Why FMU's suck
 

I could do a search and find out but I was talking to my friend who has done a bunch of turbo setups on his friend's cars before and said the FMU's were good and could be run beyond 6 psi (I told him they couldn't handle past 6 psi) I knew they sucked but he seemed to know more about it so I ended up looking stupid and he successfully defended the abominations that are FMU's. If somebody could give me the top 5 reasons FMU's suck that would be great.

Re:Why FMU's suck
 

they make the fuel pressure too high once you start boosting more...which isnt good

Re:Why FMU's suck
 

if they malfunction, your motor blows up. what more of a reason do you need???

Re:Why FMU's suck
 

ok heres and even better reason. as fuel pressure goes up fuel delivery volume from your pump goes down. IE

at 45psi a pump delivers 125lph
at 55psi same pump now delivers 00lph
at 65 psi same pump is now at 85lph
at 75 psi same pump is now at 40 lph.

not really a good situation. Also these are dead head pressures not accounting for boost. and are not actual nubers. they serve only as an example. but typically for every 5 psi in pressure increase pumnp volume drops 10% so if you increase pressure with and fmu say 15 psi youve lost 30% of you pump volume. its not a perfectly linear thing but it gets progressively worse as pressure goes up. IE at 5psi increae its 10% but at a 10 psi increase its more like 20 % and that is the real reason why fmu's suck.

Re:Why FMU's suck
 

Uhhhh thats why you upgrade your fuel pump buddy.

Re:Why FMU's suck
 

lack of tunabilty.....bottom line

Re:Why FMU's suck
 

Well... I run FMU 10:1 disc with inline fuel pump.
So far.. me happy.
But, here are pros/cons for an FMU:

Pros: you'll easier pass smog test, whilst not in boost car drives like stock - idles like stock and accelerates, etc... no sputterings... usually cheaper than AFC+injectors; it works

Cons: high fuel pressures (you *do* need inline fuel pump), hard to tune (only by changing discs), not good for higher pressures due to rising fuel pressure

Overall... as said, I have FMU with inline pump. According to A/F gauge I'm rich all the way with 10:1, even when boost creeps up at 8psi (it's set to 7 psi).
People who say FMU is not 'adjustable'... it is, by changing discs... either buy 'em, or make yr own. Yes, you actually *can* do that! Imagine that...
This mostly goes to those who were running pig rich by using 12:1.. why not use 10:1, or even 8:1 if you were running *that* much rich?

Re:Why FMU's suck
 

Exactly. Sure, you can change a disk, but how good of a tune is that? I'd like to see how fucked up the A/F is across the RPM range with an FMU. :-X
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Re:Why FMU's suck
 

boost transition sux

Re:Why FMU's suck
 

What boost transition?!

Re:Why FMU's suck
 

I didn't know that just by changing discs your entire powerband will be self tuned to a perfect A/F ratio. ---- I wasted all this money on an EMS when all I needed was a rubber disc. ::)

Bottom line is this type of ghetto fuel management is for amatures. Fuel management is controlling injectors to tune your entire rpm band not run 350psi of fuel pressure to just dump shitloads of fuel. You not getting maximum power doing this and its just stupid.

FMU's became popular becuase its the cheapest fuel management and people pay $3000 for turbo kits and these things come with it so everybody just assumes that they are acceptable becuase Drag or Rev Hard say so.

Re:Why FMU's suck
 

fmu's are a bandaid, not the fix. They are widely accepted, because of the ease of installation. Getting the right sized injectors, and a programmable fuel injection, is the right way to go about it..

But, Building an engine for boost, and getting the right sized turbo is also the way to go. Instead people are boosting 100,000mi engines, in stock form, and putting a turbo they got out of a junkyard on.

You can put on an FMU if you want to. Or, you can chip your computer.. which will be more involved, but better in the long run.

Re:Why FMU's suck
 

What if you buy say the greddy kit for the civic ex, it comes with the emange fmu, when im ready to go into say 10 psi, i think this is what id need to do,

get rid of fmu, get safccII,upgrade the whole damn fuel system, is that right ?

sry to be stupid i need this answered before i drop a few biguns on turbo stuff.

Re:Why FMU's suck
 

Don't buy the greddy kit. Build a kit for cheaper and don't even bother with the FMU. Do it right from the beginning.

Re:Why FMU's suck
 

so, who cares? not everyone has the money for an all-out setup

Re:Why FMU's suck
 

you cant tune an fmu. even changing the disks, isn't tuning.

fmu = when there's nothing else or simple solution.

Re:Why FMU's suck
 

FMU is perfectly fine for low boost (8psi or less) . If you are running more than that than i would suggest better fuel management. I have been running a 12:1 FMU and inline fuel pump for almost 4 years now. No problems, and no complaints.

Re:Why FMU's suck
 

Seriously, what is the big deal about using an fmu when the person wanting it is only going to boost 5-6 psi. Yes you can be more efficent with vafc or te and some dyno time.

A fmu with a low psi turbo is going to be better than turbo & no fmu, or no turbo at all. Just don't expect it to cya at 8+ psi.

Re:Why FMU's suck
 

i'll bet alot of people would be suprized about how much more power a car @ 8psi, a safc, some 440s and a little dyno time can make, compared to the same car, with the same setup and a fmu.