questions about wastegates.
 

a wastegate is open at full boost right? thereby letting the exhaust out via a route that does not go through the turbine. (am I correct so far?)

If a wastegate were set at 8psi, it would gradually open (in the case of an internal wastegate) until 8psi and then it's be fully open right?

then what? what is the wasteagte doing at full boost? does it stay all the way open? wouldn't that make you lose boost by not having enough exhaust go through the turbine?

what prevents the boost from changing when the wastegate is fully open? i mean whether i have the wategate set at 1psi or 123psi it would still be open under full boost conditions, what makes the difference between the 1psi and the 123psi?

Re:questions about wastegates.
 

boost creep could occur bcs your wastegate is to small.

but even a 30mm WG on a log manifold never gets to that state unless its like 4 feet from the manifold :)

thats why DSM turbos get creep bcs of the shitty placement and the small hole..

everything else your dead on.

Re:questions about wastegates.
 

ok, but what happens at full boost? when the WG is all the way open? what makes a all the way open wg at 4psi different then a WG in the same position at 17psi? how does the turbo "know how much boost to make? also, how is that boost pressure physically sustained when the conditions of the exhaust change but the WG stays open?

say you make full boost (we'll say 8psi) at 3500 rpm, the exhuast conditions can't possibly stay the same from 3500 to redline, but the wg does? then what regulates how much boost you make?


I'm just not understanding how with X exhaust conditions and Y amount the wg is open (as a constant in our case cause it's all the way open at full boost) how could X*Y=5psi and X*Y also = 17psi?

Re:questions about wastegates.
 

you're asking kind of a weird question there. the wastegate works by using a feed line to oppose a diaphragm that is acted upon on the other side by a spring. The spring is displaced by an amount equal to the force on the diaphragm divided by the spring constant (x=F/k). This force, F, is the pressure (6psi) times the normal area that the pressure acts upon (pi r^2). The spring is chosen so that at a certain pressure (like say 6 psi), the force from the diaphragm is enough to displace the spring thereby opening the wastegate valve. The reason why boost level becomes stable is because a wastegate is basically a continuous feedback system. For example, if the wastegate loses more exhaust energy than intended, boost pressure will drop, but so will the pressure in the wastegate feed line, which closes the valve a little to compensate. This continuous feed back allows the wastegate to hold the pressure stable. The only limitation is if the wastegate vent hole is so small that choking occurs and the exhaust gas is forced to go somewhere else - the turbo. This is how boost creep happens. I hope I answered your question.

Re:questions about wastegates.
 

in other words...the wastegate is only fully open if the boost is set at something close to nothing

Re:questions about wastegates.
 

that makes way more sense, that's exactly what I was asking.