about 8 years back when i had my 1st of many t-vans, i thaught it would be cool to do straight 3" (un-educated then) needless to say i blew my 1st headgasket a week later from instant boost cut. i would say if you restricted it some how or ported the wastegate hole you'd be good
You didn't blow the HG because you were getting boost cut out, you blew it because the HG was old.
From what I've heard, you will go into cut out. I never did, even without running a down pipe, but my mitsu was kinda trashed.
If you've got a good running engine it can handle 14psi+ from the mitsu. If you get a 3bar cal, you'll have fuel and you can run that mitsu to it's 18-19psi limit. Or you can hog out the wastegate and port the turbine housing. All of which is a waste of time on a mitsu turbo IMO.
I put a full 3 inch exhaust with a cat and muffler on my van with the stock turbo and I did get a lot of boost creep on my low boost setting. The low setting was the boost nipple from the turbo going directly to the wastegate. Stock exhaust showed about 5 psi, with the 3 inch exhaust it spooled to about 7psi and did the creep to about 10-11psi. Actually I did not mind a little extra boost or the bit of creep, the 5psi was a little too mild for my daily driving habits. On my high boost setting which was 17 psi through a grainger valve I did not see any boost creep. Although without a cat and muffler I really don't know what would happen.
Three ways to deal with boost creep. Restrictive exhaust (which is what the factory did), bigger wastegate, more fuel. On a TD more fuel above 15psi requires a chipped computer to handle a bigger map sensor.
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