AdrenalineS14

Hey all ive been doing some research on this matter about what settings the fuel pressure should be at, I do understand with a stock sr20det its set at 3 bar(43.5psi) with the vacuum off on the stock regulator and ive also seen people talk about running it at 4 bar... anyways i would like to know what mine should be set, i have the nismo fpr, aftermarket fuel pump, and 810cc injectors, motor is built and will be getting a tune here soon, is this something i should let the tuner know so he could mess with it, but really i want to know as well lol. im shooting for just over 300whp and wanting it to run a tad bit rich to be on the safe side... im just wondering what is best, running it on 3bar, 4bar??? would like to hear what others are running with a similar setup:

Head:
BC 264 cams with stock cam gears
BC springs and retainers
stock valves
freddy intake mani
silk road exhaust mani

Block:
86.5mm Mahle pistons
eagle rods
acl race bearings
power enterprise pe1420 turbo

gonna be tuned on a power fc

GroundPerformance

Leave it 3 bar and less stress to your fuel system. Most 4 bar setups are the ones running E85 that needs the additional fuel flow and better atomization. So other than that leave it at stock besides don't think the Nismo FPR are up to the task at such high static pressures or would I trust it. IMO

AdrenalineS14

Cool thanks for your input ill do that... btw what is the proper way to adjust it, is it with the vacuum hose on or off? again thanks for the help!

chituntang

Hose off

First, 4 bar setup does not stress fuel system more compare to 3 bar setup. It does stress our car more only because things were designed with 3 bar fuel pressure in mind.
Second, all gasoline engines benefit from better atomization, not just E85; and increasing fuel pressure is one of the many ways to increase fuel flow.

GroundPerformance

I'm certain were just taking about SR and 240sx in general here but now that you mention it. Injectors are now standard to be measured at 3 bar for most any new FI cars. Also, Before advising OP to up his fuel pressure 810cc is a good size injectors already and not all injectors will just take as much pressure as send to it and you will need to a decent fuel pump and fpr to support it. Not worth IMO. Besides if the OP wants to boost lets just say 25psi your fuel pressure will be around 83psi dont think i like that range.

codyace

I'm not sure I understand you here?

4 bar most certainly does stress anything more than a 3 bar fuel setup.
- Injectors rated at 3 bar FPR will run hotter/harder at 4 bar
- Fuel pumps will need to pump much more fuel, causing stress on stock stuff and or requiring an aftermarket pump that can support higher pressure fuel (remember, 15 lbs on a 3 bar setup require a pump that can support 58.5 psi of fuel...if it's 15 lbs on a 4 bar setup, it needs to support 73 psi etc etc

This applies across the board.

While increasing pressure does increase flow you need to remember what the setup is tuned on/for. Regardless of a setup, when it's tuned on XX psi, it needs to stay there. 3 or 4 bar psi base makes no difference in that regard, as if you want to tune your car lets say on 50psi, that is where it's going to be set at, but you need to remember that the 72lb injector is now really 'larger' in base size (generic terms to make it easy for the O/P). As before, if the car is tuned at a specific fuel pressure, that is where it needs to be forever, as changing the fuel pressure base will change the tune.

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chituntang

From what I learned, newer cars run higher fuel pressure. So, if the stuff you use are designed for 4 bar system, it will not stress more/less than 3 bar system. Of course, most of the aftermarket fuel system parts for the s chassis are designed to run with our stock 3 bar system. Therefore, making them run at 4 bar will stress them, especially with the most common cheapass Walbro fuel pump and Nismo FPR fuel system upgrade.

I do have questions for you guys now: How much more stress will the injector has from running a 4 bar system, compared to a 3 bar system? And does better atomization not count as a reason to run 4 bar system?

codyace

Obviously if a car is designed to run a specific pressure, it's fine. I'm not arguing on the technical aspect of things, more on the specific side of it (in this case the 240sx). No reason to argue things globally, as we could get into mechanical systems and really get funky.

Again, my comments are in relation to the 240sx, and nothing more.


What S chassis specific stuff (for fuel) do we really have? Nothing that couldn't support 4 bar (FPR and fuel rails are totally fine, the stock lines are as well). What I'm talking about are using things above and beyond their rating. Stock fuel setup should never be driven beyond 3 bar IMO.

Now with aftermarket stuff, there is no doubt that running anything at a higher pressure is going to stress them more than a lower one, that's my only point; don't read to far into it. Lower pressure = lower workload = longevity

And unsure where you get the 'cheapass' Walbro idea from? A 255HP pump is plenty, and more than sufficient. However back to our comments in regard to pressure, anyone running big boy boost, or higher than OE fuel pressure should invest in the 'high pressure' 255, not the traditional setup. (lets say over 14 psi)


I'm not sure why you are hung up on this fuel atomization thing...

How much stress is hard to measure, but read my comments above; running the system at a lower base fuel pressure will decrease wear.

Cliffs: You need more fuel, it's safer to run a larger injector at a shorter duty cycle or less fuel pressure than it is to run a smaller injector at longer duty cycle or more pressure

__________________

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Quest Alternator Conversions for SR20! Check my Group Buy!

Tired of lousy internal gates? Go external wastegate with one of my manifolds, Check out my group buy

AdrenalineS14

oh boy, now to make a decision lol... ill check back and see if others will hop on this and share thoughts about all this

chituntang

OP, listen to Codyace. He's a knowledgeable guy in our community, and I always seek answers from him, including this one.