fmu

[PhyRe]

i am lookin into a fmu for a junk yard turbo set up(93 civic dx stock) because i dont have the money for much more. but the question is which one should i get. my stock comp ratio is 9.2:1(HS) but they only sell 8:1 and 10:1 should i lower my comp into the 8s or raise it and if i need to change it how?
thanx

 

[JDMPlaya]

The most popular to run is 12:1

 

[posol]

compression and fuel delivery are not really related at such low levels. I think you are confusing fuel psi with compression and boost psi. you will be more than fine with the motor running at 9.2:1. mot people run mid 9's:1 on their hondas.

an fmu works like this:
your base fuel system runs roughly 38-42 psi at the fuel rail.
as the fmu sees boost (instead of vacuum) it rasises said ail pressure at a rate of (8/10/12):1, or say 12 more psi of rail pressure for every psi of boost it sees.
at 5 psi on a 12:1 fmu, you have added 60 psi of rail pressure to your 40-ish base, for an end result of abotu 100 psi of rail pressure.

While great in design and perfect for low-power, low-boost, small-turbo applications, the FMU is VERY limited.

A key thing to rememebr is that PRESSURE is NOT VOLUME. at some point, regardless of the pressure in the rail, the stock injector simply can't handel the volume of flow that is needed for the combustion process.

Along the same lines, you have to be able to supply the rail with that much pressure in the first place. Thus, an inline fuel pump booster is required, and an in-tank 255lph (litres per hour) hp (high hpressure) is recommended.

fmu size depends on your turbo size more than anything.
a dinky t25 will be fine on a 10:1 fmu at any psi
a t3/t4, will not.

Vortech makes a good 12:1 FMU
http://www.optauto.com/webstore/product_in...item=8&back=yes

 

[PhyRe]

vortech was what i was looking at
so just get bigger injectors(440?) and and a bigger fuel pump(which?) and with the adjustable vortech unit what is my max i can get out of a t25?
thanks for the info

 

[posol]

nope.

you CANT run 440s with an fmu. you will flood to all hell.

The whole purpose of the fmu is to run your stock injectors, but by raising rail pressure with boost, you can feed the extra fuel in with the extra air.

the most you could get away with would be 310s.

if you want to run the 440's...
look into doing the vafc hack. do a search on it, its been covered 23123 times.

 

[[Freemantle]]

Think of it this way. You are shooting fuel into your engine with a supersoaker. By raising fuel pressure (pumping the gun more times), you can deliver more fuel through the same gun. Or you could change injector size (buy a bigger supersoaker) to deliver more fuel that way. If you are doing both, your car will be so rich it wont even start.

 

[reckedracing]

to further this discussion....

which is better... the intank or the inline

91 civic hatch, with boost
12:1 fmu

255 intank, or 255 inline???

thanks

 

[posol]

depends on the application.

inlines are just pressure boosters, and are still limited to the in-tanks flow capability

 

[reckedracing]

so can you get the same pressure with a 255 high pressure walbro intank?

 

[posol]

depends on the style of the inline, but yes. the hp will flow 100 rail pressure, and support the 255 gph instead of the stocker's 120-ish

 

[reckedracing]

so an intank with no other booster will be enough to support the pressure needed for an FMU?

thanks for your help pissed

 

[posol]

a 255 lph HP will