Originally Posted by ballin
the reason you dont hear it on a ERST is because the metering unit muffles the sound.
The metering unit doesn't muffle the sound as such - it actually stops air exiting back thru it and out the air filter.
If you go and take the air filter or air box off your RST, you will see a big round metal "plate". Push this plate with your finger and it will go down. this is what happens when air is sucked in via the air filter/box. Basically there is an arm attached to this plate, and it pivots. As it pivots fuel is metered equal to the amount of air entering the engine (judged by how far the plate has opened)
Now, this plate can open donwards, and it closes upwards. But it can only go so far up then it stops. When it stops it i fully closed.... You lot following me?
Like a throttle butterfly - when you lift off the throttle to chage gear, slow down etc, the throttle butterfly snaps shut preventing air from entering the plenum. Likewise the plate in the metering unit closes preventing more air from entering the turbo/charge air system, etc.... With a normal dump valve in place, the air trapped between the throttle butterfly and the metering unit plate can escape thru said dump valve.
But with no dumpvalve, the charge air cannot escape. Still follow me?
It can't go in the plenum as the butterfly is shut and it can't exit via the air filter as the metering plate is shut..... or at least it should be
Bet your lost now
"Chatter" is the term given to the noise you hear when charge air is "chopped" by the tubine blades as it passes back through the turbochager and out the air filter.
BUT! On an MFi ERST the charge air should not be able to escape through the air filter as the metering flap should now be shut, preventing air from escaping....
So how does your RST get chatter? Logic points to the fact that your metering units are not doing the job they should be doing, and allowing air to escape when they shouldn't be...
The only other explanation is that air is escaping from between the turbo and the metering unit, of which there should only be one section of pipe/tubeing.
Get both your metering units and this piping checked out, as if either are leaking air then your fueling is not going to be right - ie: if your metering unit is allowing air to escape back thru it, then how can it be functioning properly, therefore how do you know it is metering the fuel in ratio to the air flow? Or, if the pipe between turbo and metering unit is allowing air to escape, then how do you know it isn't bleeding it off under boost/throttle, therefore the already metered fuel/air ratio is screwed up again as there is now more fuel than air since some has been bled off......
Worth checking lads, deffo worht checking - all in all could well lead to under or over fuelling both of which usually result in destroyed pistons/heads/rods