Fmu!!!!

[Happy]

My roomate is selling is fmu of his supercharged trans am !!! And i was wondering if this is any advantage to me with stock injectors and stock fuel pump??? The Fmu is some sort of fuel management for turbos and superchargers! It works by t ing in on your fuel line and it is 12 point adjustable!! it works of vacume as well iguess for every pound of boost it pinches of the return line !! Not a 100% sure how it works yet but he asked me if i be interested in it !! But i dont want a buy it if its no advantage to me!! Thanks guys for your info!!

 

[kpt4321]

No, you don't want it.

The FMU is a rising rate fuel pressure regulator. They come in different ratios, such as 6:1, 8:10, 10:1, 12:1, etc.

Let's take the 8:1, for example. That works simply by raising fuel pressure 8 psi for every 1 psi of manifold (boost) pressure. SO, it you have 45 psi of fuel pressure base (with atmospheric pressure in the manifold) then you will have 53 psi of fuel pressure at 1 psi of boost. Now, one of these goes into offsetting the pressure in the manifold, so you really just get 7 psi more fuel pressure per pound of boost.

This works out to about 55% more fuel at 10 pounds of boost in the manifold. The fuel pressure would be like 115 psi, which is NOT a good thing.

This would throw your fuel curves way off, because the ECU depends on a linear increase in fuel pressure with regards to boost pressure.


....Kyle T.
93 TSi AWD "TURBO4"
14b - 12.8 @ 108

 

[DSMJim]

You are absolutly correct with regards to a car that comes turbo from the factory, however cars that come NA have no way of controlling fuel an FMU is just the ticket. Your car is an RS turbo. Did you put a turbo on a non turbo motor or did you swap in a 4G63 motor and computer etc etc from a turbo car that is already setup for adding more fuel pressure with boost??

10:1 works just fine because as boost builds on most cars it goes right upto say 10psi in a few seconds so your air fuel stays in tact.

Also you will never acctually see 115psi of fuel pressure as most pumps will never make that kind of pressure, If your running a 10:1 with 10psi in theory thats adding 100psi of fuel, but that will obviously not happen, it will bump your fuel to about 85psi at wot with 10psi of boost. If you tune with an AFC and some larger injectors it will keep a proper air fuel ratio right through the band. Even without it's pretty damn close.

Corky Bell invented the BEGI or Cartech FMU which is what we like to use for non turbo cars (Hondas primarily). It's 10:1 and works like a charm. It's also adjustable to set base fuel pressure unlike a vortec unit. If your motor is a turbo motor from a turbo car then an FMU is totally useless for you.

 

[DV8tion]

When I first put a T-3 on my 91 AWD I tried to use the FMU from my mustang to correct the fuel mixture. It would run out of fuel at like 12psi. This was before I got the VPC/GCC/660s. I used a bleader system to try and adjust it, it worked OK but always ended up too rich and I never realy trusted it It was a cool experiment, but not practical.