside). It is possible to get conductive teflon hose, but I don't know much about those and so just stuck to rubber. I may change these to teflon when the time comes, although that will require getting hose ends as well (the fitting are not interchangeable between rubber and teflon hoses). Flexible hose is sold in "AN" sizes just like aluminum, although in this case, the "AN" designation refers to the equivalent inside diameter aluminum line; the rubber and teflon lines will be a larger outside diameter than the equivalent aluminum tube. In other words, an AN6 rubber line can be connected to an AN6 aluminum tube and they both have the same inside diameter, but the aluminum will have a smaller outside diameter.

The steel braid hose and fittings were acquired from Summit Racing (e.g http://www.summitracing.com/parts/aer-fca0603/overview/) and the aluminum tube and associated fittings from Aircraft Spruce (ACS), e.g: http://www.aircraftspruce.com/catalog/mepages/3003versatube.php?clickkey=17152

Starting with the fuel tank and moving downstream, the components used on my installation are:
- Finger Strainer (large): ACS $18.90 https://www.aircraftspruce.com/catalog/appages/fingstrainers.php
- Nipple AN911-3D: ACS $4.70 https://www.aircraftspruce.com/catalog/hapages/an911.php
- Valve: ACS $19.65 https://www.aircraftspruce.com/catalog/appages/minifv.php
- Fuel Filter #1 RUS-650133 Summit Racing $24.97 http://www.summitracing.com/parts/rus-650133/overview/
- Fuel Pump #1 Walbro GSL 392 Ebay $82
- Surge Tank CX Racing Ebay $75 Cxracing Universal Aluminum Fuel Surge Tank Nissan 300zx MR2 S14 | eBay
- Fuel Pump #2 (high pressure) Bosch 044 Ebay $184.44
- Fuel Filter #2 (same as Fuel Filter #1)
- Fuel Regulator Aeromotive A1000-6 Summit Racing $152.97 http://www.summitracing.com/parts/aei-13109/overview/

Both of the fuel pumps have metric threads, which requires an adapter fitting to connect to an AN line. The Bosch required one of these: http://www.summitracing.com/parts/rus-670510/overview/ and one of these: http://www.summitracing.com/parts/aer-fbm2245/overview/

The Walbro pump required two of these (one for each end): http://www.summitracing.com/parts/fra-491961/overview/

Also, the fuel pressure regulator requires o-ring fittings (3 of them) like these: http://www.summitracing.com/parts/sum-220166/overview/. A fuel pressure gauge is connected directly to the regulator: http://www.summitracing.com/parts/aei-15633/overview/

The top two fittings on the RCR supplied tank are 1/2" NPT. I used these fittings to connect them to aluminum lines: http://www.summitracing.com/parts/sum-220649/overview/


The flexible lines are from the top of the surge tank to the main tank (the overflow) and from the bottom of the surge tank to the high pressure fuel pump. In both cases, a 90 degree hose end was used to help make a tight turn. The bottom of the tank is AN10 and required this fitting: http://www.summitracing.com/parts/aer-fbm4034/overview/ and the top (overflow) of the tank is AN8 and required this fitting: http://www.summitracing.com/parts/aer-fbm4033/overview/

Two of the lines (the line from the first filter to the first fuel pump and the line from the bottom of the surge tank to the second fuel pump) route in the space underneath the main fuel tank. In order to prevent them from chafing on each other or the aluminum tank or body, they were wrapped with some old radiator hose, cut up the middle and secured with zip ties.

The main fuel tank vent line is not installed in the photos; I haven't figured out what to do with that, yet, so it just has a plug installed for now.

All of this makes for some expensive and convoluted plumbing, but the end result is reasonably compact and should hopefully prove to be good in service.

Fantastic write up and installation. The only thing I would think twice about is the fact that aluminum tubing is usually only used on drag cars as they travel a short distance on smooth pavement. Aluminum tubing really can't take the vibration/stress found in other forms of racing.

Pre fuel filters are usually 100 microns and post filters are 5 or 10 microns. A 40 micron filter on the suction side (before the low pressure pump) might cause problems.

Thanks for taking the time to write this up so thoroughly, always appreciated. I was wondering how the fuel compartment cover fits for you? From the pic it looks to me like the tank is too far forward, I had to move mine a bit towards the rear to get the koso level sender to clear the cover.

Nice write-up -- it takes a good bit of time to have web-links along with a well written technical narrative. Maybe I missed it, but do you have a manual fuel cut-off. Comes in handy when you want to change the fuel filters. fuel+shut+off+valve - JEGS High Performance

I see the fuel shut off valve in pics 5 & 6 (wonder what brand that is) but I also noticed there is a hard line from fuel tank to the chassis mounted fuel filter. I would think that should be a flex line since the tank is setup to float.

Thanks for the compliments, guys.

Mark: Good point about the tank moving relative to the first filter. The tank is mounted on rubber and the filter is mounted in a rubber clamp - the aluminum line between them could work-harden. I hadn't thought about that. I agree, it should probably be changed to steel braid. The compartment cover does fit - that was one of the advantages of using the 90 degree fitting on top of the tank. Eyeballing it, there is actually about 1" of clearance.

Ken: Aircraft use aluminum fuel lines except for the bit between the fixed firewall and rubber-mounted engine. Aircraft usually have more vibration than cars and the aluminum lines last as long as the airplanes do, so I'm not too worried about them in the car, except where Mark pointed out above.

I like the hard-line as it makes for a cleaner install. Did you consider using in-tank pumps. I prefer in-tank setups, but my car is not in-hand (is at RCR ready to ship). Without it here it is difficult to figure out what the options are.

I didn't really look at in-tank pumps, but others have, and some people have even installed in-tank surge tanks. I guess it depends on how comfortable you are with cutting the tank and re-sealing it well enough to avoid any leaks.

Wow, nice write up. I'd think it'd be difficult for the SLC to fracture the hard Al lines. Especially if you are not tracking it that often.
The in tank pump would need to have a sump or it'd be starved. that adds a fair amount of mods to the tank. We know the surge tank works in multiple builds, so looks like you have a winner.
Is your stunt planes fuel system this complicated?? Have you though of a build log? It would be great to have all this documentation in one place. It tends to get scattered after a few years.

The hard lines look great and as long as the two connections point are rigidly mounted with respect to each other, no problem. The concern that I would have is the grade of automotive fuel available. Here in the Midwest, all you can find is 10% minimum ethanol and alcohol can be corrosive to certain grades of aluminum. As long as the aluminum in the fuel lines is rated for alcohol use then go for it. I could be wrong but I do not think that AV gas contains alcohol.