so, i know the greddy wastegate has a reputation of dropping boost in the upper RPM ranges. now, i thought i read somewhere that it could potentially be attributed to the location of that nipple on the compressor housing that is used as a signal line. idea being that it's not in an ideal place to be used as a signal line.

would plugging that nipple and taking a vac signal from somewhere else help the issue, potentially?

 

no, it has everything to do with the weak diaphragm.

moving it to the IM might help, but i doubt it will do anything. Your biggest allie in the battle for cheap fixes will be a helper spring. This will provide more preload on the wastegate so it doesn't get blasted open and over-powered. It should fight spikes and dropping boost at redline.

 

sounds good. i'll have to rig one of those up once i have better injectors and the clutch in the car. for now i think i'm happy enough to drive it aorund as-is for awhile before it goes away for the winter.

 

Is it possible to change out the diaphragm? How does the helper spring mount and what spring is best to use?

 

you can take apart the actuator and replace the internal spring with something stiffer if you don't want to install a helper spring. i have tried doing this before to a different actuator (actually, i installed a softer spring because i wanted less boost) and they are designed in very similar ways. it is a bit of a pain because once you get the canister apart you have to worry about sealing it back up.

a helper spring would be much easier. to install it, all you need to do is put the spring in such a location that it helps to hold the wastegate flapper shut.

 

I've been told that plugging the existing souce and adding a new source further towards the compressor outlet will absolutely help stabilize boost control. I was told this by the dyno operator at a Subie dealer, who is pretty damn familliar with Mitsu turbos.

You don't want to source from the IM because then your actuator sees both boost and vac, which will shorten it's life.