CHRIS575

I had probs with dump valve piston inside had seized up , i stripped it down cleaned it up and put back together, its working great but not sure if got correct adjustment, there is a bolt and adjustment thread on top which controls spring pressure for piston . anyone know when car should be dumping or how to set this up to get best performance

maydew

iTrader: (9)

trial and error set it so it goes off about 4k-4half and see if u get any lumpy tickover/boost issue

CHRIS575

so when i rev to 4 4500 and release she should dump, what does the adjustment do or how does it efect the boost

maydew

iTrader: (9)

it just stiffens the spring up so when you are on positive boost if the spring is too soft it will push the piston open hence leak....so i am led to believe lol

CHRIS575

so if to soft wil lose boost it was stuck proper and i had problems with car colding back and over boosting could this have been problem since i have repaired she is running well , alot better performance , will have to play around with it thanks for help

Adam K

It's not the spring that hold the piston in place when on bosst, the boost does that!
There is a hose to the top of the BOV coming from the manifold, as long as throttle is open pressure is the same on both 'narrow hose' side and IC-side of the BOV, but when throttle closes pressure in mainfold sinks and 'narrow hose' side have no pressure to hold back the piston with, piston moves and exposes opening to return-hose/atm for the IC-air, which releasese the pressure there and so balances pressure on both sides again. The spring pushes the piston back and so protects from minor pressure-differences and creates an initial inertia. If you have the spring to hard, boost wil stay in IC and against turbo compressor uneccesarily much, but if it too soft you risk it opening too early. A balance, that much is true!

maydew

iTrader: (9)

in theory the above is correct and does work but why are most dump valves adjustable,and why do hks and pirran mount the piston sideways so the pressure from the intercooler holds the piston down from the bk so is never pushing againt it.mine is mounted sideways,


in view my car is the pic of the old baileys one which leaked so went for the pirran recirc one which is turned right up and below 5-6 k flutters bk through the turbo anythin over it opens the piston on the dump valve