Just lost another exhaust stud today. Replaced one that was missing a few months back, tightened everything up. Some other exhaust nuts were loose again.

Do I need to use bigger studs or some sort of thread locker? It's on a 1600 kombi engine. Is there a better nut/bolt/stud combo?

https://www.bolt.com.au/nuts-conelock-nuts-c-1010_1086_1194.html 

.......and new studs with "Screw Lock" (low strength).

I had an exhaust stud come loose at the Sydney VW Drags this year. I used a timesert with threadlock and it hasn't pulled or loosened once yet.

have you tried helicoils in them,we use them in the trade with great success?

As long as its not stripped, I can't see why a thread locking compound (as long as it cold handle high temps) could be used.

How loose is the thread in the head when you screw the stud in? Cos galvanic corrosion between the steel n ali along with the heat is pretty good at killing the thread in the head.

Either helicoil or time-sert are the best ways to fix unless you know someone good at TiG welsing ali