600+ and fuel setup

Nissan370

Ok as I prepare to get deep into the 500 and 600 hp range
What are the reasons to go return style on my fuel system
And why would just staying return less be a bad idea
ATM I am using 340lph automotive fuel pump and 750cc injectors
I will be jumping up to a 950cc injector

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370z vsr motorsports single turbo/built motor 9.1cr 525rwhp/450rwtq @ 10.5psi (stock maf maxed out)

SPOHN

The problem with the OEM returnless system is that the factory fuel pressure regulator is installed in the fuel tank. The factory fuel pressure regulator does not allow fuel pressure adjustments and it can't hold consistant fuel pressure with high HP levels. The factory fuel pressure regulator is also unable to add fuel pressure under boost. With a return setup it removes the factory regulator's control of fuel pressure and replaces the control with a vacuum/boost sensitive adjustable fuel pressure regulator (under the hood). This allows you to adjust both the level of fuel pressure and increase fuel pressure under boost.

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Nissan370

So at what point are people changing over and are there any good kits out there

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370z vsr motorsports single turbo/built motor 9.1cr 525rwhp/450rwtq @ 10.5psi (stock maf maxed out)

SPOHN

Not sure exactly. I've seen some making 585 whp but not sure if there fuel pressure is dropping. So 550whp and up would be a good bet. But most don't make that unless build motor in which you'd want to that mod anyways.

CJ Motorsports is your best bet. They have been dealing with fuel setups for a long time on our platforms.

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Nissan370

thxs for the info. since i have a built motor this would be a good time to take care of that as well
i will go check out there site.
this would be a good over the winter thing to do along with my clutch and maf upgrade

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370z vsr motorsports single turbo/built motor 9.1cr 525rwhp/450rwtq @ 10.5psi (stock maf maxed out)

Mr.Squeeze

These are all smart upgrades especially your fuel system. You do not want the stock fuel pressure regulator dropping pressure while trying to make power.

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Driven Motorsports Single Turbo 7675 T4 1.32 A/R 995WHP 780TQ

phunk

I must apologize that our website is currently very lacking... we are finishing up a whole new fuel system catalog for the 370z. it will be all done before the new years... but a lot of it is already set to go and we have finished parts out being anodized.

I have to run right now but I am going to come back to this thread later tonight or tomorrow to help highlight some of the ups and downs of different fuel system modifications.

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phunk

Generally we tell people that the stock fuel system is adequate for 500-550rwhp (turbocharged). Thats not saying you couldnt squeeze more out of it with perfect or even less-than-perfect circumstances... but its not the best idea to consistently run a fuel system at its maximum capacity unless you are heavy into your vehicle tuning and logging and give it above average attention and monitoring.

But our power estimates are assuming all things in the engine are stock. Once you reduce your volumetric efficiency with lower compression.. you are reducing the efficiency of your fuel system as well.

For two reasons. The most obvious is the common sense that a lower compression ratio makes less output of the provided air/fuel mixture. So it will take more air and more fuel to get the job done. The less obvious reason is a side effect of the higher boost pressure it will take to get to the same power. Since you need to add more air to make the same power with lower compression, you will end up at a higher boost pressure to achieve the power. The higher boost pressure will reduce the fuel pressure differential.

The fuel pressure differential is the difference in pressure from your intake manifold to your fuel rail. Your factory fuel pressure is around 52 psi at the regulator (in the tank). Imagine your intake manifold operating at 52psi of boost... the injectors would merely drip fuel into the manifold when they open. That is just an extreme example to convey how intake manifold pressure has an effect on the delivery of fuel from the injectors. There are also effects on injector spray pattern, or fuel atomization, from operating at a lower fuel pressure differential.

These reasons and more have to do with why we are generally more comfortable pushing the stock 370z fuel system further than say the 350z DE fuel system, as the VHR motor is so much more efficient.

So while we say 500-550 for a stock engine turbocharged... it will be lower for built engines, and also lower for supercharged cars (superchargers consume power from the crankshaft before it makes it to the wheels). I wont say that people cant go further... they can and they will. Recommendations are just about when things are clearly safe. Running outside safety boundaries can mean inconsistency.. from car to car, or from day to day in the same car.

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phunk

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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phunk

Also I wanted to add that for any of you who choose to build your own custom RFS... We carry every custom billet proprietary fitting and adapter you need to interface with the OEM components wherever you choose to.

But once I show you guys what we built, I don't expect many DIY builds

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OldBoy

Car manufacturers don't put over sized fuel pumps on their cars for the same reason they go the returnless way... just to save a few bucks on each car made. It makes zero sense to use a returnless system over a return system apart to save money over component cost. I remember when I started doing my install on the Z and realized there wasn't any fuel return. The first thing that came to my mind was: "Why the F*** would Nissan do that!!", then I remembered that they didn't put an oil cooler on the car too... cheap bastards

Oh well, guess that just means I'll have to throw money at you Charles at some point in the future.

Also, this might be a bit of a dumb question to ask you Charles as I'm pretty sure you tested that already, but did you ever put a fuel pressure gauge on the fuel rails to see at what point the OEM POS returnless system starts to drop in pressure? I'm guessing by the 500whp mark its already dropping a few psi of fuel pressure??

1slow370

Actually there is more to not installing an oversize pump than just cost. Larger pumps circulate more fuel through the regulator so you need to design the regulator for the increased fuel flow, also because the pump is bypassing more fuel it will heat the fuel more, and hotter fuel means less dense fuel chargers which taxes the fuel system more and robs power. Also larger pumps draw more amps putting more load on the alternator. Ok i guess if you spend enough you can circumvent most of that so it does come down to cost, but not just because the bigger pump costs more.

Sent from my HTCONE using Tapatalk

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OldBoy

Nicely put, but I wonder to which extent it would heat up the fuel to have an over sized pump (I'm talking maybe twice as big as stock)? You could use 2 smaller pumps and stage them with the car's RPM/engine load to bypass the extra pumped fuel problems but it would come down to cost again.

1slow370

well the heat is a factor but i suspect it's mainly due to the amperage a larger motor consumes, a 255 for instance can draw 2-3 times the amperage the stock pump does, that is why it should be rewired with its own relay and larger guage wiring, 15-18 amps constant is quite a lot of power, then start talking about running two of them and you are looking at over 25 more amps of constant draw the car now has to put up with and this isn't a sound system, we are talking all the time constant draw. My old suzuki swift had a 40amp alternator, it would barely be able to keep up with just those pumps.

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Nissan370

i have my 340lph pump wired to the battery with larger gauge wiring
so i get the return stage 0 kit that should be a good starting point.

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370z vsr motorsports single turbo/built motor 9.1cr 525rwhp/450rwtq @ 10.5psi (stock maf maxed out)