FMU question?
Thread Starter
Instructor
Joined: Feb 2000
Posts: 246
Likes: 2
From: Philadelphia Pa.
FMU question?
Well I finally bought a Powerdyne head unit to install on my car, but of course, I have more questions now than ever. The car is a 1986 Z51 coupe with a 383c.i., superram, Accel DFI, open exhaust racecar used for hillclimbs. The A.I.R. pump and A/C have been removed and the engine uses 24 lb. injectors. My biggest question is what FMU do I use for this engine? I should mention it has 10.5 to 1 compression ratio and uses racing fuel. Thanks for the imput.
Joe
Joe
Melting Slicks
Joined: Mar 2001
Posts: 2,150
Likes: 304
From: Timra, Sweden
I would not use an FMU on an engine that is that far from stock ... Get a custom chip instread.
A 10:1 FMU increases fuel pressure 10 psi for every psi of boost.
If you start at 40 psi fuel pressure.
At just 4 psi boost your fuel pressure over the injector will be 80 psi.
At 8 psi boost your fuel pressure over the injector will be 120 psi, or 128 psi (fuel pressure + boost) on a fuel pressure meter.
A 10:1 FMU increases fuel pressure 10 psi for every psi of boost.
If you start at 40 psi fuel pressure.
At just 4 psi boost your fuel pressure over the injector will be 80 psi.
At 8 psi boost your fuel pressure over the injector will be 120 psi, or 128 psi (fuel pressure + boost) on a fuel pressure meter.
Advanced
Joined: Aug 2004
Posts: 95
Likes: 0
From: Kansas City MO
i would not even use the FMU. go with a kick butt fuel pump, high end fuel reg ( aeromotive ) that reads boost and adds more fuel. 
i'm running a 383 with a vortech t-trim ( hoping for 14 lbs of boost ), i run twin 255 pumps in the tank and aeromotive reg. it will get the job done... 
i'm running a 383 with a vortech t-trim ( hoping for 14 lbs of boost ), i run twin 255 pumps in the tank and aeromotive reg. it will get the job done...
Melting Slicks
Joined: Mar 2001
Posts: 2,150
Likes: 304
From: Timra, Sweden
ANY vacuum referenced 1:1 fuel pressure regulator, Even the stock one, will follow boost to keep the differential pressure over the injector constant.
You will see higher fuel pressure during boost, but the differential pressure over the injector is contant.
A progressive fuel pressure regulator (FMU) will raise the fuel pressure more than the boost pressure to add fuel.
Your aeromotive regulator does not add any fuel, unless it is a progressive regulator, and it is probably not.
You will see higher fuel pressure during boost, but the differential pressure over the injector is contant.
A progressive fuel pressure regulator (FMU) will raise the fuel pressure more than the boost pressure to add fuel.
Your aeromotive regulator does not add any fuel, unless it is a progressive regulator, and it is probably not.
