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Return Conversion Theory:

Setting aside all the other plumbing upgrades that are generally associated with performing a return fuel conversion... I want to explain just the basic WHY of a return fuel conversion, as a follow-up to my last post in this thread.

There are a couple reasons a return system can benefit your car as you approach the limits of your fuel system. A return conversion can increase how much fuel your pump can provide to your rails, and it can increase how much fuel your injectors can provide to your cylinders. How is this? Its not quite clear at first. Because the only real difference is that the regulator is now located in the engine bay.

Along the plumbing in your fuel system are sources of resistance, restriction, and pressure drop. This is much like you will find a turbo system, just how people talk about pressure drop through an intercooler. The RFS extracts the most from your fuel pump by regulating your fuel pressure AFTER various plumbing restrictions, rather than before.

Your stock fuel sending unit houses the pump, filter, and regulator. The regulator is "set" at 52 psi +/-. Your fuel pump is running constant voltage, and therefore is constantly pumping as much as it possibly can given the pressure resistance against it.

So it is regulating pressure at 52psi at the pump, before resistance and pressure drops. When the engine is consuming high volumes of fuel, and the flow has to increase dramatically to maintain pressure, you will begin to see the restrictions show their face through pressure drop, as pressure in the rails begins to fall while pressure at the pump stays the same (and shortly after pressure will of course drop at the pump as well). By moving the regulator up near the rails, if you set it at the same 52psi... the regulator will bypass less fuel because it is regulating after the restrictions. Because of this, you should measure a pressure at the pump that is higher than pressure at the new regulator in the engine bay.

With the RFS, we have effectively extracted more out of the same pump. Yes you could have used a bigger pump, but there are many reasons to not go larger on a pump than is actually needed, and that is why our cars didn't just come with 400lph pumps. But that is a whole different discussion.

If we have extracted more from the pump by reducing regulator bypass and holding pressure at the rails longer... that means getting more from the injectors by keeping pressure up. Also, higher pressure generally means better fuel atomization, therefore increasing efficiency of fuel injected, possibly requiring less to be injected for the same A/F.

Lastly, the aftermarket regulators in the engine bay allow us to hook up a manifold reference line to increase pressure by 1 psi for every psi of boost. This allows us to maintain static fuel pressure differential, rather than a static fuel pressure (which would mean falling differential and less fuel through the injectors and reduced spray pattern quality). I recommend connecting the regulator manifold reference line to a charge pipe just before a throttle body, to prevent the regulator from seeing vacuum. (VVEL engines do not have appropriate vacuum profile for regulator reference. It will work, but its not proper in theory).

SPAM: We offer what we call a Stage 0 RFS for the 370z. We call it a stage 0 because it is merely a return fuel conversion, and it doesnt touch the feed plumbing. Our greater stages with large billet fuel rails and upgraded piping and hoses is in the final steps and available shortly or could be put together for an immediate order if anyone was in a rush.

Keep an eye out for a detailed 370z fuel system tech and catalog writeup I am working on in my spare time! Also, like our brand new facebook page to get the first previews before we start posting about new products!
/SPAM

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