Fuel Injectors & Fuel Rail

[Boost Junky 1]

As most of you know im most of the way through turboing my E30-M50. I am now at the point of considering which injectors too use.

Now, my main issues are:

- What injectors will fit my factory fuel rail/intake manifold setup?

- What size do I need to be using?

- Are there any bmw injectors that flow enough that will be a direct replacement?, and

- Is it worth going an aftermarket fuel rail and will it widen my options of which injectors I could use?

Cheers guys any help appreciated

Luke

[Mike 1]

http://www.turbochargingdynamics.com/subca...2-Injectors.php

I'm pretty sure BMW are pretty universal through the models, so those should be ok.

People have also used Ford ones before as they use bosch injectors too (or same size), so maybe could be worth looking at some from an XR6 turbo. short of the 6 cyl M3's i doubt you'll find any worthwhile from BMW. even the M3 or XR6 ones wont give you much breathing room if you get silly with boost.

Google can find you some great calculators to help with this sort of thing

[CamB 48]

Yeah - what Mike said about using google to figure out your injector size needs.

I believe it is standard Bosch injectors (14mm? - not sure on what the way to refer to the size is). The XR6 Turbo (~300cc I think) or supercharged Holden 6 injectors (370cc?) might get you to your goal. ... depending on the goal (eg if less than 400hp). It is unlikely any BMW injectors will get you there coz BMW tend to size them just big enough for the power the engine has - like Mike says, maybe M3.

The standard fuel rail can apparently flow enough for all but the silliest power levels. The standard fuel pressure regulator is fine, but if you get an adjustable one you can raise the fuel pressure (somewhat - too much is unsafe) which means you can get away with smaller injectors.

If it was me, I wouldn't bother buying an adjustable FPR or aftermarket fuel rail. I would spend that money making sure I bought big enough injectors to work with the factory FPR.

You should also make sure you buy injectors with the right impedence to work with your computer (whatever that may be).

[Boost Junky 1]

Thanks both Mike and Cam. I will have a hunt on google and calculate a required size vs my target power output whatever that may be, wont be too high (for now)

I will flag any standard BMW injectors then, what CC are the M50 ones standard if anyone knows? The XR6 Turbo ones could be a possibility I mean they run a GT3540 Turbo also just depends what the factory injectors in those things are good for?

Ok I will stick with my factory fuel rail then, that will save some $$ and allow me to maintain the factory cover that sits on top of the injector rail.

Damn I have already purchased a SARD rising rate FPR last year, I may as well use it even if its doint the same or not much more than the factory FPR. I only read not so long ago that the factory one was good for upto 32psi, in saying so I have also read about the factory ECU being good for upto 18psi. None the less I still purchased a Link G3 for control over the system which i believe was a good move. So that answers your question about my computer Cam.

Cheers again guys

Luke

[CamB 48]

Yeah - you should get high impedence injectors. From memory you need a LinkPlus G3 to run low impedance injectors. It's not really any issue for smaller injectors, but I ended up with low impedence 590cc ones (wooooo, huge - a bit big really for my needs, but I have a 2.5bar regulator not a 3 bar) so I need to run resistors with them.

I got them coz it is hard to find high impedance injectors in larger sizes at good prices.

A quick google suggests the ones you have are only around 170cc. I would have thought you'd want at least 300c, even if you keep the Sard and can turn up the pressure a little.

This might help with a list of some of the options. It is pretty hard to find factory Bosch-style injectors you can buy second-hand over about 400cc:

http://www.injectorsonline.com/indivprod.p...=74&scid=11

If you buy second hand I would recommend flow testing, but I am a bit of a nana.

Edited January 22, 2009 by CamB

[Boost Junky 1]

Ah yup so run High impendance injectors with my normal Link G3 if im getting bigger injectors right? I dont understand why you need to run resistors with a 2.5bar FPR? Or did u mean you have to run resistors because of the injectors being low impendance haha? Those high impendance 440cc 'Green Top' injectors arent too bad in price and they are high impendance.

Ahh only 170cc haha ok im definitely going to upgrade. I will run the SARD and run 440cc or near abouts. I was running 450cc VR4 injectors when i turboed my integra.

Yea I will probably buy brand new ones Cam, the VR4 ones I used on the teg were 2nd hand and I had my mate flow test them.

Thanks again

Luke

[CamB 48]

Yeah - poorly worded by me:

1) I needed resistors coz I got low impedance injectors

2) I got low impedance injectors since it is hard to find larger Bosch injectors second hand in high impedance

3) I got large ones partly because that was what I found, partly because I only have 4 cylinders (for 2.1 litres), and partly because the M10's pressure regulator is 2.5 bar and usually injectors are rated at 3 bar (so I will only have the equivalent of 500cc).

I mean its still enough for something like 400hp, so realistically I am way oversized...

Edited January 22, 2009 by CamB

[Boost Junky 1]

Haha all good man.

Yea thought so, still not completly up with injectors as far as impendance goes and what not but had some idea.

So your injectors wont flow as much because the FPR is not holding the fuel pressure as high as obviously a 3.0bar..

Yea how much power are you putting out? 400hp is alot of power so that is true but nothing wrong with having more than enough there though, especially if you want to wind things up a little bit more in the future haha. As long as you dont have a risiing rate FPR and whack the pressure way up is what you were saying earlier right?

Is this dangerous in the sense that it will do damage to your motor or dangerous in a sense that too much pressure my might burst something and cause a fire haha?

Edited January 22, 2009 by Boost Junky

[CamB 48]

Yeah there is some limit over which you shouldn't run the fuel system - I don't recall what or why - plus higher pressures can be harder on the fuel pump.

Don't forget that the FPR increases pressure under boost - if its a 3 bar FPR and ou have 1 bar of boost it is 4 bar going to the injectors ... which is good coz they have to fight 1 bar of pressure in the manifold. So if you have a higher pressure set on the FPR, and run lots of boost, the pressure can get really high in the pressure side of the fuel system

I will be extremely happy with anything over 200hp at the wheels, since that will be fast enough for my driving skillz.

[Mike 1]

As far as I know a rising rate FPR can cause a few issues, basically it complicates how much fuel the ECU thinks its putting in. A factory FPR maintains a constant relative pressure between the fuel rail and the manifold, which is what you want. (as cam mentions above)

Word of warning: Mitsi injectors generally dont fit straight into our fuel rails, require a bit of modding, but can usually be done. Talk to a proper fuel injection shop if your serious about this.

IMO just keep your fuel pressure at 3 bar (~43.5psi). Its close what most injectors are designed to run at and should still give good atomisation. I can't remember the formula but raising pressure by 25% doesn't give you 25% more flow, its less than that, depends on square root of difference or something along those lines.

Also, no point going way bigger than you need (a little head-room is a good thing though), just makes it harder to tune, especially at idle.

[CamB 48]

Also, no point going way bigger than you need (a little head-room is a good thing though), just makes it harder to tune, especially at idle.

I absolutely agree with this - do as I say, not as I do. Mind you, I wanted 400hp headroom, and a decent idle and cruising economy isn't a priority on a race car.

[Boost Junky 1]

As far as I know a rising rate FPR can cause a few issues, basically it complicates how much fuel the ECU thinks its putting in. A factory FPR maintains a constant relative pressure between the fuel rail and the manifold, which is what you want. (as cam mentions above)

Word of warning: Mitsi injectors generally dont fit straight into our fuel rails, require a bit of modding, but can usually be done. Talk to a proper fuel injection shop if your serious about this.

IMO just keep your fuel pressure at 3 bar (~43.5psi). Its close what most injectors are designed to run at and should still give good atomisation. I can't remember the formula but raising pressure by 25% doesn't give you 25% more flow, its less than that, depends on square root of difference or something along those lines.

Also, no point going way bigger than you need (a little head-room is a good thing though), just makes it harder to tune, especially at idle.

Oh ok, but wouldnt the car be tuner whos tuning my car tune to counter for what the FPR is doing? Sorry this isnt as clear to me as you guys haha. In saying what you guys have said, what is the point in aftermarket rising rate FPR's then?

Oh no haha I wont be purchasing any Mitsi injectors mike, but when I did for the Integra I had to get different seals for where the the injectors sit in the intake manifold in order for the injectors to fit corectly.

Ah right so if you were too raise it by 100% your not going to double your pressure etc?

I absolutely agree with this - do as I say, not as I do. Mind you, I wanted 400hp headroom, and a decent idle and cruising economy isn't a priority on a race car.

So whats the deal with idle, what effects it?

[CamB 48]

If the injector is too big you can't get it to fire for a short enough time (and or if you do it doesn't spray the fuel well etc) so you get a poor idle (or something like that). Ask me once mine is running...

The FPR you have is fine for what you want. If its not it is easy to change (just further pain on the wallet).

[Mike 1]

Oh ok, but wouldnt the car be tuner whos tuning my car tune to counter for what the FPR is doing? Sorry this isnt as clear to me as you guys haha. In saying what you guys have said, what is the point in aftermarket rising rate FPR's then?

Ah right so if you were too raise it by 100% your not going to double your pressure etc?

So whats the deal with idle, what effects it?

I imagine a few more are also reading this who might be a bit lost so I'll go back a few steps; bear with me if its too simple.

Injectors are connected between your fuel rail and intake manifold. The fuel pressure regulator is supposed to keep the fuel pressure constant.problem is that the pressure in the intake manifold varies considerably, from near vacuum to serveral times atmospheric in turbo motors.

Lets say that the static fuel pressure is 3 bar (ie 3 times standard atmospheric pressure). If your intake manifold pressure is -0.5bar then the effective pressure your fuel injectors are operating at is 3.5 bar (the difference between the fuel rail and manifold). This is quite higher than the 3bar static, so the FPR (fuel pressure reg) is connected to the intake manifold so that when the rail is at -0.5bar the rail pressure is at 2.5bar so the pressure difference is 3bar. this keeps the injectors flowing the same amount for a given opening time and the ECU is happy.

A number of after market ECU's will only raise the 'static' pressure (ie from 3bar to 3.5bar). this is fine to squeeze a little more out of your injectors or for fine tuning if you dont have and aftermarket ECU.

Problem is with a rising rate fuel pressure regs (RRFPR). A normal FPR is designed to keep that pressure difference constant so the injectors flow the same the whole time. A RRFPR doesn't, is raises the fuel rail pressure at the rate it was designed for. ie if the intake manifold pressure rises to 1.1bar (0.1 bar boost) and its a 10:1 RRFPR then the rail pressure rises to 5 bar. remember the rail is over 1bar so the fuel rail is already at 4 bar to keep the difference at 3 bar. however that extra 0.1bar raises fuel pressure by 10 times the manifold. So 10x0.1=1bar. which gives the injectors a pressure of 4 bar. (as said before this isn't 25% more fuel, much less infact)

The reason for this is to inject more fuel when a standard ECU has been boosted and it can't recognise the boost pressure, so we use the extra pressure to inject more fuel and keep the mix right, otherwise the extra air would go unrecognised and we would run lean.

A tuner or suitable software can counter for a RRFPR simply by adjusting the fuel maps but its extra work and a waste of money for the RRFPR, as any extra fuel from the injectors will be reduced by the ECU at that given pressure.

Ah right so if you were too raise it by 100% your not going to double your pressure etc?

exactly, double the pressure only gives you an extra 40% more flow. google can find you calculators to work out the difference for this also.

As for ease of tuning- as Cam said the injector can only open for a finite time. Get massive injectors and by the time it take the ECU to open and close them as fast as it can you've already injected too much fuel. you get much greater precision with smaller injectors

Luke, hope that clears things up. If anyone else has been reading and is still a bit lost just ask, because I'm sure you wont be the only one.

(edit- That my understanding of how it all works, happy to be corrected by more knowledgable people)

Edited January 23, 2009 by Mike

[Boost Junky 1]

Whoa, well that clears alot of things up Mike. I now understand that the vacuum or boost in the manifold adds to the amount of pressure in the rail via the vacuum/boost line that runs to the FPR. So this keeps the correct amount of static fuel pressure coming out of the injector. Obviously this static fuel pressure rises with the extra air flow coming into your manifold as you give the motor more revs, but that amount of extra fuel is controled by the ECU correct?

I always thought the FPR controled how much fuel is injected where as now I understand it controls the pressure at which it is released?

Were all your figures correct Mike as I got a little lost where you were explaining how if the manifold pressure rises to 1.1bar (0.1 bar of boost) then a 10:1 RRFPR would raise the pressure to 5 bar at the fuel rail. How is 1.1 bar, 0.1 bar of boost? 1.1 bar is 1.1 bar i would have thought... still not a 100% clear on how the RRFPR works especially when ratios are involved lol im not too good with them..

Thanks cam, so obviously bigger injectors have a longer opening period which is good for high power setups where they need alot more fuel to compensate for the extra air being forced into the manifold. But they are a bit much for idle where you have vacuum and dont need much fuel at all? This is because they have a longer minimum opening period correct?

Haha what a science lecture we got going here... im not sure if any of that made sense but it sure is interesting

Luke

[CamB 48]

Thanks cam, so obviously bigger injectors have a longer opening period which is good for high power setups where they need alot more fuel to compensate for the extra air being forced into the manifold. But they are a bit much for idle where you have vacuum and dont need much fuel at all? This is because they have a longer minimum opening period correct?

Not quite - they have a bigger hole (or more holes, occasionally), so they flow more for the same opening period.

The downside is that because of the bigger hole, it is hard to send a short enough pulse at idle.

On the FPR, I think the best way for you to clear it up is to figure out if the adjustable one you have is:

1) rising rate; and

2) what the ratio is.

It could be a suitable ratio.I think the Sard ones are 1:1 ratio, which I believe is fine.

[Mike 1]

Obviously this static fuel pressure rises with the extra air flow coming into your manifold as you give the motor more revs, but that amount of extra fuel is controled by the ECU correct?

um, not sure what you mean here. manifold pressure normally depends on engine loading, high loads have less vacuum. the ECU acounts for the extra fuel at higher rpm by opening the injectors for longer

I always thought the FPR controled how much fuel is injected where as now I understand it controls the pressure at which it is released?

yip

Were all your figures correct Mike as I got a little lost where you were explaining how if the manifold pressure rises to 1.1bar (0.1 bar of boost) then a 10:1 RRFPR would raise the pressure to 5 bar at the fuel rail. How is 1.1 bar, 0.1 bar of boost? 1.1 bar is 1.1 bar i would have thought... still not a 100% clear on how the RRFPR works especially when ratios are involved lol im not too good with them..

1bar is atmospheric so anything above that is boost pressure. I'm not sure when the RRFPR begins to raise fuel pressure at the higher rate, I assumed it started raising at 10:1 when over 1bar manifold pressure is reached.

[Boost Junky 1]

Not quite - they have a bigger hole (or more holes, occasionally), so they flow more for the same opening period.

The downside is that because of the bigger hole, it is hard to send a short enough pulse at idle.

On the FPR, I think the best way for you to clear it up is to figure out if the adjustable one you have is:

1) rising rate; and

2) what the ratio is.

It could be a suitable ratio.I think the Sard ones are 1:1 ratio, which I believe is fine.

Oh yes i get ya now. Because of the extra holes/bigger holes, more fuel is going to come out in the same ammount of time that fuel would come out if there were less holes/smaller holes. Im sure the SARD RRFPR's are rising rate, problem is the manual that came with it is all in Japanese and so is the box. Only thing I can see on the regulator itself is "SARD FUEL REGULATOR" and under that "200-800kpa....

Ohh of course Mike. Because there is a certain amount of pressure in our atmosphere already which is 1bar as you said got it now. I would have thought that also because you are starting to get possitive pressure in the manifold...