Hey there I have a 1991 Nissan skyline gts-4. The motor is pretty much stock hits has an hks blow off valve, manual boost controller and turbo and minfold off an rb25.... So I was driving the car the other day started laying into it and all of the sudden a small pop and no boost. Turbo spools with but only builds to 0... Car idles perfect but when you rev up you can hear the turbo spool and it sounds like a jet taking off.... The car does smoke now. I have checked all of the inter cooler piping and no leaks....wastegate is still in good condition and is not stuck open...I am starting to think something let go in the turbo but I would like some feedback before I rip the whole motor out and just start fresh. Please help!

really? ur gonna rip the whole engine out over what could be a boost leak?? I would smoke test the whole intake from the air filter to intake manifold. break the test into segments, in front of and behind the turbo. but more than likely u wont find anything in front of the turbo.
U may have over boosted as well and the Engine software has gone into a default map or a limp mode of sorts. It gets u home and doesn't make damage with boost. Scan the car for fault codes. Back fires, burst pipes, or welds, sensors cracked, or vacuum lines broken open or off. Recirc valves and actuator solenoids work off vacuum, (and sometimes pressure) and if there is a check valve popped off or broken open there will be no stored vacuum to deliver to the actuators when those solenoids are activated by the ECM. No sense yankin a motor for a small issue if that's what it is.

I bought the car as a project so I just bought the car the way it sits. The car was running roughly 8psi when I got it and all of the sudden pop and no boost plus black smoke.... Typical piping blowing off but it's not. I've tested all of the inter cooler piping and no leaks. There's no boost even hitting the system. Another thing that's got me is it's burning oil now, but no residue in any of the intake, compression tested at 130 across all six and runs smooth. The wastegate is remaing closed like it should as well...just frustrating and can't figure it out.. I'd rebuild it so its my own and I actually know what's been done. The car idles rather high but I was told the tps was replaced and as far as I can see it has. What does an rb20 run for vacuum normally?

But thank you for the advice! I'm gunna look more thoroughly at this

Turns out oil is pissing out of the head.... Thinking bad head gasket