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Old 03-03-2011, 06:13 PM   #1
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Default Question about Fuel Pressure

I ended up just picking up a clean set of Toyota 315CC injectors (green tops) + new seals (since my stock injectors were leaking at the o-rings anyways). I'm in the process of trying to adjust my BEGI AFPR. The first adjustment should be cake by setting it to 50psi @ zero point (aka: base). The second adjustment requires an adjustment on full boost. I've read for hours on boards and can't seem to determine the settings I should go with.

Here's my current setup:
- Greddy Turbo @ 6psi
- Starion FMIC
- Walbro 190 HP Fuel Pump
- K&N Filter
- Clutchnet 6-puck Clutch
- Stock injectors

These are my current # (bought the car with these settings):
37.5psi fuel @ idle
37.5psi fuel @ 0psi (Base point)
75psi fuel @ 6psi boost

Ideal settings:
43psi fuel @ idle
50psi fuel @ 0psi (Base point)
98psi fuel @ 8psi boost*

*I heard that a good rule of thumb is 6psi fuel pressure per 1psi boost, so...
50psi base + (6 x 8psi) = 98psi

However, the new injectors are more free flowing (roughly 37% more flow) since 230cc -> 315cc = 37% increase

My calculation @ full boost (8psi)
50psi base + (6 x 8psi) = 98psi - (98psi x .37) = 61.74psi

Should I go with the "6psi fuel to 1psi boost" rule or should be running lower fuel pressure due to running bigger injectors? I'd imagine that I would need less pressure with bigger injectors. Should I rely on my calculation of 61.74psi or go with the 98psi recommendation? Any thoughts? Unfortunately I don't have a wide-band A/F gauge or EMS (maybe down the line).
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Old 03-03-2011, 10:29 PM   #2
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Wide band. Then experiment. Not down the line, now.
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Old 03-04-2011, 02:06 AM   #3
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Definitely going wide band soon, but I have an AutoX event this weekend and I'm not sure running leaky injectors is a good idea ;P Any suggestions on fuel pressure in the meantime?
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Old 03-04-2011, 04:23 AM   #4
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Since you are running 315's, I would leave the settings where they are for the autocross.

This is based on a very old set up that I ran with 1.8 injectors at 80psi which was slightly on the rich side at 8psi.

Definitely get yourself a wideband. There are too many variables in your system to be shooting in the dark.
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Old 03-04-2011, 07:39 AM   #5
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if you see 38psi at 0psi, your oem FPR is broke.
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