600+ and fuel setup
 

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

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.

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

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.

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

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.

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.

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.

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

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 :)

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:rofl2:

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??

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

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.

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.

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.

Yes with a 950cc injector, a 340lph pump, and a stage 0 kit, you shouldn't have any trouble achieving in the 500s. There are not enough samples of built motor results yet to give extremely accurate estimates. However, its a cost effective system that is easily upgraded to our larger stage kits down the road if you run into any pressure drop issues.

Hahaha, yeah reminds me my '90 Civic Cx base model with the 60 amps alternator, could barely run every electrical accessories at the same time.

I agree it would pull a lot of power from the alternator just to keep up, but really, thats the price to pay to pump more fuel into the engine, there's just no getting around it. Plus, most newer cars have very large alternators to keep up with all the powered accessories.

That being said, I think it would be interesting to use a twin pump setup for high HP engines. I'll elaborate a bit more on what I meant by 2-stage. Imagine having 2 pumps each hooked up on a separate relay. First one could be an OEM sized pump that's on all the time like a regular fuel pump. The second one on the other hand, would be a high output one and could be wired to a relay which would be energized by a fuel pressure sensor on the fuel rails similar to an oil pressure sensor but set for 50 PSI. So essentially, the second and bigger fuel pump would only come on if the pressure was dropping below 50 PSI. This way, when your just cruising around, your not drawing 25+amps all the time and moving massive amounts of fuel heating it up, you'd only pump it when its really needed. Add a little timer on the relay to keep the pump from cycling ON-OFF for nothing and you're good to go.

One of OEM's reasons for keeping the pumps small are very strict EVAP emissions regulations. This is also one of the several reasons for a factory return-less fuel system.

What you mention about a twin pump setup.. that is very close to what is already being done. The Nissan GT-R uses 2 pumps from the factory in a comparable configuration.

We offer a twin fuel pump unit to our customers. We always recommend that people wire it to be staged, where one 255lph pump is on full time, and the second pump is energized at higher engine load.

It isnt a good idea to wait until fuel pressure drops to engage the secondary pump.

Based on your post, there is a product series I believe you may find interesting. Fuelab has a line called "Prodigy". The prodigy pump is controlled by their fuel pressure regulator. The regulator monitors volume of return fuel. It has a target volume it tries to meet, and it will increase or decrease pump speed to achieve as close to that return volume as within its range. This means the system is providing the "just right" amount of fuel at all times, proactively, before there is any pressure drop or increase.

We have been waiting to see how the Prodigy line up proves itself for reliability before designing any fuel system kits that depend on it.

Very interesting about the EVAP emissions regulations, didn't think of that one. I guess the more you move fuel, the more vapors will be created in the gas tank, but I don't see why a return-less system might be better tho?

Haha, just as I thought, I knew they were smarter people than me that thought about that one way before I did.

Well if OEM specs are 52+/- PSI @ idle on our Z, I thought it wouldn't be that bad if it was dropping to 50 before turning on the second one. I'm sure it drops more than that on most guys' FI setup running in the high 500's whp?

That being said I agree it wouldn't be the most elegant way of doing it. The electronic fuel pressure regulator from Fuelab you're talking about would be a much more efficient way of doing it.

Thank you for that very interesting info good sir :tiphat:

Odds are, I'll be contacting you around next spring. I'm contemplating doing a return system conversion on my Z before I get tuned next year.

A return line generates a small, but measurable amount of evaporative emissions since the fuel traveling through the line will permeate through the line over time. Therefore, it would require more expensive material that prevents permeation known as SAE J30R7 rated hose. Even then, the longer the line, the more surface area that the fuel can permeate through. Therefore, it is ultimately less expensive to use a returnless fuel system to keep evaporative emissions low enough to pass EPA and CARB mandates. When it comes to OEM's, saving a few pennies per car translates to big savings over tens of thousands of cars.

Small but measurable amount of evaporative emissions??:bowrofl: Ch*@$, they really are going ape sh!t with all those emission standards. I wasn't even aware fuel lines were permeable before today... I guess you learn something new everyday.

Typical fuel hose from the 90s would permeate but I don't believe the modern nylon and Teflon hoses they use will permeate. I at least know that if it does permeate, it's a small fraction. But I cannot say with certainty that it doesn't at all. I believe that the evap of a return system has more to do with the heating of the fuel that is effectively cooling the rails and bringing the heat to the tank. Then again, the evap in the tank gets vented to the intake manifold eventually other than the pressure that escapes when you open the gas cap.

This forum is probably the wrong venue to get proper details on emissions systems since it's the last thing most tuners think about or study!

That's exactly why I find it funny that government regulations are giving the OEM's trouble over the extremely small permeability of the fuel hoses when you vent everything to the atmosphere by opening your gas cap. :ugh2:

That is a great point, lol! :tup:

I've just begun to research the idea of a two staged fuel pump energizing system for my CJ Motorsports twin fuel pump with a full return fuel setup.

Any recomendations? I do like the idea of a RPM based trigger

Zat

When it's an option, I would always try and use a standalone EMS' configurable output to ground a relay for this. But I understand that isn't really an option in a 370z since nobody runs a standalone EMS.

There are some secondary methods it could be done. If you were looking for an RPM based setup, there are many simple RPM window switch products available.

I believe what is most popular is to use a pressure switch that will engage the secondary pump at a specific boost pressure level. I commonly hear of Hobbs Switches being used. I believe there are also other similar types of pressure switches out there.

Be sure of one thing... use the pump that is closer to the over-tank siphon hose barb on the bottom of the twin pump as your primary pump. That is because this pump is what actually runs that siphon in our assembly. We do not "power" the venturi with return fuel like that OEM sending unit. That would cause far too many problems with the volume of return fuel a pump like that provides.

All of that about our electronic regulator is true. However, the pumps have other means of controlling the speed without an add-on such as the regulator. That electronic regulator is fairly new- it's been out about a year an a half or so. We have had only one warranty return/repair since their release. They have been working out really well for us. The regulator can also control more than one pump. We have several guys in the drag racing world that are running on straight methanol (much more flow needed). They are using a pair of our big 42402 pumps and controlling them with one regulator. With that said, you can control the pumps via other, potentially less expensive ways. The electronic regulator gives you variable speed operation. Another way to get the variable speed operation is via a PWM signal from an aftermarket ECU (some factory ECU's can do this as well, but that's pretty rare). If you can feed the signal terminal on the pump a PWM signal that's been 500hz-1500hz, it should work just fine. That would require a bit of tuning/setup unlike the plug and play regulator- but people have been doing that for years (long before we designed/released the regulator. Another option that works well would be a simple switch, RPM window switch, WOT switch (like what's used in a lot of nitrous systems), a Hobbs switch, etc. Those options would give you a simple high/low operation, rather than variable speed. Leave it on low for street driving and flip the switch for racing and things of that nature. In the case of a Hobbs switch, the pump would be in low speed mode until the Hobbs switch sees the engine come up on boost- when that happens, a signal would be sent to the pump to tell it to go into high speed mode. It goes without being said, but our pumps will work with any regulator- our standard and mini regulators, the electronic version, or any other brand out there. Our EFI pumps cannot be setup as a returnless or deadhead type system, although our carb line of pumps can (not that carb pumps are of any use to you guys here).

The pumps have a very simple wiring setup. Power and ground just like any other pump. There is a center terminal that controls the speed of the pump. If that center terminal sees ground, the pump will operated in a pre-programmed low speed mode (40%-60% flow, depending on pump model number). When that ground is taken away, the pump will operate in high speed mode.


If anyone has any tech/install questions- feel free to contact me. No sales questions please- just keep it tech related. I'm just here to help from a tech standpoint with fuel systems in general (doesn't have to be our brand).

Josh,

How about an in-tank version of the 42402? Or are we perfectly clear to submerge the existing inline model? If so, do you have a pickup filter that attaches directly to the inlet of the pump?