Parting Out Modified 180sx With Rb20
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Either the WG is reaching full opening, or it is not. The "it is not" case could only occur if there was not enough time available to swing the valve fully open during that boost event. I would consider that to be unlikely, as this is a commercial product that is in use elsewhere, so it really should work. But in your case, because there is definitely SOMETHING wrong, it should not be assumed that things like that are working as they should. You should put a video camera where it can see the actuator (if at all possible) during a run to see how far it is moving. -
I think you're mostly on the ball there. With the straight gate, I suspect the weight of the spring will determine how quickly the gate can close, when not run with active pressure drive on both sides of the diaphragm. Otherwise, with drive on both sides of the diaphragm, you could almost go without a spring at all, only needing one to make sure that the thing was actually closed while completely off boost and not having pressure available to drive it closed. Butterfly valves have mostly symmetric loading when there is flow going through them, meaning that the gas hitting the upstream part of the blade is balanced by the gas hitting the downstream part of the blade, which means you don't need actuator torque to overcome any non-symmetric flow induced loads. But the gas flow does impart a purely normal load against the shaft, which transfers into the bush/bearing at each end of the shaft and does increase the torque required to make the shaft turn. Only a little, but it is there. I have no feeling for the amount of force involved in a WG application, but it certainly could make an argument for a decent spring weight being required. But all of this is just peripheral to the actual problem here.
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The answer to this would be I followed the documentation from Turbosmart which said each spring pressure could achieve a maximum of 5x it's rated pressure so the included smallest spring being the 6psi had a range up to 30psi. I went with the 12 because I figured it'd likely hover around 15psi as a base pressure however I was obviously wrong. I have a log here that I'll dig out that is purely wastegate and no Mac valve controlling anything. If it can't hold anywhere near 12psi, does that mean the straight gate is virtually wide open during a run? Or am I thinking about this all wrong. I could Tee Piece into the cooler pipe pre intercooler where the wastegate gets its feed, and send that to the ecu and see how that reads, I just don't have a spare pressure sensor currently that's all. -
By Murray_Calavera · Posted
lol nice, I wouldn't worry about sanding back the filler to check for rust then. Yep very much a thing. Personally I don't do the panel beating, its very easy to have a panel beater sort that out for you. If they aren't doing any prep work the actual panel beating generally doesn't take long at all. Have you taken before pictures before you started this project? I'd be keen to see the before and afters when you're done. -
Some good discussion in here, for the most part I can't really add too much to it - thought I'd add some notes to the datalog screen shot that probably aren't news to anyone but a good prop... this is assuming 25psi-ish should be the boost ceiling given the first post refers to 23psi. To state the obvious, this issue seems super weird. Turbo speed seems pretty lethagic to build, like the turbo isn't getting as much drive as it needs - and it doesn't help that wgdc keeps rising AFTER boost target then completely shuts duty at a point, which in theory should have the straight gate dump heaps past the turbo and funnily enough causes the huge drop off. It seems like pretty blunt boost control tuning but I'd not call that the primary issue, so much as possibly not helping the situation. I'm curious, what does a pull look like with purely mechanical boost control? Like purely wastegate? There are things in this log and story that make it sound like there could be a significant restriction in the intercooler piping or something - but then it's also overshooting boost target which is NOT what you'd expect with a restriction. I can see where people are coming from with the non-linear wastegate bypass (not that any valves are linear for this kind of thing), but it still doesn't make sense that it can't hold <20psi on a 12psi spring. Have you, or can you try measuring pressure pre-intercooler? Be pretty interesting to see what's happening there vs in the intake manifold - sorry if I've repeated old ground, I've kinda skimmed over but I could have missed something. In terms of comments regarding the wg spring being closer to boost target, I haven't used a straight gate but part of the reason for having close to wg target is about fighting backpressure as well - I might be wrong, but I'd have thought that part of the point of using a butterfly valve like the straight gate does you actually don't have to resist pressure at all, on EITHER side of the gate. It shouldn't need too much leverage to start opening, the spring being more to do with where it triggers opening as opposed to resisting boost & EMAP, though smarter people can correct me if I'm wrong there.
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