doing some research

allensteiner21 · 09-04-2008, 03:25 PM

hi guys,
i've been thinking about going turbo since i got my max last year but i support my wife and our baby girl so money is a bit tight to go all out.
that's why i wanted to ask if anyone is using a FMU with a fixed ratio instead of a wideband setup? the fmu is a lot cheaper and i wouldn't have to spend money on emanage and dyno time to get my afr tuned. especially with a fixed 12:1 ratio seems pretty good and not too rich when just going to get groceries. can anyone give me their thoughts on that?

kzoosho · 09-04-2008, 05:11 PM

A fmu will not replace a wideband. They do 2 different things. The fmu controls your a/f via fp and the wideband tells you your ration of fuel to air. You can run a fmu but you want a wideband to make sure that it is actually doing its job.

allensteiner21 · 09-04-2008, 06:05 PM

thx kzoosho, i won't need a piggyback though, just a wideband and a gauge toknow for sure right?

one more thing. under boost should i try to keep it aroud 14, 15:1 like on na or is 12:1 fine? i've also seen 10:1 fmu's - that's too rich, isn't it?

**Nealoc187** · 09-04-2008, 06:09 PM

you're not understanding how the fuel system works.

A wideband is a monitoring device, you cannot make *any* changes with it. It is like your speedometer or gas gauge, it tells you the status of a parameter and that's it. It tells you what your air fuel ratio is.

An FMU is a device that raises your fuel pressure in order to get more fuel into your motor (to match the additional air being forced into your motor by the turbo or supercharger). The numbers you see associated with an FMU are not air fuel ratio numbers. They are the rising rate setting of the FMU. The vortech FMU for instance uses individual discs that you swap in order to change the rate at which your fuel pressure rises for every pound of boost. For instance a 6:1 disc will raise your fuel pressure 6psi for every 1psi of boost that you make. You still need to have some way to figure out what the resulting air fuel ratio would be - hence you would need to have a wideband (or at least borrow one or put your car on a dyno and use one there). The catch is that you don't want to get too aggressive with the FMU setting because really high fuel pressures mean increased likelyhood of fuel injector failure, which is a bad thing.

FMU is a crude tuning device, a device that you can make actual changes with. Wideband is a monitoring device, a device which you can only glean information from about the air fuel ratio that your fuel setup has you running.

allensteiner21 · 09-04-2008, 09:29 PM

that's a very good explanation, thanks. i thought an fmu keeps a steady afr...i guess it's not my best option then since it would put the fuel pressure through the roof under boost.
back to reading.

**Nealoc187** · 09-04-2008, 11:02 PM

Well it won't necessarily put the FP through the roof, but it will raise it some - depends on what disc you go with. If you are looking for a very basic FI setup it's OK to use an FMU so long as you don't jack the fuel pressure up too much, but for more advanced tuning and higher power levels you need to ditch it and go with properly sized injectors and a tuning device like an emanage.

*The Wizard* · 09-05-2008, 02:21 AM

Nothing but great advice in here.......

OP, definitely keep things basic (and fairly inexpensive) and go with the FMU for now. The wideband's companion is the AFC (or EMU once you go advanced). The AFC changes (tunes) the AFR, where as the wideband shows you the AFR.

I had my FMU and stock injectors forever and ever. Only once I was comfortable with FI and understood how things worked independently and how things worked together, did I choose to step it up a couple notches and go advanced. I then ditched my FMU, installed 555cc injectors, dropped pulley sizes, installed an Innovate Motorsports wideband, and installed the EMU.

allensteiner21 · 09-05-2008, 01:02 PM

i'm learning at accelerated speed here, thanks fellas. one more though. the fmu raises fuel pressure by a set amount to 1 psi of boost gained. so if i got a blower and not to push too hard - while still learning - ran about 8psi should i get a disc set at about 4 or 5(max?) :1? i've read somewhere that more or less 35 psi of fuel should be right - that's also what i kinda figured out from the graph in one of the stickies. i know it's more complicated than that but i couldn't find any packages with different disks so i could get close to "just right" by observing the afr gauge and changing disks.

*The Wizard* · 09-05-2008, 06:30 PM

Quote:

Originally Posted by allensteiner21

i'm learning at accelerated speed here, thanks fellas. one more though. the fmu raises fuel pressure by a set amount to 1 psi of boost gained. so if i got a blower and not to push too hard - while still learning - ran about 8psi should i get a disc set at about 4 or 5(max?) :1? i've read somewhere that more or less 35 psi of fuel should be right - that's also what i kinda figured out from the graph in one of the stickies. i know it's more complicated than that but i couldn't find any packages with different disks so i could get close to "just right" by observing the afr gauge and changing disks.

IMO, you'll be just fine with a 8:1 disc.

If you want different discs, they can be bought directly from Vortech at www.vortechengineering.com.

Of course, there's always ebay.

wewe447 · 09-15-2008, 07:23 PM

hi iam turboing my maxima and using a vortech fmu but dont no waht ratio will work with me i want to no if iam runing 6 to 8 psi what ration will work with stock injectors
thanx

96blkonblkse · 09-15-2008, 08:43 PM

Start with an 8:1 disk. Probably the safest bet.

A FMU needs to be used in conjunction with a Walbro 255 or the Vortech T-REX pump. The stock fuel pump isnt capable of puping out the fuel pressure required of the FMU.

Basically how a FMU works to the OP.

If you get an 8:1 Disk. For every 1PSI positive increase in manifold pressure, it will boost fuel pressure 8PSI. A 12:1 disk, 12PSI increase for every 1psi increase in maifold pressure. Id start with a 8:1 Disk. Its a good medium, from there on, once you dyno or get a wideband. If your terribly rich, move down to a 6:1, or pull fuel with a SAFC/Emanage.

A FMU Will never get you a perfect A/F on its own. As Neal said its a very crude tuning device. Its a bolt on tuning device. When combined with a SAFC or Emanage( i dont know why lol). It can get you a pretty flat AF. But you'd be best off with a AFPR, larger injectors, Walbro 255 and a Emanage Ultimate/Emanage Blue.