Explain FMUs To Me Please
 

I know about the ratios. What I need to know is if the 4:1= 4psi of fuel pressure per psi of boost + any of the stactic FP? I need to figure out what disk to use.

This is the combo now - 76mm MAS,70mm TB, KB blower(9#s), 24# inj.,stock lower IH&C,1 5/8 headers,O/R X-Pipe, Borlas turned down. I have a 8:1 in there now but, I don't think with the stock lower end it needs that much fuel. Maybe I'm wrong, school me. At 80 psi the 24s are at 38.1 lbs/hr.

Yes. a 4:1 FMU will add 4 psi of fuel pressure for every psi of boost on top of the static (zero vacuum zero boost) setting of your fuel pressure regulator. So if your "vac line off" fuel pressure is 38 psi, and you see 10 psi of boost, fuel pressure will spike to 78 psi.

Thanks, I was hoping it was only half the static FP. Old girl is really rich then.:p

I thought FMU's were just boost sensitive regulators operating at a different ratio than the stock 1:1? So a 4:1 FMU running 12 psi would produce 48 psi of fuel pressure (total). 6:1 would produce 72 psi (total).

Otherwise, think about a stock setup.
10:1 FMU, 8 pounds of boost, would mean 80 psi on TOP of your stock settings? That sounds really off to me.

jonnyk
 

I think you're right(but I could be wrong:D ). Thursday night at the track, 12 psi with an 8:1 disk, resulted in a 1st to 2nd shift backfire.

interesting, Vortech sent us the recalibration kit for the 24lbers and she backfires a little when revv'ing and when coming off throttle........

I dropped it down to a 4:1 to see if that cures it. I also have a 255 lph intank hi pressure fuel pump. That might be putting more fuel in the lines than needed.

Just make sure you put the FMU on right.........

PWR_RYD93 is right, 4psi for every # of boost.

Before winter hit, I had not had a chance to get mine set correctly. I was seeing upwards of 85PSI at WOT and 8#s. WAY to much. I got a BEGI and it does not use a disk, there is a bleader valve that controls the ratio. I am trying to get it around 60psi at WOT

Thanks!