Yeah, that's why I was confused about the mechanical creep. The WGDC values I've seen in the maps I've looked at don't seem to allow for adjustment to end up anywhere close to zero. Ming: what you're talking about could probably be accomplished by drilling a hole in the WG arm and repositioning where the actuator arm connects. Not sure what it'd do to the actuator spring (other than effectively weakening its effect), but that could be changed out. Of course, unless that approach offers additional advantages, it's no less of a pain than a quick dremel job. And while we have SS on the line, if he doesn't mind... all the WRX WGDC tables I've seen start off way high (90-ish %) and then go down to 60-65 at high throttle/rpm. The STi ones start off at 0 and go up to 60 or so. Why is that?
two ways to achieve it Use a mid pivot point and place the actuator and wg on different radius or move point of connection closer to the WG pivot point (minimum effect but still a little)
Well, not TOO small of an effect. If the WG arm is ~.75" or so, and you move the connection .25" closer... say it's opening 20 degrees now. Tan 20 * .75 = ~.273" that the actuator arm moves. If you get the connection down to .5" you'd be looking at something like 28-29 degrees which is a significant improvement.
Just for the record i had massive creep on my legacy in the cold of ohio (neg 10?) so it can happen to the non STi turboed 2.5 too. I hit 22 psi and only noticed it on the boost gauge when the fuel cut, cell came on , etc. Scott did say my turbo loved to make boost...
Thank you Scott, the angle of the WG is what I failed to mention in my original post and helps tie together my original writings. I wanted to just throw this out there for those of us who arent necessarily 100% certain on how wastegates actually work. More to come (when Im not in class).
I'll go ahead and add this... (SS correct me if I screw up!) On the compressor outlet there's a nipple that connects to a hose. This hose connects to a plastic 'T' which goes to the actuator and to the boost solenoid. If the boost solenoid keeps its line blocked, then all the boost pressure from the compressor side will go into the actuator, fighting the actuator spring pressure, and pushing the wastegate open (around 7 psi on a WRX). If the boost solenoid bleeds off air the actuator sees less pressure and will not open the wastegate or not open it as much. This is how boost is controlled. The wastegate duty cycle is a % of time that the boost solenoid bleeds pressure off. 100% WGDC means it hangs wide open and boost will build as high as it can (probably limited by how stiff the actuator spring is as well as the turbo exhaust side design itself), as the actuator isn't getting any feedback/pressure from the boost line. 0% WGDC means it's closed off completely and all the boost from the compressor side will act to push the wastegate open. The latter is how Cobb has their 'economy' maps setup; you just get whatever boost you'd see if the boost solenoid wasn't there and the actuator and compressor side were directly connected.