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Upgrading Fuel Pump

DaveB

By DaveB,
in Engines & Forced Induction

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DaveB Mentor

DaveB

Posted
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Hi,

I've searched for a post about this topic but I can't find a straight answer. I have a (hopefully) fairly straightforward question; I have a stock RB25DET NEO (S2 stagea) with stock fuel pump and FPR.

Is it possible to upgrade the in-tank pump with a walbro GSS-342 (255L/hr) pump and keep the stock fuel pressure regulator? Or will it need adjustment to maintain the stock pressure?

I got a tomei adjustable FPR at the same time as the pump, but without a fuel pressure guage, I don't know what the base fuel pressure will be so I'm planning on swapping the pump myself before my tuning day, to save install cost, and just get them to install the adjustable FPR. Would this work?

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discopotato03 Grand Master

discopotato03

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Hi Dave , I believe the theory is that if the pump and injectors are up to adequately feeding the engine the std FPR should be fine . It seems the reason people go with adjustable FPR's is because they are running out of injector capacity and the only way to squeeze a litttle more through is raise the fuel rail pressure .

Roller cell EFI fuel pumps are like most fluid pumps - as the output pressure rises the volume falls off so if you can keep the fuel system in "regulation" the rail pressure will be inlet manifold pressure plus the diaphragm spring pressure ie 35-38 pounds .

There is no reason why you can't use the Nismo FPR set to the std static pressure - at least being new it should be a known quantity .

People have mixed opinions over those Walbro 255 l/hr pumps , they are said to be popular because of their price but one issue keeps being brought up . People here and in the US who push them sometimes find that they suffer a large fuel pressure drop when use in high manifold pressure (boost) apps , they pump adequately till the pressure goes up and then the volume can be inadequate . I haven't used them myself , it was suggested to me that the relivant model GTR pumps work well ie R33GTR pump in R33GTS25T which is what I have .

I figure that with Nismo 740cc injectors I should never need more that the factory regulators pressure head to make good road car power .

Cheers A .

DaveB Mentor

DaveB

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  • Author
Posted (edited)
Hi Dave , I believe the theory is that if the pump and injectors are up to adequately feeding the engine the std FPR should be fine . It seems the reason people go with adjustable FPR's is because they are running out of injector capacity and the only way to squeeze a litttle more through is raise the fuel rail pressure .

Roller cell EFI fuel pumps are like most fluid pumps - as the output pressure rises the volume falls off so if you can keep the fuel system in "regulation" the rail pressure will be inlet manifold pressure plus the diaphragm spring pressure ie 35-38 pounds .

There is no reason why you can't use the Nismo FPR set to the std static pressure - at least being new it should be a known quantity .

People have mixed opinions over those Walbro 255 l/hr pumps , they are said to be popular because of their price but one issue keeps being brought up . People here and in the US who push them sometimes find that they suffer a large fuel pressure drop when use in high manifold pressure (boost) apps , they pump adequately till the pressure goes up and then the volume can be inadequate . I haven't used them myself , it was suggested to me that the relivant model GTR pumps work well ie R33GTR pump in R33GTS25T which is what I have .

I figure that with Nismo 740cc injectors I should never need more that the factory regulators pressure head to make good road car power .

Cheers A .

Thanks guys.

I have stock injectors, so the FPR is for when I get my dyno tune (installing gcg high-flow neo turbo, split front/dump, high-flow cat and soon cat-back exhaust, so I hope to be ready to push the injectors past the ~85% duty cycle which is considered "safe"). I hadn't considered flow though. I'm not up with the pressure / flow stuff, but if the pressure is set the same, will the flow be equal? I have just read the instructions for installing the pump and it says to "road test" the car after installing the pump, so I guess it expects factory FPR will suit.

discopotato03 - by:

There is no reason why you can't use the Nismo FPR set to the std static pressure - at least being new it should be a known quantity

...do you mean that the FPR comes set at a certain pressure? Do you know what it is, or is it safer to set it up with a fuel pressure guage (which, if I was smart, I would just try to borrow from somewhere and set the new FPR up to the factory pressure, and save on the cost of FPR installation as well).

I guess the main reason we all do this FPR replacement is of course it's a ~$150 option to increase injector flow by like 10-20%(?) as opposed to the $750 new injectors option to increase flow by 50-100%+. ie. cheaper. And I don't want/need more than the factory injector capacity really (ie. it's not the only limiting factor) - somewhere around 230-240kW - because not much above that I have read of stageas breaking half-shafts, and by about 250-300rwkw the flex plate in the auto is a weak link.

Edited by DaveB
R31Nismoid Grand Master

R31Nismoid

Posted
Posted
In my case new fuel pump bumped the fuel pressure up, more than the manual states. I had to install adjustable FRP to turn the pressure down a bit to a factor 2.5bar. So factory frp doesn't work properly or whats the go ?

yours could well have been on the way out

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