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]

Manny, Thanks again for your enlightening answers. I learn so much from reading your words. Initially I am hoping to just build a reliable 5SFTE that puts out 2/3's the power of yours (of course I would like to equal you! ). Initially I am more interested in understanding the 6GC engine and learn how to do some minor tuning (on a dyno of course!). Perhaps down the road, once I have the knowledge you have built up I can look into finer tuning and a better setup, but for now you are just going to have to put up with me asking you questions and copying you for the most part!

One question I do have for you about the emanage. Is it as easy to do minor tuning (ie. fuel only, such as the SAFC) or is it very advanced and in depth? I would look into getting it, as long as it isn't rocket science just to adjust fuel flow. So are you able to adjust the fuel flow with it and still have the timing remain the same, or do you need to adjust the timing to compensate for the fuel adjustments in emanage? I know that you are just running the SAFC right now and have removed your MSD, if I were to go that route would you suggest just the SAFC or would you suggest I get the MSD as well?

Another question for anyone to answer is still relating to the pressure vs boost. Anybody know what relationship of fuel system pressure to the boost pressure? Is it a 1:1 setup or is it quite a bit more? Also what is the stock fuel pressure in a 5S?

[phattyduck]

Another question for anyone to answer is still relating to the pressure vs boost. Anybody know what relationship of fuel system pressure to the boost pressure? Is it a 1:1 setup or is it quite a bit more? Also what is the stock fuel pressure in a 5S?

Generally, stock setups have a 1:1 FPR. This allow the pressure differential betweent the fuel and the intake manifold (where the injector lives) is the same at all times. For most cars, this is somewhere near 40psi. The idea behind this is to keep the amount of fuel that flows out of the injector for a given time period the same under all operating conditions.

This sometimes breaks down for stock N/A cars after they are turboed if the stock FPR cannot keep up (either with the fuel flow of a high flow pump, or the boost pressure not causing a rise in fuel pressure). This is a possible concern on aftermarket turbo kits, but it doesn't seem to be a problem on the 5s (somebody correct me here if I'm wrong! I've only worked on the 3s-fe and stock turbo cars).

-Charlie