I HAVE STARTED RALLYING IN A MY99 IMPREZA GROUP N4 IN SOUTH AFRICA.THE FIA RULES STIPULATE THAT A 32mm RESTICTOR BE USED ON THE TURBO. A VF24 TURBO IS BEING USED.MY PROBLEM IS THAT WHEN BOOST RISES IT GETS UP TO 1.1 BAR BUT AT 4200RPM IT STARTS DROPPING ALL THE WAY TO 0.6 BAR WHEN 6000 RPM HAS BEEN REACHED.FIA HOMOLAGATION STIPULATES NO AFTERMARKET BOOST CONTROLLERS ARE ALLOWED.IS THE BOOST DROP FROM THE BOOST CONTROLLER OR MAYBE THE RESTRICTOR THATS CAUSING THE PROBLEM?

 

Its the restrictor that causes this. There is only so much air can get through a 32mm hole and basiclly the engine can't get all the air it wants so hence revs are reduced.

 

if you run to FIA regs then you CAN change the ECU and doing this (with something like a GEMS or MOTEC) will help maintain boost across a wider rev band, however because of the restrictor you will find that the car does not rev as well as std (ours has usable power between 2000rpm and just over 6000rpm)
this makes the onus on TORQUE as opposed to outright power!!
you need to "short-shift" to keep the car in the boost and help make the most of the power!!

alyn - as performance