12:1 fmu @9psi??

[sunnys14]

i currently have a 12:1 vortech fmu disk... i have been reading that 12:1 is way too rich for your car and that a 8:1 is recommended for 8-9 psi of boost? anyone wanna help me out? should i keep the 12:1 or buy a 8:1 or 10:1?

[Checkered-Member]

LoL…ok…with a 12:1 FMU @ 9 psi means that on top of the stock 45psi stock fuel pressure you will add 108psi so 153psi fuel pressure…

Your fuel pump will blow …if notYour injectors can no longer open after 100psi or they blow ...if notAnd it will be hilarious if you blow the fuel rail at 153psi

So many things will blow before you go rich

Please don’t use FMU’s as fuel management, that’s like using a bottle opener to regap spark plugs…lol…

If I sound like an @$$ its only because its 1:20am…

[sunnys14]

if 12:1 is bad then why would boost designs sell it on their stage 1 kit? youre saying that a 12:1 disk wouldnt work at all?

[Craving4Boost]

sigh we've heard so many of BD excuses but i never get any of them...i'd say sell that 12:1 FMU and buy a 7:1 FMU...even 8:1 will do fine...FMU's are great for temporary and its a good cheap set up however they are risky and you need to keep it safe...12:1 is not safe

[Checkered-Member]

FMU’s are good to low boost levels some will tell you 6-7

I personally wont run more then 5

[Craving4Boost]

sunny..while we talking about how much boost you can do with a FMU...i want to warn you that there has been a problem with the WASTEGATE from BD...i thnk someone said it has a 14.7psi spring...just letting you know

[hysteria]

search the forum before asking things like this. i and many others have explained this plenty of times... i even remember posting this exact information less than a week ago.

checkered member is incorrect.

it does not matter whether you have a 12:1, 8:1 or 100000:1 fmu, your maximum fuel pressure is completely dependent on the ability of your fuel pump to make that pressure. so if you're like pretty much everyone with an fmu setup and you have a walbro 255 lph pump, the fuel pressure cannot just rise without bound as boost increases. it will stop rising as soon as the fuel pump maxes out. the reason why 8 psi is generally the maximum safe boost pressure is because at that point the fuel pump is maxed out and simply will not flow more fuel to compensate for extra air for like 10 psi...

what all of this means is that whether i have an 8:1 or a 12:1 rrfpr at my peak air flow the air fuel ratio will be ~the same because the max pressure of the fuel pump will have been reached... if you increase boost beyond this point you will just start leaning out, no matter what rrfpr you have. i'm not sure what exact max pressure for a walbro pump is, but on an 8 psi setup both an 8:1 and a 12:1 fmu will max out the fuel pump. the only difference is that the 12:1 will do it sooner... at lower boost, which means that you will be running consistently richer on a 12:1 fmu...i think the reason people would use a 12:1 fmu is that the extra fuel (richer condition) will provide a little more safety from detonation, but at these low boost levels using a 8:1 rrfpr is just fine.

oh and i (and many others) have a 12:1 fmu on an 8 psi setup and there have been 0 signs of anything "blowing."

i'm gonna go find that post i made maybe a week ago... i swear it will sound identical to this.

hey look at that... i didn't even have to go beyond the FIRST PAGE!!!!!

zer...age=1

there's the link...pretty much identical information.

[scheffler]

i agree but if you are worried about bursting something you can get a recalibration kif for your fmu and make it 4:1, 6:1 whatever you want to use and the waste gate with BD kit is a 1 bar spring i had to change mine when i got it

[hysteria]

yeah, you can always get other discs and recalibrate an fmu.

[Checkered-Member]

oh and i (and many others) have a 12:1 fmu on an 8 psi setup and there have been 0 signs of anything "blowing."

Do you have a fuel pressure gauge? Whats the max psi you are getting?

I was visiting my friend in Washington last summer, to help him turbo his 1996 altima.

Walbro fuel pump, stock injectors and a 8:1 fmu, we had trouble running the car because the FMU kept drowning the combustion chamber with fuel, and when we did get it up to speed at 7 psi we got 100+ psi of fuel pressure (I say + because the fuel pressure only went to 100 auto-meter full sweep fuel pressure gauge) , injector 3 and 4 were stuck open and injector 2 didn’t open which caused the #2 cylinder to detonate (minor injuries with only blown piston rings)

So you are telling me you are running 140+ psi with no problems?

I bet you have a restriction in your fuel system that won’t allow the pressure to be any higher then 90

[hysteria]

what i am saying is that the MOST common, by far, fuel setup for a turbo car is an fmu because it is the cheapest.... there are tons more people just running little fmu setups then there are any other setup, by a long shot. the majority of people have no problems. i am part of that majority. is an fmu setup the safest? hell no. is it better in any way than any other costly setup? not at all. does it work for low budget, low boost applications? yes.i never said my fuel pressure was 90 psi. i was just saying that the reason people generally don't go above 8 psi on an fmu setup is because of the inaccuracy and the capacity of the fuel pump... walbro pumps have their limits... they aren't exactly high dollar pumps.if i had some restriction or something in my fuel line my car would have leaned out and my engine would be dead by now. i've had this setup for ~half a year now.