Question about Fuel Pressure - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to   Members

ECUs and Tuning Discuss Engine Management, Tuning, & Programming

LinkBack Thread Tools Search this Thread
Old 03-03-2011, 07:13 PM   #1
Thread Starter
Join Date: Nov 2007
Posts: 13
Total Cats: 0
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).
supahamster is offline   Reply With Quote
Old 03-03-2011, 11:29 PM   #2
Elite Member
iTrader: (24)
kotomile's Avatar
Join Date: Oct 2006
Location: Monterey, CA
Posts: 7,578
Total Cats: 40

Wide band. Then experiment. Not down the line, now.
kotomile is offline   Reply With Quote
Old 03-04-2011, 03:06 AM   #3
Thread Starter
Join Date: Nov 2007
Posts: 13
Total Cats: 0

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?
supahamster is offline   Reply With Quote
Old 03-04-2011, 05:23 AM   #4
AFM Crusader
iTrader: (18)
olderguy's Avatar
Join Date: Oct 2004
Location: Wayne, NJ
Posts: 4,438
Total Cats: 84

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.
olderguy is offline   Reply With Quote
Old 03-04-2011, 08:39 AM   #5
Boost Czar
iTrader: (61)
Braineack's Avatar
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,819
Total Cats: 1,780

if you see 38psi at 0psi, your oem FPR is broke.
Braineack is online now   Reply With Quote

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 57 07-19-2017 05:11 PM
OTS Bilstein to motorsports ASN conversion stoves Suspension, Brakes, Drivetrain 5 04-21-2016 04:00 PM
Walbro 255lph Fuel Pump $50 lsc224 Miata parts for sale/trade 2 10-01-2015 10:17 AM
Low oil pressure after 1.8 swap and new turbo setup JesseTheNoob DIY Turbo Discussion 15 09-30-2015 03:44 PM

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

All times are GMT -4. The time now is 01:32 PM.