Fuel pressure increase while in boost ( question )
 

I had this idea cross my mind this weekend when messing around to change the injector orings ( leaking under boost ) .
Here is my car b4 going further:
3" Exhaust with High flow cat
open intake
intercooler upgrade ( pettit medium style )
2 manual boost controllers ( 1 WG and 1 PreC.)
pettit unlimited ecu
stock fuel system
no more FPD ,
fuel pump rewired to get full voltage on stage 2 ( WOT )
fuel filter relocated to engine bay ( will fuel temp affect anything??? )
and a bunch of other non air flow relevant things things
boost <= 1 bar


what if instead of feeding the fuel pressure regulator from the LIM .. i feed it from the pre intercooler turbo nipples with the goal of slightly increasing the fuel pressure ... there might be 1-2 PSI more pre intercooler , so 1-2 psi more fuel pressure

what are your thoughts ? what would be the effects of 1-2-...5 psi more under boost

thx

I'm pretty sure that the regulator doesn't increase when pressure is increased. It only decreases when vacuum increases. When no vacuum is present or pressure is, the regulator is just at a base pressure.

some one correct me if i'm wrong

At atmospheric pressure, an FPR is at its "base" pressure. Apply vacuum to it and it will reduce fuel pressure. Apply boost to it and it will increase fuel pressure. On normal FPR's, this is usually at a linear rate-- so 1 psi of boost in the manifold will result in base fuel pressure + 1psi . If your FPR is seeing higher pressure than the manifold, it would run richer and probably lose power, unless it was too lean in the first place.

Yea, i thought the FPR was there to regulate pressure, and adding more would affect nothing since the regulator is already doig it's job...hmm...

It's not a good idea to increase the pressure without doing some wideband testing. If you really wanted to do this, just get a RRFPR (Rising Rate FPR). At least it will be predictable for the behavior of the fuel pressure. This was one of the ways used to increase fuel before standalone ECU's where available.

i was thinking to do this to be more "safe" while boosting at the limit of the system ( 1bar )

i have a friend here who i bought an ecu ( pettit unlimited ) from and he checked with a wide band o2 the gases coming out of a similar setup (~100xxx km`s , intake , inter cooler. exhaust ~ 15-16 psi ) and it was in the 11.x range pre cat on stock fuel system without fuel pump rewire ,
now i dont want to run over 1 bar , just up too one bar ,

The only way to know is to put a wideband on it and see what the AFR's are, just blindly increasing fuel pressure or adding fuel is not the way to tune. The stock FPR is a rising rate regulator. 1:1, so as boost goes up it increases fuel pressure the same amount. The stock regulator is fixed though so the base pressure can't be adjusted. If you put the vacuum source on the pre intercooler vacuum nipples then you won't get vacuum at the fpr and your idle will be too rich, this is not a good way to do it. Leave it where it is and check your AFR's, if you need more fuel then there are much better ways to do this. Any increase in fuel pressure is going to make the whole map richer and power will fall off, which might be okay if you are definitely overly lean.

damn i did not consider the lack of vacuum pre throttle body , your right ,
in nay case it was something i needed to discuss with you guys ,
thx for the input :)

I agree with this. I've got my fuel pressure displayed inside my cabin (right next to the AFR gauge) and see the rise and fall every day I drive my 7.

Increasing the base fuel pressure (by using an aftermarket FPR such as Aeromotive) will let you get more boost capability out of smaller injectors (an increase of 10psi to the base pressure will make 850cc injectors flow at the rate of 1000cc's), however it's NOT a good idea to experiment with this unless you're a professional and really know what you're doing.



If I were you then I would look into upgrading your fuel system (not just re-wiring the pump) if you want to run 1 bar of boost. IIRC I was maxing out (100% IDC) my stock injectors at 13psi of boost. I'm currently hitting right about 85% IDC at 18-19psi of boost (1.3bar) while running 4x 850cc injectors at a base fuel pressure of 50psi. That is about the limit for "smart" before you're looking at running into more problems then the gains are worth.

can the pettit ecu be reprogrammed to accept 850`s overall ?

Unfortunately I don't know much about the Pettit ECU. It's just a piggyback to change the fuel maps/timing on the stock ECU, is it not?

If you're looking to do some serious modifying than I'd just bite the bullet and get a fully tunable ECU (PFC, MoTeC, Haltech, etc).

Yes and no. Yes it could, it just has a map on it like any other ECU for the FD. However, I don't know who you could get to program it. Shops like Knight Sports and Re Amemiya sell rechipped ECU's which are programmed as such. Pettit looked into providing a rechipped ECU for larger injectors, but I don't think they saw the need for it since the PFC had come down in price over the years.

can a mod delete this post and the one i made earlier. Thanks

you can not run 1 bar on boost on the stock injectors, you are going to be too short. And you can't upgrade the injectors with the pettit ecu. So either buy a Power FC and change the injectors or just limit your boost to 12 PSI.

Told you...