07-25-2007, 09:12 AM
Join Date: May 2005
Location: Chantilly, VA
Total Cats: 1,358
4 High pressure fuel pump
The stock Miata fuel pump can only provide so much fuel (tends to max out around 85psi).
...So you need to upgrade the pump if you plan to fuel past 70-80psi; usualy due to running small injectors on an FMU setup.
...the fuel pressure raises the size of the injectors.
Other than that, you don't need one. If you have an aftermarket ECU, the stock pump more than enough at 50psi.
For the longest time the Walbro 255 lb/h fuel pump had been the accepted pump for FI Miatas. The 255 flows more fuel at any giving pressure level than is needed. They tend to overload the OEM FPR and cause the system to run rich even in vacuum.
Instead of idling at 35psi and reaching 50psi at 0~hg. It will run closer to 40psi at idle and 55psi at 0~hg.
The ideal pump is the Walbro 190 lb/h HP fuel pump.
...It is important you get a HP unit if you plan on raising the fuel pressure levels past 90psi.
...The 190 HP unit will not only supply four 700cc injectors with enough flow to maintain 40-50psi in the fuel rail (enough for 400hp), but out flows the 255 HP model after 100psi.
TURBO MIATA FAQ