If I'm in vacuum (like at idle)... does the fmu scale the fuel pressure down? Or does it flow the same as if it were see no boost?

Any insight would be great...

 

If its in vacuum, your FMU does not do anything except let the fuel flow back into the tank. It only raises pressure when it sees boost.

 

you may see a slight increase in idle fuel pressure because the FMU creates a minor restriction in the fuel return circuit.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by b18b98 &raquo;</TD></TR><TR><TD CLASS="quote">If its in vacuum, your FMU does not do anything except let the fuel flow back into the tank. It only raises pressure when it sees boost.</TD></TR></TABLE>

Technically, FMUs only raise fuel pressure after the boost pressure X FMU ratio exceeds base fuel pressure. Example: 10:1 FMU and 40 psig base FP = 40 psi fuel pressure until 4 psi, and then the FMU ramps it up.

Vortech has/had a nice tech writeup on FMUs... they don't work too badly for small power setups in a small ratio/large injector combo, where fuel pressures don't get out of hand. You see some examples of this in the Domestic world... with Hondas, by the time you buy FMU, injectors, something to control them, you could already have a standalone.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by J. Davis &raquo;</TD></TR><TR><TD CLASS="quote">
... with Hondas, by the time you buy FMU, injectors, something to control them, you could already have a standalone.</TD></TR></TABLE>

The FMU's in Honda make use with stock injectors, that's the reason for using it. Your right though it is very useful in low boost applications and works well when used right.

 

No, I said it works adequately in low fuel pressure setups - slight difference.

 

great info guys.. thanks... i was concern with how the fuel system is being effected... especially when im having trouble getting boost (exhaust leak.. )... thanks again...