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I was actually going to try and dig out a datalog with turbine speed and EMAP haha -
Wait until @Lithium posts a compressor map and tries to explain what's going on. There is a strong possibility that the OP lives in a digital world and is not comfortable with analogue machines. A turbo is just about as analogue as it gets, with plenty of non-linear behaviours added in on top. Most of us who think we know how they work are actually only getting by on 2nd and 3rd order mental models that abstract away from the actual physics and bring it back to the sort of kindergarten level concepts we can hold in our heads. This is important when you need to hold 10 such concepts in your head at the same time. You need to reduce the complexity of the individual concepts to allow them to be simultaneously held and manipulated. Too much complexity in the base models makes it very difficult to make them work with each other mentally. -
It could be. It might not be. It is impossible to know without context by asking the owner or the tuner on the day and knowing what they were doing/not doing/attempting to do. You said earlier this is hard to understand because to your mind, a turbo is at full speed when it hits its spike. This is not true. The turbos actual speed is defined by how much air is being forced through it via the exhaust, unless you control it. The spike you are seeing at ~whatever RPM it 'spools' at, is where boost control is starting. If there were no boost control the turbo absolutely would be spinning much faster at 7000rpm than 3000rpm, every single time, on every single engine. Boost control keeps the boost controlled within the limits you ideally want. If it were uncontrolled you would have two scenarios 1) You have a turbo that hits peak RPM and CFM (not boost) at the redline of the engine. This would work, but most people want more boost earlier. 2) You have a turbo that hits peak RPM well before the redline of the engine (say, 3500), and you explode the turbo by redlining the engine. (say, 7000rpm). If you don't want exploding things, or lag, you design a turbo system to come on when you want the boost to be useful, and then not overspin itself into oblivion by using some form of boost control, to control the boost pressure accordingly. -
Yep. >10 posts required. Prank can relax that for individuals when required.
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@PranK is there a restriction on posting pics based on post count?
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