Why the 100# limit?

[megawatt]

I have read many times people say a FMU system bike should keep the fuel presssure below 100# when on fulll boost.  But I have never heard the reason why?

I have noticed when I run 8# of boost the pressure is about 80# but when I activate the 2nd stage boost controller on 13# my gauge does read 110#.  I have S2000 injectors and RCC stage 1 turbo on a fully built motor.  Problem or no problem would you say?

[kawaking]

The Injector will lock or stay shut at those pressures as the solenoid wont have enough power to pull it up !
Just consider your self lucky !

I would not keep trying it !

they should change the name from stage 1 to 1 stage turbo system !

[OzBooster]

the other aspect is fuel pump flow, as pressure rises flow drops off, at 100 or so the flow may be less than demand

[megawatt]

I know once you start changing FMU settings its time for retune.  But I am guessing the way to correct this high pressure when under heavy boost is to unscrew the bleed valve on the FMU so it does not hold that high of pressure?

[OzBooster]

Double edged sword there , you need the pressure or the injectors can't flow enough
RCC Richard has commented often that the adjustment only changes the onset rate and not total pressure , but i think if you had a restrictor so the needle valve on the outlet could flow a large % of the air going through the restrictor you could adjust the internal pressure in the air chamber of the fmu up or down as required , just like some bleed valve boost controllers do to the internal wastegate

but doing this must upset the fueling at the onset of boost or no doubt Richard would be recommending it   

[kawaking]

dont touch the set screw ! you will mess up the tune and blow your motor !
just run low boost ! you want to run more boost ! upgrade to secondaries !!!

[megawatt]

Well I am finding out there is no traction on these city streets here in the Summer.   Was not really an issue before when I only had 6# on stock engine, now I am not finding too many times that I want to hit over 10# of boost.  It just takes way too much real estate to stop.  Today it was 113F.

Bike has water injection and was mapped from 7 to 13 lbs of boost with boost referencing.  I will keep the fuel pressure so it stays below triple digits by limiting the boost to about 11#, not touch the FMU and just ride. 

Thanks for the info guys.

[kawaking]

thats the best thing you can do !!!