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!

[WALKER]

Thanks alot WannabeGT4. So basically what an FMU is a bad way to bypass using proper injectors, tuning, and fuel pump. That would be why it was looked at in the past before knowledge of what larger injectors and setup could be used.

Basically an FMU seems like a terrible idea then for any more than a few psi of boost since the stock fuel pumps could not handle it. It would even be challenging for a walbro to handle it if I understand correctly. If stock fuel pressure is 43psi, then with a 12:1 FMU @1psi need 55psi, @2psi need 67psi, @3psi need 79psi?

One thing I am still wondering about is if you just use larger injectors, what type of ratio is applied when boost. Is it a 1psi increase to the fuel system per 1psi of boost? I am just trying to plot out a graph to determine the fuel pressure requirements. I am assuming that the stock fuel pressure would be around 43psi, correct?

What type of impact does an SAFC have, I know you can add and cut fuel, but does that have any impact on the pressure?

[WannabeGT4]

Thanks alot WannabeGT4. So basically what an FMU is a bad way to bypass using proper injectors, tuning, and fuel pump. That would be why it was looked at in the past before knowledge of what larger injectors and setup could be used.

Basically an FMU seems like a terrible idea then for any more than a few psi of boost since the stock fuel pumps could not handle it. It would even be challenging for a walbro to handle it if I understand correctly. If stock fuel pressure is 43psi, then with a 12:1 FMU @1psi need 55psi, @2psi need 67psi, @3psi need 79psi?

One thing I am still wondering about is if you just use larger injectors, what type of ratio is applied when boost. Is it a 1psi increase to the fuel system per 1psi of boost? I am just trying to plot out a graph to determine the fuel pressure requirements. I am assuming that the stock fuel pressure would be around 43psi, correct?

What type of impact does an SAFC have, I know you can add and cut fuel, but does that have any impact on the pressure?

Well when you use upgraded injectors you swap the stock MAP sensor to a Turbo Pressure Sensor from an All-trac or MR2... That alone changes the way fuel is delivered at a given PIM output voltage to the ECU. You're in essence tricking the N/A ECU into fueling your engine like it was turboed. Obviously with all this trickery going on you need the SAFC to fine tune things and get them as close to normal as possible. The E-manage does quite a better job at this than the SAFC since it's a much more in depth tuning device.
Pressure2 should chime in any second here and go into more detail. He could probably explain the tuning side of things a lot better since he's been working with his for over a year now and studying the E-manage Ultimate for several months.