The be all to end all "Fake Skylines" thread
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By joshuaho96 · Posted
I thought the problem with doing this is the engine needs more timing and therefore is actually less efficient? Modern engines need very little timing to get to MBT, those super sharp edges on the squish pads are probably not the right way to get there but doing away with it entirely doesn't sound right either. -
this explains the possibility of several maps with different boost levels -
ok, I understand much better how we can control the boost and increase the number of psi before opening the wastegate
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Well.... yes and perhaps no. It depends on what you mean by "spool". For most of us, the point that we would describe as where the turbo is "spooling" is the point where the wheel speed gets high enough for it to start making some boost. This is coincidentally around about the point where it starts making noise - hence the "spooling" sound. If that is what you mean, then no - the wastegate should still be shut at this point. The boost will still be way below the point where it should start opening. If, on the other hand, you mean "spool" as "reach full boost", then yes. At the point where the boost has reached target, then boost control has already started. The wastegate is already open, and has been for some time. Some short time, definitely, but still, some time. If you have no boost controller - just the wastegate actuator connected to the boost source, then you have a mechanical system working as a pressure balance. There is pressure on one side of the wastegate actuator's diaphragm from the spring, and pressure on the other side coming from the boost measurement location (the "source"). This is not a digital thing. The wastegate does not stay shut until the boost pressure reaches the spring "pressure". The spring will start to compress as soon as you start to apply any pressure onto it. This can be controlled somewhat by adding pre-load into the spring, but you cannot add enough preload to make it into a digital switch behaviour. The wastegate will crack open and start to leak exhaust out (and therefore not though the turbine) well before you reach the target boost pressure. Electronic (and some mechanical/pneumatic) boost controllers will act to prevent the boost source applying pressure to the actuator until just before you reach target boost, thus preventing the wastegate from creeping open. And some boost controllers will apply boost pressure on the spring side to further push it shut. And this can be be necessary because the exhaust pressure in the manifold also pushes on the wastegate valve and tries to open it and you cab get it leaking even without it being connected to the boost source. -
By Dose Pipe Sutututu · Posted
A stand alone boost controller will not give you the control you need, unlike a modern ECU. Your boost will always naturally target the wastegate's opening pressure first, your controller then will allow you to add more boost as required.
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