We've really been pushing the limitations of the stock G8 fuel system, so I figured I would start a thread on this topic. First, we want to share what we've learned so far with the community, so everyone can benefit. And second, we'll talk about what we have planned next and see if anyone out there has better ideas...
Stock fuel system
The stock G8 fuel tank is plastic, and uses two individual fuel pump canisters. There is a separate pump in each canister, on each side of the tank. The fuel system is returnless, and maintains a static fuel pressure of ~ 59 psi under all conditions. The stock fuel injectors are high impedance and stubby, and seem to flow in the ~ 41.5 pounds/hour @ 43.5 psi range.
The completely stock fuel system is very stout, and in our opinion will work just fine - even for highly modified cars -
as long as you stay naturally aspirated.
Add a little boost
Once you install any sort of power adder, the entire situation changes. Somewhere around 6 psi of boost (depending on your air/fuel ratio), the stock injectors will reach 100% duty cycle. You can still run them like this if you want, but we don't recommend it.
Install larger fuel injectors @ 6 psi of boost
Once you reach ~ 6 psi of boost, it will be time to upgrade to the Siemens 60-pound fuel injectors. These pieces are top quality, and will take you as far as you want to go. You'll need some custom ECM programming for these, and some electrical adapters too. This will give take you to somewhere around 9 psi of boost (depending on your air/fuel ratio), and then your fuel pumps will no longer be able to keep up. You'll see that your fuel pressure will start at ~ 59 psi and begin dropping if you stay at full throttle for more than a second or two. I've seen mine as low as 40 psi by 140 mph on the dyno, but I don't plan to push it any farther until the fuel system is beefed up some more.
Get much more serious @ 9 psi of boost
Above 9 psi, the stock fuel pumps and fuel line are completely inadequate. Working in conjunction with APS and B & R Racing, here is the best game plan we have been able to come up with so far.
1. Add an additional one-way valve to the stock plastic pump unit, so that more fuel can enter it.
2. Fabricate a small custom surge tank to be located in the trunk and run at zero pressure.
3. Reroute the stock feed line from the fuel tank into the surge tank.
4. Feed two small Walbro GSS392 inline fuel pumps from the surge tank.
5. Give each fuel pump a separate -6 Teflon line to the engine bay.
6. Install aftermarket fuel rails.
7. Install an aftermarket fuel pressure regulator.
8. Use the factory feed line as the new return line, running into the new surge tank.
9. Route a return line from the surge tank to the stock plastic pump unit.
10. Add more boost until completely satisfied.
We hope this thread is useful to the community, and we're open to any and all input others may have on the next stages of this project.
Ready for testing
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