Fuel pipe size requirements for 700 BHP turbo engine

[Chris Wilson]

I know you Motec chaps see a lot of engine set ups, good and bad. I have built an all steel Nissan RB26 twin turbo Skyline race engine that could make 700 flywheel BHP on decent fuel. I am now at the stage of making the fuel system for it. It wont be running ethanol or methanol, just pump or "normal" race petrol. I am considering using a big Walbro in tank lift pump feeding a stainless swirl pot via -8 hose and a big -8 unioned filter. Twin Bosch 044 Motorsport pumps then suck from this pot via -10 lines and blow through two big -8 unioned filters, to a -8 T piece. A single -8 braided hose feeds one end of the fuel rail, and a -6 goes to the FPR and the from the FPR back to the swirl pot. The swirl pot has a top overflow return to the main tank in -6 hose and fittings. Should the -8 single main line to the rail be adequate? Everything else sound OK, I will be powering the two 044 pumps from the rear mounted battery with hefty cable and a 70 amp relay. Thanks.

[RossB]

This setup sounds ok to me. You need to make sure that your 044 pumps are at or below the level of the swirl pump as they are not designed to suck fuel and so need to be gravity fed. Once you have installed everything make sure that you test the installed flow rate by measuring the fuel flow from the return pipe to the swirl tank. You will have to do a short test (15-30 seconds) because during the test you will not be retuerning fuel to the swirl pot, then do a longer test (a few minutes) to check that the lift pump can keep up under peak torque conditions when there will be less fuel flowing through the return. I would also recommend that you install a good quality (e.g Honeywell) fuel pressure sensor and log the fuel pressure.

[Chris Wilson]

Thanks for that, system now made, just posted a question in this section with regard to fuel heating, if you have a moment I couldn't run to an electronic sensor and more wiring , so have fitted an in car mechanical fuel pressure gauge, which I hope will be better than nothing!?

[RossB]

A mechanical pressure gauge is not much better than nothing. A gauge is damped and cannot be logged. Think about how much money you have spent on your engine and how much it will cost to fix it if it detonates due to in-sufficient fuel delivery... a lot more than the cost of a decent pressure sensor!

[Chris Wilson]

You have persuaded me Ross, I'll invest in a Honeywell sensor and more wiring, I know in my heart it makes sense Thanks for your reply.

[Alex B]

Hi Chris,

Your fuel system should be Ok, although I would like to note that braided lines do smell. So if you don't want to feel like you sit in the fuel tank I would advise to use aluminum pipes in fuel system. The flexibility of the hose is really required where there is a need to get the fluid to the moving or vibrating part (engine) from the body. The rest of the system will be fine with pipes. We used to build cars with braided hoses fuel lines but they were hardly road cars given the fuel smell inside. Once changed to piping very little fuel odor is present so its useful as a road car. Most fittings suppliers offer aluminum pipes in 6,8 and 10mm diameters with wide range of applicable fittings, so its easy to build any system.

Regarding the fuel requirements I posted in your fuel temp topic.

Also I agree with Motec guys that you should get all critical parameters of the engine logged by the ECU or dash. You will be surprised how much you will discover when review the logs. I would go further and use following sensors.

Engine oil pressure
Engine fuel pressre
2 EGTs if you have twin setup
2 Wideband lambdas (again in case of twin setup)
Backpressure (could be used just for mapping)

Once more, so much is invested in the car its not wise to save on data logging and analysis.

Regards
Alex

[stevieturbo]

Ive been running my 044's via a 40A relay and 30A fuse for a few years now. Never had any problems. So 70A seems a LITTLE overkill.

I use a single -8 line to the front of the car into a small manifold that distributes to each of the 4 rails. I use a single -6 return line.

Ive flow tested this setup via the return, at 60psi base, 13.1volts test voltage for 20secs

It flowed the equivalent of 486 lph during this test. I couldnt achieve a higher voltage with the engine off. Even this was via jump leads from a running car.
at 12v flow was a good bit less, so I can only guess that at 13.8v it would be over 500lph.

SO take this into consideration when choosing your lift pump or swirl tank design.