Will I Need An Aftermarket Fuel Pressure Regulator?

[Crazy Xav]

Hey guys just a quick question im sure someone will know straight up.

did a search on when to upgrade FPR, the anwser was 'Never if you have the right injectors'

What I want to know, do I have the right size for my application?

Mods are as follow.

Standard RB25

Hypergear ATR43 turbo

top mount manifold, ext wastegate

front facing plenum

top feed fuel rail

Denso 850cc injectors

Wolf 3D V4 is the brain.

will i need an adjustble FPR? or will just running the lines from my standard reg/filter do the trick?

Power goal is around 270kw

Thanks

[Hanaldo]

Stock will be fine mate. I was making around the same power with 650cc injectors and stock reg

[Crazy Xav]

Thanks mate.

[femno]

Not if youre running an aftermarket fuel rail it wont be. Mainly due to the fact that the stock reg is fitted to the factory rail and it wont simply 'bolt on'.

In which case you would require an aftermarket reg.

[Moodles2]

GTR injectors (444cc) support 280kw close to max duty cycle of 100%. 850cc you have plenty of headroom, you could easily run E85 at that power level and still have headroom. Adjustable FPR will be a waste of money.

[Hanaldo]

Not if youre running an aftermarket fuel rail it wont be. Mainly due to the fact that the stock reg is fitted to the factory rail and it wont simply 'bolt on'.

In which case you would require an aftermarket reg.

Ah, didn't even see that one

[AngryRB]

stao runs 850's with ethanol and getting upto and over 300kw's , correct me if im wrong..

if you have a stock rail with the 850's then no need for aftermarket reg, i went after market cause of the top feed rail.

Edited September 4, 2012 by SliverS2

[Stock e-Tune]

Hey guys just a quick question im sure someone will know straight up.

did a search on when to upgrade FPR, the anwser was 'Never if you have the right injectors'

What I want to know, do I have the right size for my application?

Mods are as follow.

Standard RB25

Hypergear ATR43 turbo

top mount manifold, ext wastegate

front facing plenum

top feed fuel rail

Denso 850cc injectors

Wolf 3D V4 is the brain.

will i need an adjustble FPR? or will just running the lines from my standard reg/filter do the trick?

Power goal is around 270kw

Thanks

I think the comment "never if you have the right injectors" is misguided somewhat regarding regulator.

a few reasons you may install an adjustable fpr would be:

1. when you increase boost, need to ensure f/pressure is not going to exceed HP f/pumps supply (pressure vs volume)

2. if you change camshaft, often less vaccum causes from larger cam profiles cause high f/pressure

3. as forementioned, if the aftermarket rail doesn't have a fitting for stock FPR. (should be a no brainer for the tuner)

4. if large injectors are used and have poor low pulse width control.

5. if trying to improve fuel economy. (often best to run higher pressure where possible)

6. different fuels being used, eg, methanol/e85/m85/e10 etc. high fuel pressure with higher content of alcohol.

if you want to run e85, other fuel system consideratinos must be made first, fuel tank, fuel lines, fuel pump, compatible fuel regulator etc.

but thats another day.

The 850cc's are fine for a little while longer,

this time depends on the duty cycle at the highest rpm the engine is designed to reach and

of course if the fuel pump can supply the volume at that higher pressure (base pres + boost pres).

[Crazy Xav]

Looks like ill be purchasing an aftermarket one as i will need speedflow type fittings for the ends of the fuel rail.

Seems like obviously to set up would be.

fuel filter hose to fuel reg, fuel reg to fuel rail & other end of fuel rail to the damper which is on the side of the engine bay?

[femno]

Yep. Like I said you cant connect a standard reg to an aftermarket reg. Plenty seemed to miss that.

Youll need to connect the fuel filter hose to the rail, then from the rail to the 'in' port of the reg, then the 'out' port of the reg goes back to tank. A reg works by restricting the return from the rail.

[GTSBoy]

Yep. Like I said you cant connect a standard reg to an aftermarket reg. Plenty seemed to miss that. Youll need to connect the fuel filter hose to the rail, then from the rail to the 'in' port of the reg, then the 'out' port of the reg goes back to tank. A reg works by restricting the return from the rail.

READ the above and understand it. Because he is right.

On the other hand, many cars these days do run a dead head fuel rail. The reg is actually located at the back of the car and returns fuel direct to the tank. The fuel that goes forward is all destined to go to the rail and then into the engine - no return. There are concerns with fuel heating and so on (which is why flow through rail return systems were invented in the first place). The concerns are that if you have fuel sitting in the rail while car idles hot at the lights on a hot day (for example) then you might boil the fuel in the rail and cause havoc for yourself. This probably won't happen whilst running because the 3 bar pressure will tend to help stop it from boiling. But it can certainly boil in the rail after parking the car in the same hot hot conditions. This could stop you from being able to start it. A flow through rail will at least be able to purge the vapour out as soon as the fuel pump is switched on, and so you can start them. The advent of dead head systems means that the concerns over boiling were either unfounded or they have found ways around it.

What this means is that you could actually run the supply hose up to a T piece on the inlet of the reg and run the other leg of the T to the fuel rail. Priming the rail from empty might be a bit of a pain in the arse, but the reg would otherwise work as advertised. It would close down to restrict flow to the return to maintain pressure in the rail, and open up to let it go when demand at the engine was low. There might be usability problems with it, but it will still work.

[discopotato03]

I reckon std replacement or a std replacement one for something that uses rubber fuel hose both sides . I cant see the point throwing money at pretty aluminium screw fittings for a road car . Its not like its being ripped apart in the pits all the time .

Someone does aftermarket adjustable FPRs for Nissans and I think the SR ? one uses hose barbs both sides . Brass barb from you rail to something like this would be cheaper more stealthy and work just as well .

IMO bigger injectors with a bit more pump running std fuel pressure .

A .

[discopotato03]

I now think there's a bit more to fuel pressure regs than meets the eye . Obviously the OE one is designed to suit a factory std car as in std turbo/boost/cams/injectors/fuel pump inc the high low voltage system .

From what I read in here you ending up tossing most things on say an RB25det because externals like the AFM/injectors/pump etc aren't good for much extra power - fuel flow air flow etc .

So you reaches for the bigger fuel pump and do the direct battery rewire , add larger injectors a Z32 + PFC and tune . If you don't have a wide band and gauge etc you never really know what's going on AFR wise and you take the tuners word that everything's apples .

Then you throw a wide band in and you find things the tuner couldn't get around like say that learning business with PFCs and maybe injectors that aren't as modern as current good ones . Things like mixture control at light loads and cruise aren't brilliant and you can't seem to piss off that rich spike you get when backing off from part throttle . Fuel consumption can be pretty average around town too . Recently I was into the ViPec again and tried a different approach to the cam switching and pump low/high maps (neither based purely on revs BTW) and found better cleaner running . The real surprise was finding how much easier the low/cruise mixtures were to get right by having the pump at low voltage meaning less pressure/flow for the injectors to try and work with .

Just so you know I'm running a 33GTR pump 740s and 256 Tomeis , fuel pressure reg is std . Scotty asked me recently if I was "over running" the std reg and at the time I said I didn't think so but now I think differently . Obviously those Nismo 740s aren't up with EV14s and when you're idling at about 1 ms IDC they need all the help they can get . Maybe it's better accuracy that makes EV14s a tuners best friend because they don't have to screw around with all kinds of things to make older injectors play nice .

The point of all this , IMO anyway , is that once you fit higher capacity fuel pumps and direct wire them the std FPR probably won't cope too well if and may struggle to regulate fuel pressure properly at short injector pulse widths . I think Scotty said somewhere that the std reg has a quite small bypass passage so with a big pump running at full voltage it can't open up enough to prevent the pressure rising under those conditions . It probably won't be an issue with the revs up a bit and a some engine load and that's all some people care about . So , with big pump full voltage the only simple way to make the fuel system run in regulation (base pressure + manifold pressure) is to use an aftermarket fuel pressure reg that can bypass more fuel than a std one can .

If you can find a way to keep the high low voltage system that will help but getting the std wiring to cope with current draws like that E85 Walbro can drag at times won't work .

A .

Oh and BTW EFI Hardware is doing this nifty gadget to adapt a std FPR to aftermarket billet fuel rails . Handy .

http://www.efihardware.com/image/2358/regulator-and-adapter-alloy-fuel-rail-end-8-o-ring-port-to-Nissan-regulator_2358

Edited September 3, 2013 by discopotato03

[Worngendofspanner]

Hey all, know this is an old thread but didn't want to start a new one unnecessarily. I've got an rb25det neo that runs richer than a Bavarian chocolate cake after a 4 course, specs are:

Stock turbo

Uprated intercooler

Uprated fuel pump

Stock rail and intake

3" turbo back exhaust

Just wondering if the rich condition could be because of an undersized return line. Cheers in advance.

[GTSBoy]

Nope.  Nothing to do with the fuel system.  It will be in the control system.  AFM or O2 sensor.

[KiwiRS4T]

Or of you're keen get a Nistune chip and tune it.

[Worngendofspanner]

Thanks, glad I didn't waste my money on that one?