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!

[WannabeGT4]

An FMU (Fuel Management Unit) is pretty much just an additional fuel pressure regulator... It is generally installed after the stock FPR in order to raise the fuel pressure beyond the stock setting.

The numbers 8:1, 10:1, 12:1, etc are just ratios of the amount of fuel pressure increase per pouud of boost. For example with a 12:1 FMU your fuel pressure will raise 12psi for every one psi of boost.

Using an FMU is the simple and basic way of increasing fuel output through the stock injector for forced induction applications. The more accurate way would be to use oversized injectors and either a piggyback fuel computer or a standalone ECU. This will result in a more precise and reliable tune.

Also worth noting is the relationship of fuel pressure to flow rate when it applies to fuel pumps. As the pressure rises the amount of fuel that can flow over a given amount of time will decrease. That's just one more variable that you have to worry about when you're working with an FMU as opposed to a set fuel pressure and proper tuning.

This post has been edited by WannabeGT4: Jun 22, 2006 - 3:19 PM