I need to set fuel pressure on my Fuelab regulator. I just created my own custom hanger, feed, and return system. I am wondering about base pressure and what It should be. I pulled this from Supraforums:

I do know to have the vacuum disconnected when setting. However I don't know if I should stay at GE specs, or move to GTE specs now that I am NA-T and on GTE spec pistons etc. Not to mention I don't even know what the GE VVTi's spec really is or if it is different. Anyone with fuel system experience know what I should set pressure to when going NA-T and a return style fuel system?

If it matters I am running a 525lph pump, 8an feed/rail, and 6an return.

 

My thoughts are that right now my AEM Infinity ECU is tuned for what the car was at before the engine blew, which is factory pressures. I did not have a return system at that point and was running the in tank regulator. So for now I should set it to factory pressure correct? I need to get things broken in good before moving forward with my project, so I want to drive the car with things as they are now safely and take some time to break things in and change fluids again etc. I have a totally rebuilt Engine, Transmission, and Diff/LSD to brake in and take care of.

So what I really need is confirmation on what my base fuel pressure should be. And if anyone knows the actual GE-VVTi factory specs for sure. I feel like most information I find online is from the non-vvti engines and may be different.

 

Having exact stock specification fuel pressure will not matter for you. On a 100% stock car you will have a certain AFR at WOT, which is the result of the ECU commanding the injectors to open and close with a very specific pulse width. If fuel pressure is off on a 100% stock, the AFR will no longer be what the manufacturer designed because the injectors will start spraying more or less fuel at the same pulse width, because of the higher or lower pressure in the fuel rail. Hence maintaining the specified fuel pressure is important in this case.

You have a custom fuel system and I am assuming you will also have a way of electronically tuning the fuel delivery (standalone/piggyback ECU or something like that). So all you need to do is set your fuel pressure to a "normal" value and tune the car with that pressure. After tuning periodically verify the pressure hasn't changed, since otherwise your whole tune will be off. I would suggest setting the fuel pressure to whatever pressure your injector manufacturer has specified their flow rate at.

Edit: I only saw your first post when writing this reply. If you are not changing your tune right now you will need to set pressure as close as possible as to what the pressure was when the car got tuned. However since you switched from return-less to return style does that mean you also switched from a fuel system where pressure was not vacuum/boost referenced to one where it is now? If so, your effective fuel pressure is going to be off in any case except when you are exactly at 0 zero vacuum/boost. Best to monitor your AFR's until getting it retuned then, and adjust fuel pressure to a value that produces safe AFR's.

 

Thanks for the response. I guess I will just need to set it to as close to factory as I can because that its what it is currently tuned on. But I've heard conflicting information on what base pressure is at idle. ​​​​​​I think the engine normally runs at 42.5psi. But that's not what you'd set the pressure to at idle. Like 32 or something like that.

 

This makes sense. So the engine likes to run at 42 psi, seems like a pretty normal and believable value to me. At idle there is a vacuum in the intake manifold, could definitely be around -10 psi. So the resulting amount of fuel pressure needed in the rail will be 32 psi to keep real operating psi at 42 (total pressure differential between +32 and -10 psi). This means either set the pressure to 42 without the vacuum reference hose connected, or to 32 with the hose connected. It will result in the same.

 

Got it, I did a bit of research and will be setting it to 43.5 with the vacuum disconnected which is the actual oem pressure spec. I may or may not have to plan to set base pressure a little higher when I go to re-tune with my 1150cc injectors so they run around 80% dc. If my turbo can support my goals, the injectors should produce 1150 at 56psi under boost. And since pressure tends to bring the actual cc up, I guess the more boost, the more they will be.. But thats more fun to figure out in the future. Apparently they produce 925cc at 43.5psi. But for now I'm running 8psi boost on my 550cc set. Will be looking into it more when the time comes.

These are what I have for the near future. Hoping they support my end goal of around 700-800whp. I think setting base fuel pressure a little higher will make them sufficient for a 80%dc.
https://www.driftmotion.com/Bosch-11...m-p/dm2878.htm

 

You got it, although I don't understand this part

If all is working well you will have equal total fuel pressure (and therefore flow rate) at any amount of boost.

Example with the pressure set to 43.5psi.
Vacuum: -11.5psi in the IM, this is connected to your FPR through the vacuum hose, pulling the FPR more open, letting more fuel flow back through the return line. You will see 32psi at the rail but total pressure remains 32 - (-11.5) = 43.5
Boost: let's say 12.5psi of boost, this is connected to your FPR through the vacuum hose, pushing the FPR more shut, letting less fuel flow back through the return line. You will see 56psi at the rail but total pressure remains 56 - 12.5 = 43.5

Because the injectors have to spray into whatever the pressure is in the IM. If the IM is in vacuum it will be easier to spray (the fuel gets sucked in there by the vacuum), if it's under boost it will be harder (the fuel gets pushed back by the boost pressure). That's why vacuum referenced FPR's exist, so the pressure at the rail can change accordingly ensuring the total pressure remains equal and within operating range.

So if you actually need the full 1150cc @ 56psi, you need to set base pressure to 56 instead of 43.5.

 

Interesting, thanks for the info man! I definitely need to research the whole theory behind fuel systems some more. I guess I was just gathering that because the injectors say they are 925 at base 43.5psi. But under boost they are 1150 at anything past 56psi. So obviously the physical cc of the injector doesn't change but in a sense it does lol.

 

Another thing while I have your brain to pick. I'm using three online fuel injector calculators to figure out my needs. RC, Fuel injector clinic, and Deatschwerks all have calculators. With the same information plugged in I get the same results from the first two, but a bit different from Deatschwerks. I went with the injectors I did because going too overkill can ruin drivability etc. According to my info, they should flow 100cc over what I need at 80% dc. Before I install these, I need as many opinions as possible if they are a good choice or not. Again, 800whp is the max power goal I'd like to be set up for on pump gas. That's 91 octane here in Cali with a booster if needed. And is my 525lph pump sufficient? From everything I've researched, it should be. I saved big money customizing my own hanger/lines and don't really want to buy a triple hanger and multiple pumps. I also have a Deatschwerks hotwire kit to install too which makes the pump run good and strong.

 

The calculators make a lot of assumptions to guesstimate what you should need, you could get different results if one calculator is more conservative than the other.

I can't help you with what exact size injectors or fuel pump you need to run, because I have no experience with the 2JZ (or even turbo cars for that matter) yet. I know the theory but that's mostly from working on other platforms. But I am planning to get an Aristo which is why I decided to already sign up here and learn about the 2gs.

There is a pretty easy and reliable way to determine if you have enough fuel pump though, but it only works during or after tuning. If you can data log your rail fuel pressure, and see it dropping in the upper RPM's where injector duty cycle is highest, you need more fuel pump. The fuel pumps job is to keep rail pressure stable at all times. If you can't log fuel pressure you can still sort of determine if your running out of pump, if you see a point where increasing injector duty cycle is no longer enriching your AFR's, that means fuel pressure must also be dropping.

 

Does anyone know if the new Walbro (Ti) 525lph pumps are dimensionally the same as the 400, 450, 485, etc? I am looking into PHR's dual/tripple pump hanger from Suprastore. They offer it with 1, 2, or 3 485's, but I already have a 525, and would like to run 2 together for my fuel needs. But if the pumps are even slightly different, I don't wan to mess with fitment issues. Like the 525 sitting slightly too deep, or shallow etc. If so, I'll obviously be fine with 2 485's. Just would rather buy 1 more 525 than 2 485s to save money.

I am concerned with my fuel needs even with the 525lph because it is rated about exactly for my power goal, but I don't want to have just barely enough fuel. I want to be overly sufficient. The 525 supports 1000hp N/A but says around 800 for turbo applications. 800 happens to be my power goal.

 

Well according to this pump test performed by RealStreet, my 525lph pump seems very capable for my power goal.
https://www.realstreetperformance.co...mance/#results

They give the flow they got at many different pressures and the estimated horsepower they can support. I would obviously like to save a load of money by using the pump I have and the hanger I put so much effort into customizing. I may just be flushing $1,200 down the drain if I buy a dual hanger with pumps, and wiring harness etc. for more flow that I don't even need. Still undecided at this point though.

 

Tough decision. I mean it doesn't hurt to run what you have until you find otherwise. Wire you up a fuel pressure sensor if you don't already have one, and connect it to your AEM. Move up in slow increments. For example, if you're targeting a 11.0 AFR at full boost / RPM, and you're at 18psi and hitting target and you turn up to 20 psi, you're not likely to go dangerously-lean. If you're running out of pump, you'll see a leaner AFR (you'll notice it's missing target) and this should coincide with a reduced fuel rail pressure.

I recently installed a fuel pressure sensor myself for this exact reason. I'm on e85 and my Aeromotive 340lph pump is out of fuel at anything over about 15 psi on e85 (about e55-60). But it will easily handle 18psi+ on pump gas volume. Both the wideband and the fuel pressure sensor together tell this story. These sensors make logging and life much easier.

...now off to buy that 3-pump hanger myself. Ugh...

 

Thanks for the info, ya for e85 you definitely need more pump. You might be good with a single 525 though. Whats your goal for hp? It's good for 700ish hp on e85 at least. Pain in the but to custom the hanger for it, but way cheaper.

 

You know how it is... always assuming a lower HP number is good enough, and then you reach it and you're like... "I need more." Well I figured the 340lph would be enough to get me to a limit on this stock transmission and be useful while I save up and determine the route on the transmission. But in reality, this transmission is stouter than I gave it credit for. So what's my power goal? I don't have a number in mind, but in line with what the 1000cc injectors can support for now. Probably in the 600rwhp range. So you may be right, the single 525 might take care of me for today, but I'd feel a lot more comfortable with a couple 450's for current comfort and future growth.