I've read about STi8 TMICs opening up between cooler and ends at higher pressures.
Is this common? Anyone had this happen to their car?
Can they leak without the crimping being visibly distored?

There is an worrying hissing when I'm on high (above 1 bar) boost...

 

I think this is for larger turbo/boost applications. In such cases you should be looking at FMIC's anyway.

 

I'm sticking with the TMIC, lot's of cars have and are being run with 330 up to 400 hp with TMIC, and I'm not doing any dragracing.
But it's the issue with the ic splitting up at down to 1,5 bar, and I'm running 1,4 normally and sometimes it spikes :-/

 

Had a talk with a semi-local rally tuner;
Yes, it happens and no it doesn't need to show...
Better get that IC welded...

 

Yes, it does happen. I opened mine up and re-sealed it.

Let me know the welding costs and results

 

Got the welded IC back and mounted it yesterday. No more hissing sound when I'm on high boost
I contacted a local metal workshop and he gave a ridiculously low offer, so I ripped out my IC and cut off all (abt 150 pcs) clamp lips and drove over.
The gasket was uneven, I suppose since I had the BOV flange welded. There's no way the ic could have been airtight!
Of course he had underestimated how much had to be welded, but still did everything for abt 40£
The tricky parts are along the intake flange and on the sides where there are lips holding the side panels, on the sides the welder have to melt down a lot of material.

Dirty where the gasket sat, but not so difficult to clean when the ends are off

The mechanic said cast alu is usually contaminated, hence the coarse welding. I don't care