1991tsi

iTrader: (2)

From my understanding, the fuel system on most stock turbocharged vehicles (for example my eagle talon, now deceased) raises fuel press 1:1 with boost. So why do FMUs come in ratios of 8:1, 12:1, etc? How does one select the proper ratio to begin tuning a custom turbo setup?

Nismo3112

iTrader: (12)

BUMP 123467

ilumo

I would liek to know this as well

Confused

iTrader: (4)

the ecu on a stock turbocharged car is programmed to deliever fuel at that fuel pressure. a multiplying fmu uses higher fuel pressure to run more fuel through the injectors on ecu programming that was not designed for boost (as in an aftermarket kit with no ecu flash).. if your a pioneer its trial and error, otherwise you have examples of what other people did.

ilumo

ok.... but what does the ratio mean? like the 8:1 disk? Does that mean that when you go up 1lb in boost, the Fuel pressure will go up 8 lbs? That sounds like it might be too much... even the 4:1's... so if you have 10lbs of boost, with the stock injectors yo uwill have your base pressure, 25 psi? + 10x 8 = 105 psi at max boost?
I have an AEM Adjustable FPR now.. im not totoally sure how that works... but I also have a FMU... how would I use those in conjunction? or i cant, and wont have to? TIA

Shadow

iTrader: (15)

It's not quite calculated like that, I forget the actual calculation. But you're on the right track. 8:1 does mean that for every psi of boost, the fuel pressure gets bumped 8 psi.

AEM FPR allows you to adjust base fuel pressure. FMU doesn't do anything until boost starts. Until manifold pressure goes positive, the FMU isn't doing anything. They can and are often used in conjuction. If you have 370's and no e manage, then you need the FPR. Otherwise, it's really not necessary.

Confused

iTrader: (4)

1/2 of static pressure + (boost x fmu mult)
oem static pressure on the max is 34 so @ 10psi =
17+80=97, very common for a boosted max on stock injectors.

the rest is like shadow said..

subs1000w

wouldnt you use WOT fuel pressure which is 43psi for this calculation instead of idle pressure

1991tsi

iTrader: (2)

So does anyone know of any standards that have been generated by the turbo guru's yet? As in "for this boost, use this FMU and it'll be tuned properly." I'd like to build a cheap system without the fancy electronics.

ilumo

so which one is it? using the static FP or the WOT FP? im confused now...

Confused

iTrader: (4)

not that i'm aware of even though it seems logical. seems to work when i've tested the formula but even if you do use 43 you will only be 4.5lbs off.. not a big difference when your in the 90+psi f/p range. it don't mean a thing if you aint runnin lean.. lol