newbie sounding boost leak test question

[MyBeatGSX]

I was looking at how to make boost leak testers and reading topics on people doing it, but one thing isn't clear to me. You attach the tester to the turbo inlet, then you pressurize it. Ok so why doesn't all the air just blow through the ISC passages, go into the engine through open valves, and blow right out the exhaust? I don't see how you can get anything to hold pressure like that.

And how are people using there normal boost gauges to read any pressure on this test? Same as before, those are in the intake manifold. How could that see or hold any pressure with open valves?

 

[DSMvroom]

supposedly at TDC or like 10 degrees after TDC, the valves are all closed.

I personally wasn't able to successfully complete a boost leak test; the system would not pressurize. I did more homework and found people advise to set the crank at TDC or iirc, 10 degrees past TDC.

 

[MyBeatGSX]

This gets more and more involved. I'd have to draw a picture or something, but I didn't think there's ever a point when ALL the intake valves are closed....

I'm ready to just replace everything between the turbo and the head. It will be a lot less hassle.

 

[No_Skillz]

If intake valves are open, exhaust valves will usually be closed, and vice versa. Some combustion chambers will be holding pressure. That's one of the reasons you shouldn't pressurize more than 20 psi or whatever boost you run, since you can damage the internals.