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Old 09-27-2011, 01:12 PM   #1
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Default RX-8 195500-4450 required fuel and max whp?

My MS2 is running my stock '99 fuel injectors right now. I use 13.2 for the required fuel. I had a set of RX-7 460's a while ago, and was running 6.9 for the required fuel.
What should that number be for the RX8 425's?
I am am running my stock '99 returnless fuel system with a walbro 255 fuel pump. With my current fuel setup and the RX8 425's, what whp would max out these injectors?
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Old 09-27-2011, 01:35 PM   #2
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if you went from 13.2 to 6.9, that assumes your injectors were 52.3% larger.

since 6.9 is 52.3% of 13.2. So that means you were assuming your stock ones are 240cc.

so:

240 / 440 = 54.54

13.2 * .54 = 7.2


or

440 / 460 = .9565

so 6.9 * 1.0435 = 7.2
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Old 09-27-2011, 02:02 PM   #3
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Awesome. Thanks! How much hp do you think these injectors can support?
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Old 09-27-2011, 02:08 PM   #4
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~240
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Old 09-27-2011, 02:18 PM   #5
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Quote:
Originally Posted by Braineack View Post
~240
That's all? Even at my current fuel pressure? I was hoping for more like 270ish whp.
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Old 09-27-2011, 04:48 PM   #6
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FWIW, I run req fuel of 8 with them.
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Old 09-27-2011, 04:58 PM   #7
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Quote:
Originally Posted by thirdgen View Post
That's all? Even at my current fuel pressure? I was hoping for more like 270ish whp.
assuming you can hold 60psi to redline, then I think that will be pushing it.

If I run 15psi, I'm technically running more fuel pressure than you, due to my 1:1 fpr.

I'm around 50psi before I hit boost, so if I add 15psi, the fuel pressure is at 65psi. But the extra fueling only equalizes the pressure in the intake. So lets call it 50psi.

The more you add boost, the less capacity your injectors ultimately have. for every 1psi of boost, you're lowering the capacity by another 1psi. At 15psi, you're fueling like you only have 45psi in the rail since there's no compenstate for the atmosphere in the intake.
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Old 09-27-2011, 06:33 PM   #8
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What kind of FPR are you running?
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Old 09-27-2011, 06:39 PM   #9
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stock...
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Old 09-27-2011, 06:51 PM   #10
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So pretty much my SR20 turbo at like 15 psi will most likely max out these injectors?
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Old 09-27-2011, 08:22 PM   #11
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(Posting from my phone.)

Well the turbo will never hit 270rwhp so ur okay...
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Old 09-27-2011, 10:08 PM   #12
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I know that, I've never seen anybody make more than 240whp with that turbo. I'm thinging about running a Godspeed 3076 with low boost. I also noticed you listed those injectors as 440's, but they're 425's. So my required fuel should be higher than 7.2, but I'm not sure how you got that number to multiply to the old required fuel number.
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Old 10-01-2011, 09:07 PM   #13
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The actual number isn't that important. It's just a multiplier. Just make sure the values in your VE table are reasonable (not too low). The higher the values, the more accuracy. Say you have 100 in a cell and you change by 1, that would give you 1% resolution. However, if you have 200 in a cell, you have 0.5% resolution. Keep in mind that the max value is 255 though
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Old 10-01-2011, 11:55 PM   #14
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I understand. I just remember that when I swapped in 460's (which was done like 4 times back and forth) I changed 13.2 to 6.9 and I barely had to adjust my fueling. I calculated that with the RX8 425's, 7.45 is the number I will need.
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