Aftermarket Fuel Rails

[Sydneykid]

From the number of PM's I get on this subject I figured it was time for a discussion on the fuel rails and fuel pressure regulators.

Let me start off with 2 pictures, the first is the Gibson R32GTR;

Notice that it has the standard fuel rail with a dash fitting welded into the end. It also uses a mechanical fuel pump, running off the inlet camshaft. The reason for this was the lack of really big electric fuel pumps (volume and pressure). This was necessary because there were no high volume injectors around like there are today, so to get the flow they used higher pressure. Hence the need for the dash fittings, the standard hoses and clamps would not have handled the fuel pressure. But they obviously believed that the standard fuel rail was sufficient for the task.

The second picture is the Mines R34GTR;

Notice that it also has the standard fuel rail, obviously Mines (like the Gibson Team) believed that the standard fuel rail was sufficient for the task. It also has an adjustable fuel pressure regulator (Nismo style) fitted to the end of the standard rail. It is reported to run 600 cc injectors to support its 600 bhp, so the adjustable fuel pressure regulator must only be used to give a little head room. This means not much more than standard fuel pressure, which is supported by the use of standard (looking) fuel hoses and clamps.

What do these picture tell me;

1. The standard fuel rail must be pretty good for 600 to 650 bhp.

2. The local workshops who say that the adjustable fuel pressure regulators (Nismo style) fitted to the end of the standard rail are not reliable and/or stable in their pressure obviously know more than Mines do (I don’t think so Tim).

3. Upgrading hoses and clamps (to dash/screw on fittings) is not necessary when standard or close to standard fuel pressure is being used. Simply put, if you have the correct size injectors for the engine’s bhp then standard hoses (good condition of course) and clamps are OK because you are running standard fuel pressure.

4. Both of these teams have sufficient funds and technical skill to change whatever they want. Hence it is not unreasonable to say that if the components used where even CLOSE to their limit, they would have upgraded them.

5. Assuming a 10% headroom, that would mean ~700 bhp is a reasonable limit for the standard fuel rail, single fuel feed point, Nismo style fuel pressure regulator and standard hoses and clamps (in good condition) if the injectors are sized correctly.

The bottom line I wouldn’t be changing the standard fuel rail unless your power target is over 700 bhp.

For the “rice” lovers, the standard rail is cad plated stainless steel, so they polish up very nicely.

Cheers

PS; Bet the retailers don’t want to hear that!

Edited April 5, 2006 by Sydneykid

[Bass Junky]

SK

What are those photos of the heads all about?

[Sydneykid]

SK

What are those photos of the heads all about?

Work in progress on my own engine.

cheers

[R31Nismoid]

Couldnt agree more.

I made over 300rwkw for a while with the stock fuel rail, and even the stock fuel reg

I too believe a lot of stock or near stock stuff is all most people will ever need. So many places will try tell you otherwise to make some more $$$ from the unaware customer

[N1GTR]

This thread came at the perfect time for me

Cheers SK!!!

[Black_R33]

From a GTST perspective, 3 years ago I upgraded my fuel rail because my rb25/30 conversion needed more fuel for our power level than the standard r33 gtst injectors could supply. I could not find a cheap side feed injector upgrade option at the time! A Custom rail and cheap 550cc rx7 top feed did the job in my case.

[CruiseLiner]

hey i tryed to polish my stock fuel rail and it came up nice and went really shitty yellow after a while, didnt look good at all for the rice look

good info though, ive already bought mine but it cant do any harm now can it

[Col-GTSX]

I run a standard fuel rail and just a pfr and bump up the pressure slightlly and this has always worked for me...

I didnt look into aftermarket rails til the last couple of weeks and found that pleniums like the greddy are made to take the standard rail. So aftermarket as you said is really on nessary over 700hp...

[paulr33]

in the case of the rb25 neo where you are limited to nismo 480cc

is the only next choice if you need more fuel is to change the rail to top feed or whatever is the more common one and crank in any injectors to suit ?

[Denver]

The bottom line I wouldn’t be changing the standard fuel rail unless your power target is over 700 bhp.

For the “rice” lovers, the standard rail is cad plated stainless steel, so they polish up very nicely.

Cheers

PS; Bet the retailers don’t want to hear that!

This is pretty much the conclusion i came too, but ill be adding dash fittings to it, and ive got a sard reg to go with it, main reason im going dash fittings, is its a race car, i want it all to be reliable, dash fittings also look a hell of a lot cleaner than lengths of rubber hose, and a lot easier to remove than trying to break the seal a rubber hose forms to the hardpipe when it comes to removing the motor if need be..

now if only they wern't so stupidly expensive...

[Sydneykid]

Good feedback guys, thanks.

My own fuel rail is a combination of the Gibson and Mines. I have used a Nismo bolt on FPR in the standard location at the front. I cut off the standard fuel pipework and fitted a dash fitting into the rear of the rail. It is simply threaded into the rear of the rail where I cut off the standard pipework.

I will post up some pictures shortly.

cheers

PS; on the RB25DET Neo injectors question....when we had the R34GTT I used the Nismo 480 cc injectors. They had no problems with 315 rwkw with a slight upgrade in fuel pressure (couple of pounds). I figured that was plenty for the standard internals.

Edited April 6, 2006 by Sydneykid

[dangerous_daveo]

So can I ask. For us people running standard turbos with just boost etc. Is an aftermarket fuel pump worth it, assuming stock fuel pressure. Then if its stock turbo etc and fuel reg is it needed?

I already have one as it came with the car so it doesnt worry me, just interested to know.

[Roy]

But they look ghey I thought about HPC coating the external of mine and running braided lines to welded dash fittings. My feul rail is often too hot to touch, thought the velocity of fuel through the rail may make it a waste of time...but still look better.

Whilst the real world experience suggests that the std rail works ok...i have often wondered whats entailed when checking the spray pattern of an injector?

Why cant someone simply use the injector in the rail rather then the test rig to conduct the spray test??? It woudl be interested to see if they all spray the same?

[carl h]

garry, what do you think about modifying the std rail to be dual feed (feed on opposing ends) for more even fuel flow.

i had considered doing this to my rail to help prevent leanout.

[BBGTR]

garry, what do you think about modifying the std rail to be dual feed (feed on opposing ends) for more even fuel flow.

i had considered doing this to my rail to help prevent leanout.

Sorry to hijack,

I would have thought that a correctly rated fuel pump before the pressure regulator and correct pressure after the regulator would be more important than flow. Flow is more or less function of these two things.

Having one or two entry points would make no difference.

I too have an R32 GT-R with 310 RWKW with a standard fuel rail and 800cc Green Sard Injectors.

OEM equipment is so durable when used within it's intended parameters that I wouldn't bother considering much else, it's a waste of money in my opinion.

Regards

Andrew

[Roy]

Sorry to hijack,

I would have thought that a correctly rated fuel pump before the pressure regulator and correct pressure after the regulator would be more important than flow. Flow is more or less function of these two things.

I hear what you are both saying...but i think what Carl is getting at the old blow a fluid in an end of pipe that has equally space openings adjacent to the flow, and the earlier openings will naturally flow less then the latter.

Supplies at either end will get rid of this.

Perhaps because the injectors act as a valve that opens and closes whereby switching the flow that it doesnt make sense to model it as per the above example...hence why i would be curious to see the spray patterns of the injectors mounted in a fuel rail?!?!?!

[BBGTR]

I hear what you are both saying...but i think what Carl is getting at the old blow a fluid in an end of pipe that has equally space openings adjacent to the flow, and the earlier openings will naturally flow less then the latter.

Supplies at either end will get rid of this.

Perhaps because the injectors act as a valve that opens and closes whereby switching the flow that it doesnt make sense to model it as per the above example...hence why i would be curious to see the spray patterns of the injectors mounted in a fuel rail?!?!?!

I always wondered about that - especially with say the GT-R plenum design.

For the sake of the discussion, wouldn't the fuel reg provide a constant pressure environment by continually adjusting for pressure variations generated by injector openings? With 40+ lb's (excluding manifold pressure reference changes) of fuel pressure in the rail I wouldn't have though that the first couple of injectors would ever be starved.

Regards

Andrew

Edited April 6, 2006 by BBGTR

[Roy]

????????????????????????????

The manifold has valves opening and closing, i once modelled an inlet manifold using Computational Fluid Dynamics software...it took a looong time to model and even then it was kinda crude, but what goes on inside a manifold cant be modelled by blowing a bit of water through a pipe...so if Nissan made the manifold the way they did...then for good reason.

Here is the thing, the fuel reg is on the front of the fuel rail. So someone correct me if im wrong, its an open control system and has no means of feedback. It does its thing with the upstream and downstream pressures and they are what they are.

Having a think about it i can think of reason why the higher pressure would help and hurt equitable flow...

I think the fact that the injectors mean its not a steady flow but a pulsed on/off ensures that it is far less an issue and all the theory in the world is wasted...

But i would still love to see the cc and spray pattern of an injector testing whilst in the rail being switched on/off

[BezerkR32]

This is the only reason i would sugest using aftermarket rail also, easier to find injectors to suit application.

with GTR rails its not a issue.

From a GTST perspective, 3 years ago I upgraded my fuel rail because my rb25/30 conversion needed more fuel for our power level than the standard r33 gtst injectors could supply. I could not find a cheap side feed injector upgrade option at the time! A Custom rail and cheap 550cc rx7 top feed did the job in my case.

[BezerkR32]

you can see this in an off car efi cleaner. all injectors behave different, some injectors spray pattern suffer from over pressure, others dont. keep in mind that all factory parts are designed to operate inside set parrameters, when you start doubling boost pressure, you automatically double yor fuel pressure, which then starts to ask the question of the fuel pump. fuel is probably the most important aspect of a turbo car, and one you should not cut corners with. modify your system to suit your application. Upgrading fuel pump is a no brainer as most peoples pumps would be at least 10 years old anyway. Upgrade injectors if needed.

You will kow on the dyno if your at 90% duty, you have to upgrade. then the rail is sometimes necessary to be replaced depending on your style rail to suit new injectors, although you can now get high flow side feeds. after market reg is sometimes necessary with aftermarket rail as they do not incorporate the standard reg. Depending on the extent of your engine modifications, you should modify fuel system to suit.

everyones needs will be different, so posting that you do need this and dont need that is incorrect.

????????????????????????????

The manifold has valves opening and closing, i once modelled an inlet manifold using Computational Fluid Dynamics software...it took a looong time to model and even then it was kinda crude, but what goes on inside a manifold cant be modelled by blowing a bit of water through a pipe...so if Nissan made the manifold the way they did...then for good reason.

Here is the thing, the fuel reg is on the front of the fuel rail. So someone correct me if im wrong, its an open control system and has no means of feedback. It does its thing with the upstream and downstream pressures and they are what they are.

Having a think about it i can think of reason why the higher pressure would help and hurt equitable flow...

I think the fact that the injectors mean its not a steady flow but a pulsed on/off ensures that it is far less an issue and all the theory in the world is wasted...

But i would still love to see the cc and spray pattern of an injector testing whilst in the rail being switched on/off