pushing WRX 440cc's to the limit

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yellerandahalf

Member

:

'03.5 MSP(Yellow!)

• Nov 30, 2005

• #1

Ok y'all, I've been doing some calculations on fuel delivery to investigate why I'm hitting 100% duty cycle at 6500rpm. I've figured out that I only need like a 150lph fuel pump to achieve 350bhp, so that's not it. I took a look at what my calculated injector size would be for this app, and found it to be 63#/hr! the WRX's are only ~42#/hr! so that's it. now, I'm not near 350bhp yet, so I don't need quite that much, but i will. Anyways, injector flow rates are calculated at standard fuel pressure, 3 bar (about 44.1psi). Now, it is common practice to increase fuel pressure to compensate for the size of your injector's virtual penis. assuming a completely linear increase in flow rate due to pressure, 4-bar would give me 580cc/min at 4 bar(58.8psi). The generally-accepted max pressure injectors can handle is 70psi, so I'm nowhere near that. but can the rail and fittings be pushed that hard? does anyone know? Also, does anyone have any data on how the WRX injectors react to pressure increase? perhaps a curve? that would be awesome. also, those of you who have put in adjustable pressure regulators and such, where did you run your fuel lines to? I have several -6AN fittings, and lots of -6 line to work with. Thanks for your help!
-Mateo

 

R

Rainman

Member

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2006 Black Mica MS6 GT + 2007 MS3 (2003.5 Yellow MSP = retired)

• Nov 30, 2005

• #2

don't know, but subscribing so that I can learn something.

R

 

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yellerandahalf

Member

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'03.5 MSP(Yellow!)

• Dec 1, 2005

• #3

haha wee! i wonder if subaru might have this kind of info? anybody have connections with the subaru forums?

 

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Jeph

Member

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2002 ES-T (dead)

• Dec 1, 2005

• #4

You could just go register, or browse the nasioc forum, and i bet you'd find your answer

 

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peepsalot

Member

Contributor

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Black 03 MSP

• Dec 1, 2005

• #5

injector flow rate with increased pressure is not a linear function. It is something more like flow rate is directly proportional to the square root of the fuel pressure. I have a book that gives a general equation for it. I can post it up when I get home.

 

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peepsalot

Member

Contributor

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Black 03 MSP

• Dec 1, 2005

• #6

To find the new FUEL FLOW rate after a fuel pressure change:

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</CENTER>http://www.rceng.com/technical.htm

 

C

CWiLL

Member

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2003 Mazda Protege 5, silver

• Dec 1, 2005

• #7

are u running the injectors now? y dont u just turn the boost up till u run out and stop calculating

 

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daedalus

Member

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BANANA OF FURY

• Dec 1, 2005

• #8

if you've got the blue subbie injectors you can cut them to flow somthing crasy like 880cc's. Search on NAISOC for the thread.

otherwise, i think the sti 550's fit in as well..

 

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lcruz64

Member

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03 MSP

• Dec 1, 2005

• #9

Subaru WRX Modified and Matched 800cc injectors
https://www.ebay.com (commissions earned)

 

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yellerandahalf

Member

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'03.5 MSP(Yellow!)

• Dec 1, 2005

• #10

wow that's really friggin expensive! that's DEFINETLY not worth the sevice provided. damn. many thanks for that equation! it's just what I needed. now to install the regulator. Any thoughts on where to tap into the fuel system to include the regulator.

 

J

Jeph

Member

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2002 ES-T (dead)

• Dec 2, 2005

• #11

OH YEAH! I did read that you can make the blue wrx injectors flow a lot more. There was a whole thread about it here too a long while back.

 

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wicked

Member

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2003.5msp

• Dec 2, 2005

• #12

your MS has extra injector driver doesn't it?
consider a secondaries rail.

 

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yellerandahalf

Member

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'03.5 MSP(Yellow!)

• Dec 2, 2005

• #13

nope, primaries only, by default. I could possibly wire it up to run secondaries, but it wouldn't be worth my while. Plus it'd be much easier to tune with just bigger flow rates.
-Mateo

 

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DiscreetSpeed

Member

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03 MSP

• Dec 2, 2005

• #14

eh there is something about the sti pink 550's that are not compatible on our cars...i dont remember off the top...ill find out.

 

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LinuxRacr

Contributor

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2001 Mazda MP3

• Dec 2, 2005

• #15

I think the fact that they are side-feed or something like that..

 

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yellerandahalf

Member

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'03.5 MSP(Yellow!)

• Dec 2, 2005

• #16

hmm interesting. I'm probably not going to go with the 550's unless I need to. I'd rather adjust my fuel pressure. They are an option though. I thought maybe the electrical clips don't work? maybe that was it?
-Mateo

 

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igdrasil

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12psi Protege5

• Dec 2, 2005

• #17

yellerandahalf said:

hmm interesting. I'm probably not going to go with the 550's unless I need to. I'd rather adjust my fuel pressure. They are an option though. I thought maybe the electrical clips don't work? maybe that was it?
-Mateo

Click to expand...

I have pushed over 120psi on the fuel rail with no problems on stock injectors. Using the MSD HP Fuel Pump and a Vortech 12:1 @ 11psi of boost.

I ran 10psi for over a year without issues.

 

Y

yellerandahalf

Member

:

'03.5 MSP(Yellow!)

• Dec 2, 2005

• #18

oooo i like it! do you know whether or not the subaru injectors are going to withstand that much pressure as well?
-Mateo

 

V

Velocifero

Wham Bam thank you Ma'am

:

VRM MS6, Sunlight Silver MSP

• Dec 2, 2005

• #19

subscribing b/c i just traded parts for a set of wrx injectors and i need to know more about it, thanks for the info so far guys

 

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igdrasil

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12psi Protege5

• Dec 3, 2005

• #20

hoestly I dont know, I had them on my car and it was a pain to tune them with stock ecu.