Fuel Pressure Adjustment

[nightstocker99]

I have a 2g GST. right now i am trying to correctly tune the fuel system to the evo iii 16g. I am now attempting to run 15 psi of boost. The formula that i have used says that i need to flow about 553.26 cc/min, not to much over the stock injectors, but not enough to run 650 injectors.

Does anyone know what the stock duty cycle of the 450 injectors?

I have a formula that tells me to bump up the stock fuel pressure from 43psi to 65psi.

Can anyone tell me if that is correct to?

The other formula tells me i need to run about 100 psi of fuel!

This is where i need the help. I am not sure which formula is correct.

 

[synthetek]

Do you have an adjustable fuel pressure regulator? you set the base fuel pressure at 43 PSI at ldle with the vacuum line off, then your fuel pressure regulator will raise the fuel pressure as needed.

 

[nightstocker99]

i am going to buy one after i figure this out. please explain more! how can the pressure adjust itself. and how do you know when you are injecting to much fuel into the system. the pcm wouldnt know that you need 553 cc not 450cc to run correctly. i know i have to either turn the pressure up or buy bigger ones, or tell the pcm that i have bigger injectors which requires pcm tuning or a rescaled maf sensor.

 

[Bud92gsx]

Running 550 cc's on 450s with a stock fuel system and no tuning device.Best idea Ever.

 

[Seamus]

well, its no exact science and i do not recomend this, but if you are too cheap, oyu can restrict your return line until oyu get the desired pressure. with out an AFPR, there is no exact science to it. You car is going to run like dog shit, especially at idle.

i'm not going to tell you how to do it. If you are smart enough to figure that out on your own, you may have enough sense to make this work very half ass. If oyu have no clue how to do it, then there isn't a chance in hell this will end in anything but disaster.

 

[nightstocker99]

well sir i know what i am talking about and there is a formula to figure out your fuel pressure. you have to know what you are pulsing which at this point is 450cc for every 1psi of boost you increase you have to adjust the fuel pressure 10psi more. that would bring the fuel pressure up to 65 psi.

then there is also a formula that requires algebra which is pretty easy to figure out. you just have to know what your flow rate and pressure rate are and know what you are going to and the the algebra comes into play and that tells you the new flow rate and pressure rate.

I am in no way cheap. i am not even asking about parts.

well, its no exact science and i do not recomend this, but if you are too cheap, oyu can restrict your return line until oyu get the desired pressure. with out an AFPR, there is no exact science to it. You car is going to run like dog shit, especially at idle.

i'm not going to tell you how to do it. If you are smart enough to figure that out on your own, you may have enough sense to make this work very half ass. If oyu have no clue how to do it, then there isn't a chance in hell this will end in anything but disaster.

 

[Seamus]

well we know which category you will fall into.

ahh I see you edited the post after it was in my browser. You don't want to raise your base fuel pressure a bunch without a afpr anymore?

well sir i know what i am talking about and there is a formula to figure out your fuel pressure. you have to know what you are pulsing which at this point is 450cc for every 1psi of boost you increase you have to adjust the fuel pressure 10psi more. that would bring the fuel pressure up to 65 psi.

then there is also a formula that requires algebra which is pretty easy to figure out. you just have to know what your flow rate and pressure rate are and know what you are going to and the the algebra comes into play and that tells you the new flow rate and pressure rate.

I am in no way cheap. i am not even asking about parts.

 

[007jimmy]

well sir i know what i am talking about and there is a formula to figure out your fuel pressure. you have to know what you are pulsing which at this point is 450cc for every 1psi of boost you increase you have to adjust the fuel pressure 10psi more. that would bring the fuel pressure up to 65 psi.

then there is also a formula that requires algebra which is pretty easy to figure out. you just have to know what your flow rate and pressure rate are and know what you are going to and the the algebra comes into play and that tells you the new flow rate and pressure rate.

I am in no way cheap. i am not even asking about parts.

You are seriously over thinking this. To run more then stock boost on a upgraded turbo you need more fuel. Stock 2g fuel system just isn't going to cut it, no matter what fuel pressure you set it to. Period.....

 

[synthetek]

i am going to buy one after i figure this out. please explain more! how can the pressure adjust itself. and how do you know when you are injecting to much fuel into the system. the pcm wouldnt know that you need 553 cc not 450cc to run correctly. i know i have to either turn the pressure up or buy bigger ones, or tell the pcm that i have bigger injectors which requires pcm tuning or a rescaled maf sensor.

To run larger than stock injectors you wil need some type of tuning device, AFC, MAFT translator. dsmlink, etc...

please explain more! how can the pressure adjust itself

The vacuum line that runs to the fuel pressure regulator makes the fuel pressure raise 1:1

 

[nightstocker99]

I know i would need a programmer of some sort.

To run larger than stock injectors you wil need some type of tuning device, AFC, MAFT translator. dsmlink, etc...



The vacuum line that runs to the fuel pressure regulator makes the fuel pressure raise 1:1

ok so maybe i am not clear with what i mean.

i know i need to fuel pressure regulator i know that i will need to get the car tuned to the new fuel trim.

there are two things you can do get bigger injectors easy thing to do, I can just search online.

or

you can turn up the fuel pressure to that the injectors and the fuel pressure will now force more fuel through the injector, so long as the injectors do not reach max duty cycle of 805 after 80% the injectors will not have enough time to close and they will end up hanging open causing new problems.

well we know which category you will fall into.

ahh I see you edited the post after it was in my browser. You don't want to raise your base fuel pressure a bunch without a afpr anymore?

what do you mean by that sir. what category is it that i fall into.

i am going to get an afpr or else i wouldn't be able to raise the pressure.

 

[Lofty]

You set your base fuel pressure which is around 40 or so for a 2g, it raises it for the boost level you are running.

It adjusts PRESSURE itself. All you have to do is set fuel pressure to idle and the AFPR does the rest for you.

So given you have DSMlink or something to tune with, a wideband, and big enough fuel pump and injectors, the rest is controlled by DSMlink and your AFPR, which, as stated, is set once.

You're thinking too much into this.

And yes, I know what you are talking about. If you bump up fuel pressure on 450s it will make them flow more.... but that is the ass backwards way to tune.

 

[bastarddsm]

And yes, I know what you are talking about. If you bump up fuel pressure on 450s it will make them flow more.... but that is the ass backwards way to tune.

Ehh. Not really. If your just barely running out of injector, there is no reason not to bump for bfp up to make the injectors flow more.

Example, on a 1g that runs a stupid low bfp of 37psi, bumping up to 47psi( 1g n/t fp) makes your 450's look like 510's to the ecu....pretty substantial increase.

Granted, this all depends that you have the fuel pump for it. I'd reccomend running a 255hp, if you plan on running 20psi+ with an elevated BFP.

 

[Lofty]

Yes, I know.

He's not talking about barely running out of injector though, he's talking about solely tuning with fuel pressure and getting a bit confused with how things work.

 

[phunny]

"A bit confused", lets call an apple an apple please. That wouldn't be too bad as no one knows it all but the arrogance is a bit too much to take.

First, why are you even talking about tuning anything when you clearly do not have the proper equipment? After you gather your parts then maybe you can do some research and get things going in the proper direction.

Second, raising the fuel pressure to try and get the fuel needed is a horrible idea. The car automatically adjusts the fuel pressure for boost... Why would you think the car needs you to adjust the pressure for boost? Fuel pressure for a 2G is 43.5 psi, set it, leave it alone.

Thirdly, why don't you start by choosing a goal and then creating a build plan from there as all this other crap is really going to get you nowhere.

 

[RamenPride]

ok so maybe i am not clear with what i mean.

i know i need to fuel pressure regulator i know that i will need to get the car tuned to the new fuel trim.

there are two things you can do get bigger injectors easy thing to do, I can just search online.

or

you can turn up the fuel pressure to that the injectors and the fuel pressure will now force more fuel through the injector, so long as the injectors do not reach max duty cycle of 805 after 80% the injectors will not have enough time to close and they will end up hanging open causing new problems.


i am going to get an afpr or else i wouldn't be able to raise the pressure.

You can use something like the B&M Commandflo to increase your base fuel pressure if this is what you're looking to do. However, keep in mind that by increasing your base fuel pressure to get the injectors to put out more fuel, you're causing the fuel pump to do more work. Unless it's meant for high fuel pressures, it will die quickly.

AFPR's are usually used to lower the fuel pressure with a bigger fuel pump. Fuel pressure will then rise 1:1 with boost.

 

[jtmcinder]

Ehh. Not really. If your just barely running out of injector, there is no reason not to bump for bfp up to make the injectors flow more.

I know that you love arguing and that you are, technically, correct. But have you read the whole thread carefully or did you just look for the one thing that could argue about? If you had read the whole thread carefully, then you'd know that the OP is pretty much clueless about tuning. And if you cared about the members of the site, as well, then you would not have said the above, just to be clever; you would have realized that the OP is in way over his or her head and posted something remedial or just stayed out of it.

 

[nightstocker99]

I am not clueless

I know that you love arguing and that you are, technically, correct. But have you read the whole thread carefully or did you just look for the one thing that could argue about? If you had read the whole thread carefully, then you'd know that the OP is pretty much clueless about tuning. And if you cared about the members of the site, as well, then you would not have said the above, just to be clever; you would have realized that the OP is in way over his or her head and posted something remedial or just stayed out of it.

Here is the formula for fuel pressure adjustment

F2=(Square Root of P2 divided by P1) x F1

From Power and Performance II in Chapter 4 Fuel System from UTI

they could be wrong but then that would be 45 years of false information giving to 1 million students.

That is my reference

their is no square root symbol

so

p1 is your original fuel pressure
p2 is what the new pressure will be
f1 is what the injector currently flows
f2 is what the new flow rate is

so

f2= (square root of 65psi divided by 43psi) x 450cc
f2= (square root of 1.51) x 450
f2= 1.229 x 450
f2 = 553.05cc

I got p2 from the general rule of thumb of increase fuel in proportion to boost pressure

typically increase fuel pressure 10 to 12psi for every 1 pound of boost increased
I choose to increase 11psi of fuel for every pis of boost.

that rule will change form application to application.

That is the math right there. I am not saying I am correct. I am asking if anyone agrees.

 

[Lofty]

Did you even read what I or anyone else said? Youre way over your head.

 

[nightstocker99]

how is that

i have just asked questions,not one person has answer my question about duty cycle of the injector you all just tell me I am stupid.

Does anyone know what duty cycle is?

If you arent going to help then please dont post. read the rules

 

[Lofty]

You are doing un-needed calculations when everyone has already explained.

You are not listening. Kinda humorous you just made a post saying nobody here knows whats going on.




Good luck.

 

[nightstocker99]

Did you even read what I or anyone else said? Youre way over your head.

I have read all of the post everyone has posted in this thread

 

[jtmcinder]

With regard to this question you asked that nobody has answered, is it this one?

Does anyone know what the stock duty cycle of the 450 injectors?

Because the asking of this question - assuming that it isn't one huge typo - was my first big hint that you are clueless.

With that said, it would be very easy to, for example, add just one word to your question and, thereby, change it from being silly to being reasonable. Please feel free to edit the question to make it reasonable.

 

[bastarddsm]

^ I was half in the bag last night. . I think the correct thing to do here is send this guy on a mission to read exactly how efi works. Then have him explain his calculations.

I'm getting the feeling that the OP doesn't understand that the ecu can measure the extra airflow generated by the 16g and extra boost. And that it will automatically inject the extra fuel.

 

[jtmcinder]

Cool.

 

[bastarddsm]

I got p2 from the general rule of thumb of increase fuel in proportion to boost pressure

typically increase fuel pressure 10 to 12psi for every 1 pound of boost increased
I choose to increase 11psi of fuel for every pis of boost.

that rule will change form application to application.

That is the math right there. I am not saying I am correct. I am asking if anyone agrees.

I see the problem here. Your rule of thumb is only applicable for guys that are running a Vortech FMU style system. This is used on n/t cars that are turboed. They make up for the computers inability to add the extra fuel needed for boost by making the fuel pressure go sky high.

Those systems work by blocking off the boost signal to the ecu, so that the ecu thinks the manifold is at 0psi. The injector pulse width is as high as it can go. The FMU then jacks the pressure up to get the injectors to flow the extra fuel needed for boost. This system revolves around the fact that the amount of fuel isn't that important as long as there is enough of it.


You don't have to do that, Your GST came factory equipped with an ecu that can measure the extra airflow caused by extra boost, so you don't need to do any of that funny stuff. You need to pick your injector size based on your power output. Then get some sort of a tuning soluton.


You also need to go out and read about the differences between GAUGE PRESSURE, ABSOLUTE PRESSURE, and PRESSURE DIFFERENTIAL.

Let me lay this down for you.

The GAUGE FUEL PRESSURE, does in fact rise 1psi for every psi of boost, but the pressure differential across the injectors STAYS THE SAME, because the boost counteracts it. The pressure differential across the injectors is what determines the flow rate.