FMU's, Are they needed? Options

[WALKER]

Alright, so this will probably sound like a very dumb question to those of you that are experienced turbo people, but basically what is an FMU?

I am new to the world of turbos and am slowly building up my knowledge so that I can build a turbo on my 5S. My research has brought me to the point of FMU's (fuel management unit, I am assuming). People everywhere on other sites are talking about them and FMU ratios of 4:1, 6:1, 8:1, 10:1, 12:1, etc. Well this is the first I have heard of FMU's and by conducting a search on 6gc it looks like there are some comments about them from a ways back, mostly just asking about what ratios to use. Basically what I have been able to figure out is it was used in the past by some 6GC's to push the stock injectors and fuel system...is this correct?

From what I have read recently about the 5SFTE there is no mention of FMU's, so are they needed? Basically all I have read about requirements of the fuel system for a turbo 5S is to get the 460cc injectors and a Walbro 255 fuel pump (or similar) and use either a SAFC2 or eManage.

I am hoping some of you with experience can clarify this for me. Also if you could explain exactly what an FMU is and how it works and what do the ratios mean? Does a standard fuel system have an FMU ratio?

Thanks in advance for your help!

[presure2]

wannabegt4 did a great job of explaining the fmu.
you have the right idea.
its IMO a very dangerous way of increasing the available fuel you have.
with the 2 bar map sensor, and larger injectors, it works like this:
the stock map sensor only reads vacume.
0 volts = 100% vac (these are not exact #, this is just to give you the idea of how it works)
5 volts = 0% vac (WOT)
now a 2 bar map sensor works the same way, only 0volts is 100% vac, and 5 volts is +14.7psi
the ecu uses the map sensor voltage, along with the other sensors in the engine (TPS, IAT, Coolant temp ect) and determines the amount of fuel to inject.
so, becuase the stock injectors are ~220cc, if we use injectors around 440cc or so, we end up with double the fuel.
the SAFCII intercepts the signal going to the ecu, and tricks it into thinking there is more or less air going into the engine(depending on weather you add or remove fuel) which in turn affects the amount of fuel the ECU injects.
the drawback of the SAFCII is that by tricking the ecu about the amount of airflow, that affects how the ecu applies timing to the engine, so, i personally dont like to make big adjustments with it. i think of it as a fine tuning thing.
the emanage ultimate is a better option, because with it, you can adjust fuel flow independantly of timing.
it can adjust fuel in the same manner as the SAFC, or you can adjust it by controlling the injector opening time.
you can also adjust timing, which IMO will really open the door so to speak once we get an experienced tuner willing to take the time and tune it properly.

to be honest, i really still think the BEST setup on the 5sfe is still out there, waiting to be made.
with the stock ct-26, im thinking the 460's are a little big.
if we had more peope willing to try some stuff, id really like to see someone try a set of injectors like maybe 390cc or so.
that would give you enough fuel for ~235whp, and wouldnt be as rich as most of the guys are running now.
IMO there are 3 main keys in building a sucsessfull 5SFTE:
#1 start with a healthy motor.
#2 eliminate weak points in the setup (IE: oil and waterlines, IC piping ect..)
#3 (and prolly the most important, aside from starting with a good motor) TUNING.