FMU QUEStIONS>>HELP!
12-29-2002, 02:03 PM
#1
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Thread Starter
Join Date: Dec 2002
Posts: 32
FMU QUEStIONS>>HELP!
hi...
what is a fmu?
is it the cheapest way for fuel management if i wanna boost my civic dx engine?
what are the advantages of using the FMU over the others?
what FMU ratio should i buy?
thanks in advance
what is a fmu?
is it the cheapest way for fuel management if i wanna boost my civic dx engine?
what are the advantages of using the FMU over the others?
what FMU ratio should i buy?
thanks in advance
12-29-2002, 02:46 PM
#2
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Join Date: Dec 2002
Posts: 463
Re:FMU QUEStIONS>>HELP!
An FMU is a self-regulating unit which reacts under a signal from the intake manifold. To make it sounds simple, it regulates fuel when boost is sensed in the intake manifold (pressure produced by the turbo).
FMU stands for Fuel Management Unit. Is it the cheapest way to use? Well, it depends on how you look at it. If you are just gonna boost low and can not afford a stand alone system, then YES. It's a must to have a fuel enrichment unit to go with forced induction.
Get a vortech 12:1 FMU but that also depends on your boost level. I would sell you mine but I'm still working on my VAFC hack.
FMU stands for Fuel Management Unit. Is it the cheapest way to use? Well, it depends on how you look at it. If you are just gonna boost low and can not afford a stand alone system, then YES. It's a must to have a fuel enrichment unit to go with forced induction.
Get a vortech 12:1 FMU but that also depends on your boost level. I would sell you mine but I'm still working on my VAFC hack.
12-29-2002, 06:16 PM
#3
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Posts: n/a
Re:FMU QUEStIONS>>HELP!
Another name for a fmu is "raising rate fuel regulator"
that is to say it rises the fuel pressure, as air pressure increases in the manifold... lets say your current fuel pressure is 20 psi max, now you add 25 psi of boost,, The pressure in your manifold is 5 psi higher than that of the fuel rail.. "what direction do you supose the fuel will go when the injector opens?" Invisioning this you can see the "NEED" for an fmu on boosted app's. this really just touches the surface of the topic. there are alot of other points to consider as well.
that is to say it rises the fuel pressure, as air pressure increases in the manifold... lets say your current fuel pressure is 20 psi max, now you add 25 psi of boost,, The pressure in your manifold is 5 psi higher than that of the fuel rail.. "what direction do you supose the fuel will go when the injector opens?" Invisioning this you can see the "NEED" for an fmu on boosted app's. this really just touches the surface of the topic. there are alot of other points to consider as well.
12-29-2002, 06:44 PM
#4
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Join Date: Dec 2002
Posts: 38
Re:FMU QUEStIONS>>HELP!
Originally Posted by thermalfi'd16
Get a vortech 12:1 FMU but that also depends on your boost level. I would sell you mine but I'm still working on my VAFC hack.
12-29-2002, 07:11 PM
#5
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Join Date: Dec 2002
Posts: 10
Re:FMU QUEStIONS>>HELP!
wildman- you were a little unclear on your post- figured I might clarify a bit.
I'll use real numbers for everyone
Ok:
Stock fuel pressure is 42 psi
Max Boost is 5 psi
FMU has a 10:1 disc in it (10psi of fuel pressure rise per 1psi of boost)
At full boost you have 92 psi of pressure.
Final pressure = Stock + (Boost * Disc)
FP = 42 + (5 * 10)
FP = 92 psi
As for which disc to use- which DX do you have? I have a 1988 4dr DX with B15B2 dual port engine. Until 19:00 tonight I was running a Garrett T3 @ 5psi with a 4:1 disc on my FMU and a Holley 190 LPH fuel pump. That was all well and good until it went under boost, then the fuel injector would snap shut because it wasn't designed to flow as much fuel as my engine was trying to consume. Supposably if you have a MPFI engine (1991 CRX Si or any 1992+ engine) you won't encounter this problem, and the most common disc used is the 12:1. Your best bet is to find an FMU (mine was $75.00 on ebay) and buy a full recalibration kit(~35.00 at Vortech). This will allow you full versatility on cheap fuel management. Check cheapturbo.com first to see if they carry any of these parts. At any rate remember to use either a high pressure in-tank pump or a high pressure inline pump mounted close to the fuel rail. My setup used the factory in-tank unit as a primer pump for the inline, then the inline acted as the pressure riser pump.
I'll use real numbers for everyone
Ok:
Stock fuel pressure is 42 psi
Max Boost is 5 psi
FMU has a 10:1 disc in it (10psi of fuel pressure rise per 1psi of boost)
At full boost you have 92 psi of pressure.
Final pressure = Stock + (Boost * Disc)
FP = 42 + (5 * 10)
FP = 92 psi
As for which disc to use- which DX do you have? I have a 1988 4dr DX with B15B2 dual port engine. Until 19:00 tonight I was running a Garrett T3 @ 5psi with a 4:1 disc on my FMU and a Holley 190 LPH fuel pump. That was all well and good until it went under boost, then the fuel injector would snap shut because it wasn't designed to flow as much fuel as my engine was trying to consume. Supposably if you have a MPFI engine (1991 CRX Si or any 1992+ engine) you won't encounter this problem, and the most common disc used is the 12:1. Your best bet is to find an FMU (mine was $75.00 on ebay) and buy a full recalibration kit(~35.00 at Vortech). This will allow you full versatility on cheap fuel management. Check cheapturbo.com first to see if they carry any of these parts. At any rate remember to use either a high pressure in-tank pump or a high pressure inline pump mounted close to the fuel rail. My setup used the factory in-tank unit as a primer pump for the inline, then the inline acted as the pressure riser pump.
12-29-2002, 07:39 PM
#7
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Join Date: Dec 2002
Posts: 10
Re:FMU QUEStIONS>>HELP!
theoretically the higher the ratio (12:1 as compared to 3:1) means you can run more boost. However, your car might only need a 6:1 disc to stay in the stiociometric range (not too rich, not too lean). The fuel pressure goes up as the boost goes up, so you get more fuel as you make more boost. Your best bet is this:
Install turbo kit with 12:1 FMU
Set your timing at 9 degress BTDC
go to dyno, do a dyno pull with their O2 meter hooked up
If you're running too rich, go down to a lower ratio disc (10:1, 8:1, etc)
If you're running too lean.... well, you can't run too lean with a 12:1
B*
Install turbo kit with 12:1 FMU
Set your timing at 9 degress BTDC
go to dyno, do a dyno pull with their O2 meter hooked up
If you're running too rich, go down to a lower ratio disc (10:1, 8:1, etc)
If you're running too lean.... well, you can't run too lean with a 12:1
B*
Thanks...I just gotta find a shop that will tune my car. 
12-29-2002, 08:29 PM
#9
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Join Date: Dec 2002
Posts: 10
Re:FMU QUEStIONS>>HELP!
what exactly do you mean by "tune?"
Setting the timing is as easy as loosening 3 bolts, moving the distributor while pointing a timing light at your timing marks, and retightening them.
Changing the disc on the FMU requires removing six (6) socket head cap screws, putting in a different disc, and putting the screws back.
Hit me up on AOLIM- Yeah Low
B*
Setting the timing is as easy as loosening 3 bolts, moving the distributor while pointing a timing light at your timing marks, and retightening them.
Changing the disc on the FMU requires removing six (6) socket head cap screws, putting in a different disc, and putting the screws back.
Hit me up on AOLIM- Yeah Low
B*
