Okay, i read "maiximum boost" (answered 99% of my questions) but im still lost on the FMU thing!

1. Do i need to run a return line to the fuel tank?
2. How is the FMU run? ie: line off test port to FMU then return line off FMU to tank?
3. slightly off topic; with 30lb injetors and walbro 255 pump, what should my static fuel pressure be running 7lb boost? I will be using the 8:1 FMU disk
i know about corbins fuel stuff, but im still stuck in the math of it all. Help a bruthu out...
tim

Don't feel bad man, I'm building a new motor outside the car as we speak and I'm still trying to get the fuel straight.

But a way I've been told to do it, is take the amout of HP you want your car to end up with (yes motor HP), then multiply it by .45, then divide that number that you get by 4 (for 4 cyclinders). IE I want my car somewhere near 400hp, so when I do the math it tells me to use 440cc injectors. Hope it helps!

>1. Do i need to run a return line to the fuel tank?

yes, unless you're a 95

>2. How is the FMU run? ie: line off test port to FMU then
>return line off FMU to tank?

correct, run a line from the test port to fmu in(i'm assuming it's similar to the sfmu) and then a return line connected to the oulet port.

>3. slightly off topic; with 30lb injetors and walbro 255 pump,
>what should my static fuel pressure be running 7lb boost? I
>will be using the 8:1 FMU disk

static should be approx. 30psi. idle should be 20-22psi.

well shit, i thought static was at idle. Okay, so what does "static fuel pressure" mean? how does that compare to fuel pres. at idle?
thanks guys

static is when the signal to the fpr is at 0, or atmospheric pressure. This would be equal to removing the signal line from the fpr or when your boost gauge is at 0. I dont think your fpr is adjustible other than changing the disk, so i dont know what to tell you. hope that helps tho!

sorry i forgot that w/ the regular fmu the stock regulator handles the idle fp. maybe someone w/ a reg fmu can help you on that one b/c you will have to adjust your idle fp's somehow when running 30# injects. anyway, yeah, like etx said, idle is at full vac(car idling) and static is at 0 psi(car off, fuel system pressurized).

Gotcha!!! i kind thought that was the difference. thanks.

no prob

IMO, you dont want to run the 30 lb injects with the stock FPR and the FMU. You dont have any way to lower your idle fuel pressure that way, as you need to when you run the larger injectors. I highly suggest you get the SFMU, as you can have FULL adjustability of your fuel pressures, both idle and boost. OR, just run the stock injectors, which will be sufficient to run 6-7 psi boost since you only have the 255 LPH intank fuel pump( it doenst like to flow well over 100 psi fuel pressure, as you need about 110 psi of fuel for 8 psi boost). You could also use the SAFC and the FMU with the 30 lbers,as the SAFC can help you lean the fuel out using the stock fuel pressures. But i dont like how it can advance your ign timing either under boost, soooo...

If you're dead set on using the FMU(in other words you don't want to buy a SFMU), then you could probably just get away with replacing the stock fpr with an adjustable one. Erik was talking about doing it - http://forums.2gnt.com/dcboard.php?az=show_topic&forum=8&topic_id=45174&mesg_id=45174&page=3


95 Eclipse RS : 5 speed
Jeep TB writeup - http://www.dimensia.com:81/jimbo/JeepTBfor2gnt.html

Thanks for everything so far guys, but this fuel system set-up stuff is really kicking me in the nuts and im not sure if im making it more difficult than it has to be....
Is there a DEFINITIVE source/place to go/"anyone willing to give me the A-Z steps" on what i need to do to get the correct fuel set-up for my t-25, 30lbs injectors, intercooled, 5-9(max) psi boost, turbo set-up?

I thought you had to get rid of your factory FPR when using a FMU, but now i read you dont. do you need an aftermarket FPR and FMU, or is that what essentialy an SFMU is. does a rising rate FPR replace the factory one and eliminate the need for a FMU also, or what???
will all my freaking fuel problems be solved with an SFMU? and if so, do i keep or get rid of the stock FPR?

Sorry guys if this is elementry stuff and im not gettting it cause im making it rocket science, please bear with me, when it clicks, it will click good!!!

A regulator "regulates" the fuel pressure in the system. The stock fpr is not adjustable, it's set to 50 or something like that and you can't change what it's set to. Some aftermarket regulators are adjustable - so you can control what the base fuel pressure is for the system.

A riser "rises" the fuel based on a boost feed. It rises it from a "static" fuel pressure at a calibrated rate. There are all kinds of disks/springs/valves involved, but basically the whole point is to raise the pressure a specific amount for each pound of boost. This ratio is referred to as the rising rate - increase fp by X per pound of boost.

So what you want to do is figure out what your static fuel pressure should be and what rising rate to use. The static fuel pressure is pretty easy, you want to pump out as much fuel as the stockers did on stock fuel pressure. For 30lb'ers, thats gonna be somewhere around 25-30 psi, let's set it to 28. Then to figure out the rising rate, you want to estimate how much crank HP you think you'll be generating at maximum boost. So in this case, let's say that you'll be making 230 at 9 pounds, allright? If that's the case, then you want to end up somewhere around 70psi fuel pressure at 9 pounds of boost. Time to calibrate the riser, the rate should be (max fp - static fp) / max boost or in this case (70 - 28) / 9. Comes out to 4.6. So my guess is to set the static pressure to 28 and rise it to 70 at 9 pounds of boost(4.6:1 rising rate).

You're going to have to decide how to do it first though.

The FMU is only a riser. The return line on it would go to the fpr, because in order to use it you still need a regulator. The problem is that you can't really use you're stock fpr with the FMU, because you can't adjust the fuel pressure with it. It needs to be set to 28 psi for the 30lb'ers. You would need to get an adjustable fpr. Depending on what kind of adjustable regulator you get, you'll at the very least be able to set the static fuel pressure to whatever you want. It may not be the most elegant solution, but it'll work.

The SFMU is a riser and an adjustable regulator all in one. The return line on it would go straight to the tank and you could ditch your stock fpr. The SFMU looks like a really good unit and it has some very nice features to really dial in a good tune. For instance you can set the "idle" fuel pressure, which is is the fuel pressure under vaccuum(while your not boosting). This is nice cause if your car boosts great with the static pressure at 28psi, but it idles like shit at that same pressure, then you can turn it down a bit for when you're not boosting. There are other things nice about it. Alot of people on the board really like it. I'm sure someone could tell you the exact disk/spring/idle fp/static fp that they run on thier SFMU with thier 30lb'ers. If for no other reason then that, I would sugguest that you consider getting one.


95 Eclipse RS : 5 speed
Jeep TB writeup - http://www.dimensia.com:81/jimbo/JeepTBfor2gnt.html

metaljim, you rock!!!!!!Thank you! i think i will ditch the FMU and go for a SFMU!!!!

I would PM XtremeRS and ask him how he set up his sfmu with 30# injectors. He can tell you exactly what static fp to start with and what disk and spring combo to use with the sfmu.

Also, when you buy the sfmu, you should consider buying the optional bleed valve with it as well. What that does is help you fine tune your wide open throttle fuel pressure. For instance, say that you figured out that you need 75 psi of fuel pressure at WOT and are trying to decide between two different calibration disks to use in the sfmu. One will raise your fuel pressure to 80 psi at WOT, and the other will raise it to 70 psi. The bleed valve would allow you to use the disk that raises your fp to 80 psi, but by bleeding off boost pressure at the regulator, you can obtain 75 psi at WOT instead of 80.

This bleed valve comes with the cartech regulator that HRC sells as well. I would imagine that many people around here still have their HRC regulator sitting in their garage and would take that valve off and send it to you cheap.

When everyone says 30lb injectors what is that in CC because I will be using 310cc injectors since Im looking at getting around 300hp in motor and doing the formula says 308 actually but 310 is close enough. So what is lbs to cc?