What Mod Next? Inj Max Out?

[letemlaf]

I have been doing a bit of reading on here to find out what the next mod i should do to my car is.

My goal is about 330rwhp with a good dose of torque

i currently have a S1 33 gtst with:

Turbo back Exhaust

Cold air box w/pod

Front mount cooler

Power FC

Walbro fuel pump

running 13psi

also with a brass clutch

I've read that alot of people have had good success with GCG high flow turbos with a fair wack power atw, but still running standard injectors. I was under the impression you can get a good 295ishrwhp with standards but anything more than that they will start maxing out.

Ive had a maximum inj duty of 97% and its only been tuned to the 270rwhp mark, could that have been a once off spike?

The last thing i want to do is have my engine go bang so i would like your advise on what my next investment should be, or if im missing anything like upgrading my coils etc.

Thanks!

[Steve]

definately do injectors next, 97% is too high, you would also be better off getting a Z32 AFM, cos your factory AFM is near its limits too.

I would recommend doing a fuel pressure reg at the same time, as aftermarket injectors are designed to run at different fuel pressure to the factory.

Factory base fuel pressure at idle is 2.55kg, aftermarket, usually 3.0kg

Having the correct base pressure will ensure that you are getting a nice spray pattern at idle, and also it will mean when you put in for example 550cc injectors, you actually have 550cc injectors, rather than 510cc

I am sure several people will now completely disagree with me

[Steve]

also, if you havent done it yet, upgrade your brake pads, being able to accellerate is great, stopping is more important

[Sydneykid]

definately do injectors next, 97% is too high, you would also be better off getting a Z32 AFM, cos your factory AFM is near its limits too.

I would recommend doing a fuel pressure reg at the same time, as aftermarket injectors are designed to run at different fuel pressure to the factory.

Factory base fuel pressure at idle is 2.55kg, aftermarket, usually 3.0kg

Having the correct base pressure will ensure that you are getting a nice spray pattern at idle, and also it will mean when you put in for example 550cc injectors, you actually have 550cc injectors, rather than 510cc

I am sure several people will now completely disagree with me

OK, he says puting his hand up, that would be me.

Aftermarket injectors (eg; Nismo) designed for use with RB25’s use the standard Nissan fuel pressure, which is 34-36 psi (2.3 to 2.5 bar). Aftermarket injectors designed for use on other engines (that may or may not require adaptors to fit RB25’s) may or may not be specified for the same fuel pressure. Their operating and flow rating are specified. BUT (there is always a but) I have not found any injectors that use different fuel pressures that will fit RB25’s.

So while you are right in theory, in the real world that is simply not the case.

Plus I defy anyone to tell the difference in spray patterns between 2.5 and 3 bar base pressure. Remember injectors in turbo engines have to have good spray patterns at absolute pressures ranging from 2.0 to 6.0 bar (plus or minus vacuum and boost). So 0.5 bar is neither here nor there as far as their spray pattern is concerned. This is not always the case in injectors intended for N/A use however. Rochesters for example, like to have their specified fuel pressure at all times and don’t handle drastic increases or decreases.

Back to the original question. With a perfect tune and an engine in perfect condition the standard injectors are OK for around 225’ish rwkw (300 rwhp). But I have only seen that once in over 50 R33GTST’s. The rest have dropped off from 205 rwkw (275 rwhp) onwards, with around 215 rwkw (290 rwhp) being the most common.

An adjustable FPR (eg; Nismo bolt style $150 from Nengun) will facilitate an increase in fuel pressure. It isn’t linear though, a 10% increase in pressure doesn’t equal a 10% increase in flow. For example increasing the base pressure to say 46 psi (30%) enables the standard injectors to stretch to around 400 cc’s (up from 370 cc which is 8%). That’s enough for 235 rwkw (320 rwhp) which his about as far as I would recommend going. The fuel pressure gets too high for the standard size hoses and clamps and fuel fires are very nasty. Hence why I suggest replacing the 10 + year old fuel hoses with new ones. Plus Walbro pumps are not very good at handling pressure, their flow drops off rather dramatically.

A spot 97% injector duty reading is not a very good indication, it may well have been 85% duty, plus 12% for acceleration enrichment. Try looking at the injector duty as you run up through the rpm range at WOT in 3rd and 4th gear (a passenger is handy for that). That is a far better indicator.

The GCG high flow is good for around 265 rwkw (355 rwhp). So if you want to use the full potential of the turbo upgrade you really need to be looking at aftermarket injectors.

Hope that was of some help

cheers

PS; if you had done a search you would have found all of the above written by me many, many times.

[Steve]

Aftermarket injectors designed for use on other engines (that may or may not require adaptors to fit RB25’s) may or may not be specified for the same fuel pressure. Their operating and flow rating are specified. BUT (there is always a but) I have not found any injectors that use different fuel pressures that will fit RB25’s

let me help you out then, HKS, Sard, Apex

I havent done the testing myself, just basing this on what has been published (by AP racing) and what I have been told by signal japan - all rated and should be run on 3.0kg base pressure at idle. This was based on trial and error, as explained to me, especially with larger injectors, its difficult to get a nice idle with factory fuel pressure - can be done, but its easier (and better) to use 3.0kg - but hey, they are probably just a bunch of dump Japanese, what would they know.

Another thing to remeber, if you fit say sard 550cc injectors, and only run the factory base fuel pressure, the injector correction and lag adjustment will be different (510cc v's 550cc, +0.06ms vs +0.08ms)

- or dont you consider this an important factor?

[Sydneykid]

let me help you out then, HKS, Sard, Apex

I havent done the testing myself, just basing this on what has been published (by AP racing) and what I have been told by signal japan - all rated and should be run on 3.0kg base pressure at idle. This was based on trial and error, as explained to me, especially with larger injectors, its difficult to get a nice idle with factory fuel pressure - can be done, but its easier (and better) to use 3.0kg - but hey, they are probably just a bunch of dump Japanese, what would they know.

Another thing to remeber, if you fit say sard 550cc injectors, and only run the factory base fuel pressure, the injector correction and lag adjustment will be different (510cc v's 550cc, +0.06ms vs +0.08ms)

- or dont you consider this an important factor?

2.5 bar rail pressure plus the normal 0.5 bar vacuum at idle = 3.0 bar

cheers

Edited October 25, 2006 by Sydneykid

[Steve]

what the?

sorry, not following what you are saying

nissan manuals state stock rail pressure as 2.55kg at idle, 3.05kg at atmosphere, their injectors are rated at 2.55kg, ie, idle (rb25 - 370cc at 2.55kg, 410cc at 3.05kg etc)

Sard, apex, hks rate their injectors at 3.0kg at idle

how are these the same????

[Sydneykid]

what the?

sorry, not following what you are saying

nissan manuals state stock rail pressure as 2.55kg at idle, 3.05kg at atmosphere, their injectors are rated at 2.55kg, ie, idle (rb25 - 370cc at 2.55kg, 410cc at 3.05kg etc)

Sard, apex, hks rate their injectors at 3.0kg at idle

how are these the same????

Nissan (and Nismo) know that the RB produces 0.5 bar at idle, hence they can specify 2.5 + 0.5 = 3.0.

Sard, Apexi, HKS only know what their injectors flow at 3.0 bar, so that's the only number that they can specify. Keep in mind that Jecs make Nissan annd Nismo injectors and Denso make pretty much everything else.

Real world proof, if I stick a 550 cc Nismo injector on the flow bench at 3.0 bar and compare it with a 550 cc Sard injector at 3.0 bar, I end up with pretty much the same flow rates (ie; ~550 cc per minute).

There are exceptions, Rochester for example.

cheers

[Steve]

but nissan fuel pressure at idle is 2.55kg, not 3kg - thus why I was saying a fuel pressure reg is worthwhile.

[letemlaf]

OK, he says puting his hand up, that would be me.

Aftermarket injectors (eg; Nismo) designed for use with RB25’s use the standard Nissan fuel pressure, which is 34-36 psi (2.3 to 2.5 bar). Aftermarket injectors designed for use on other engines (that may or may not require adaptors to fit RB25’s) may or may not be specified for the same fuel pressure. Their operating and flow rating are specified. BUT (there is always a but) I have not found any injectors that use different fuel pressures that will fit RB25’s.

So while you are right in theory, in the real world that is simply not the case.

Plus I defy anyone to tell the difference in spray patterns between 2.5 and 3 bar base pressure. Remember injectors in turbo engines have to have good spray patterns at absolute pressures ranging from 2.0 to 6.0 bar (plus or minus vacuum and boost). So 0.5 bar is neither here nor there as far as their spray pattern is concerned. This is not always the case in injectors intended for N/A use however. Rochesters for example, like to have their specified fuel pressure at all times and don’t handle drastic increases or decreases.

Back to the original question. With a perfect tune and an engine in perfect condition the standard injectors are OK for around 225’ish rwkw (300 rwhp). But I have only seen that once in over 50 R33GTST’s. The rest have dropped off from 205 rwkw (275 rwhp) onwards, with around 215 rwkw (290 rwhp) being the most common.

An adjustable FPR (eg; Nismo bolt style $150 from Nengun) will facilitate an increase in fuel pressure. It isn’t linear though, a 10% increase in pressure doesn’t equal a 10% increase in flow. For example increasing the base pressure to say 46 psi (30%) enables the standard injectors to stretch to around 400 cc’s (up from 370 cc which is 8%). That’s enough for 235 rwkw (320 rwhp) which his about as far as I would recommend going. The fuel pressure gets too high for the standard size hoses and clamps and fuel fires are very nasty. Hence why I suggest replacing the 10 + year old fuel hoses with new ones. Plus Walbro pumps are not very good at handling pressure, their flow drops off rather dramatically.

A spot 97% injector duty reading is not a very good indication, it may well have been 85% duty, plus 12% for acceleration enrichment. Try looking at the injector duty as you run up through the rpm range at WOT in 3rd and 4th gear (a passenger is handy for that). That is a far better indicator.

The GCG high flow is good for around 265 rwkw (355 rwhp). So if you want to use the full potential of the turbo upgrade you really need to be looking at aftermarket injectors.

Hope that was of some help

cheers

PS; if you had done a search you would have found all of the above written by me many, many times.

What sort of power can the walbro pumps handle up to? or are you saying their not very reliable from the word go?

Btw, i have read many of your post's sydneykid, they are most helpful!

[Sydneykid]

but nissan fuel pressure at idle is 2.55kg, not 3kg - thus why I was saying a fuel pressure reg is worthwhile.

Yes, but it has 0.5 bar of sucking (vacuum) helping the injectors flow. Hence the "real" pressure is 3.0 bar. The 3.0 bar is the pressure differential between the fuel rail and the inlet port.

As usual the numbers tell the story;

2.5 - -0.5 = 3.0

The 3.0 bar is the pressure differential between the fuel rail (2.5) and the inlet port (-0.5).

Same applies when there is boost in the inlet port, except boost is a "+" of course

4.0 - + 1.0 = 3.0

The 3.0 bar is the pressure differential between the fuel rail (4.0) and the inlet port (1.0).

cheers

[Sydneykid]

What sort of power can the walbro pumps handle up to? or are you saying their not very reliable from the word go?

Btw, i have read many of your post's sydneykid, they are most helpful!

Do a search “Sydneykid”, Walbro” and “any date”. I have posted up the test results of what happens to the flow of a Walbro pump when it has to pump against boost pressure.

cheers

[Steve]

well if that be the case, factory RB25 injectors would flow 410cc, but they dont, they are 370cc -

RB25/SR20 -- stated inj flow, 370cc, tested at 2.55kg - 370cc, at 3.05kg - 410cc

Sard 550cc -- stated inj flow, 550cc, tested at 2.55kg - 510cc, at 3.05kg - 560cc

Apexi 740cc -- stated inj flow, 740cc, tested at 2.55kg - 675cc, at 3.05kg - 740cc

Now why would nissan rate their injectors lower than they actually are, because following your logic, they are in fact 410cc, not 370...

AP engineering and Nissan are obviously wrong, following your theories.

[Steve]

For those interested, with thanks to AP engineering (and cubes for copying them before they went off line )

Very handy reference, esp for caclulating injector correction and lag time correction

Top feed (sorry about the small size, if you right click and save image as, you can easily zoom in - for those interested anyways)

Side feed

[bazr33]

Hi Guys , im in the situation where i am upgrading injectors + z32 AFM and Nismo Fuel reg + apexi super intake filter

Should i consider upgrading my fuel hoses.

Im running at the moment

PFC

AVCR

R33 standard hiflow plain bearing (12psi)

Walbro fuel pump

Split dump to hiflow cat.

I have 306rwhp, i am upping the boost to 15psi when i get my tune.

I also have oil cooler kit, oil catch can, getting put on by myself after tune has been done.

I just saw that word fire, and yeah not a big fan.

So anything that i can get for my car to be relatively safe , would be pretty helpful.

And Letemlaf, my car is pretty much on 65% duty and my afm is close to maxin out. on 306rwhp. And yeah getting the other stuff being put on next week, by one of the best performance places i have been too.

i'll let ya know how it goes, and if my car catches on fire or blows up.

[Steve]

Look at them, and see if they are in good condition or not (no signs of bulging/cracking etc). If they look tired, replace them - they should be inspected when you service the car, but sometimes people get lazy.

I made over 400rwhp with stock fuel lines, but I did preplace the rubber hoses that run to/from the fuel rail, because they looked a bit tired.

[700HP-GTR33]

Injectors are not going to get you there.

You need to upgrade your turbo and make sure all your supporting mods are there for the power level....

ie.Oil cooler for oil,catch can,etc,etc....

You also do not have a boost controller.so you will need one withthe new turbo

So before you change injectors and spend all that money on fuel mods. get the power up.

I am a bit confused too...are you saying your injectors are maxing out or are you asking

us if they would be.....the answer is no with the mods you have.

Cheers

[Steve]

this was the only question I saw

Should i consider upgrading my fuel hoses

[letemlaf]

Injectors are not going to get you there.

You need to upgrade your turbo and make sure all your supporting mods are there for the power level....

ie.Oil cooler for oil,catch can,etc,etc....

You also do not have a boost controller.so you will need one withthe new turbo

So before you change injectors and spend all that money on fuel mods. get the power up.

I am a bit confused too...are you saying your injectors are maxing out or are you asking

us if they would be.....the answer is no with the mods you have.

Cheers

Yeah, i was a little confused because my workshop said they will be right on the limit and from what ive read on here they should be good for alot more power than what i have.

I just replaced my fuel filter because it was over due, from what i can tell i am hitting about the 89% duty in 3rd gear. But ill see how it goes over the next few days

[700HP-GTR33]

Put some injector cleaner into your fuel tank and see if this helps.