It seems more RPM dependent than boost dependent.

Try a run where you just ease up to 5K RPM and the floor it. See how much boost you get initially and if it tapers off.

If it maxes at about 8 psig and basically behaves just like it did in the data posted above for any given RPM over 5000, I am thinking that your turbo is simply unable to keep up with the engines demand for airflow. The WG is closed, all exhaust is hitting the turbine, but the compressor simply cant push enough air to make more than 7 psig. I dont know why it cant, but thats my guess.

If you do the above test and get a peak up to say 21 psi really quickly then tapers back down again, then I suspect a leak somewhere, such as a BOV.

 

Good point. I will try this out tomorrow.
For the record I suspected the bov too and I changed it, but guess what.. the same situation.
If is the turbo that cannot build boost I will take psychodrugs. I've already blown 2 turbos...used. This one was new from atp.

 

2871R should have a restrictor.

 

What happened to the other two? How far apart were the failures?

 

https://www.miataturbo.net/diy-turbo-discussion-14/two-turbo-failures-3-months-41564/

 

I have some news. Very bad I am afraid.

I took out the turbo and pressurized air from the inlet and tapped the outlet.
Guess what. The air passed through oil exits. Both feed and return. When I tapped the oil in and out the air escaped around the compressor where the compressor housing bolts.

I destroyed another turbo.. again. It's obviously that I had positive pressure at the crankcase.



EDIT: WTF?? I read now on several forums that this situation is normal during boost leak test.

 

Is your manifold falling off maybe?

 

No I took it out ,is perfect.

 

Guys I found a 2nd huge leak. It was in the external. All of the air were escaping in the exhaust outlet. Time for a new one. And it was a ******* tial. :(