If you had a mint standard one (ie not a 20 year old half rotten head gasket) it would be perfectly reasonable to expect it to be reliable with 500bhp on an unopened engine.
But they are getting old now, so a bit like a YB really they wont take the power they used to before something lets go if they are an engine with 20 years and 150K on the clock.

I bolted a GT35R to one and it went really well (felt roughly as quick in the same car as my old vauxhall engine on low boost, which made 457bhp) so definately in the 400-500 sort of ballpark.
But the head gasket was rotten so it didnt last very long, then the pressurised gasses from the head gasket going appear to have contributed towards the oil pressure relief valve seizing, and when I fixed that not many miles later it ended up with not compression so I guess the lack of oil pressure has killed the tensioner but not had a chance to pull it apart yet as got a couple of other projects which are more urgent.

Did quite well for what it was though considering its age and the size of the turbo I strapped to it!


I'm going to just give one a quick freshen up with new gasket and check the chain and tesnioners over etc and give it another go at some point.