Garrett Gt3540/highmount Manifold/ex-wastegate/screemer/tomei Head Gaskit.
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As someone who has been playing with turbo things for some time now, be prepared for this to not be the first time feeling this way I'm busy as atm, but if no one else covers the things I'm realising are worth mentioning to you then I will when I have a chance as it seems like I overestimated your knowledge on how turbos and wastegates work. Otherwise I recommend having a look around how wastegates and boost control work, really anything on understanding the general mechanism of boost control as it will help you find the answers to the questions you're looking for. Your initial question jumps some fundamentals. -
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so this is an anomaly??? I thought it was a voluntary increase
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we can only guess exactly what happened from our keyboards, but to me it looks like they were targeting 27 but the wastegate was too small or poorly controlled and the boost crept up, that is quite common -
Good points! Took those for granted - though I *did* actually give an example of winding boost up more than it had been before where I wasn't actually specifically looking for more peak power. The Toyota Starlet dyno plot that I shared and mentioned showed an overlay from the previous tune it had and the one I'd redone, I left the boost targetting the same as the old tune but then after peak power I ramped boost up by a good 5psi or so over what the old tune had at the same rpm. The reason I felt comfortable with this (though the owner of the car had a "are you sure?" moment when I suggested it) is that the setup wasn't turbo limited, it was largely head sealing limited and the owner was a bit concerned as for the last few seasons he'd had issues with head lifting - sometimes not completing an event without having some headgasket issue, so he didn't want to run any more boost than it was. The reasons I was ok with raising the boost a good 5+psi MORE than that was that I left it where it was in the middle, and only increased it where VE (and therefore cylinder pressure vs psi) were dropping hard and I didn't stop the torque from dropping, just reduced the drop. Well, there is that and the fact that the previous tuner had it overtimed by near 7degrees at peak torque - but that's another story haha. I didn't really go into detail about that "turning it up more" thing but now you've mentioned the "not detuning", sometimes the boost *can* be turned up higher than you'd expect if the setup allows for it and you do it smartly. I've tuned things to run 30psi on BP98 "safely" that a few years ago (or still?) people would cry that it was a stupid idea - but given they were well intercooled, low EMAP turbos and only doing that kind of boost where VE is dropping etc I was pretty confident it wasn't as cowboy as it sounded at face value and we never ended up with issues as a result of it.
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