Mostly from what I've gathered reading the engine failure thread over the years, is usually one of the following:
- turbo failure, ceramic exhaust wheel is jettisoned into the catalytic converter and ceramic dust makes it way into the cylinder bores via the exhaust valves. (it may have been mentioned by a builder or tuner that they've seen this happen 25% of the time)
- spun bearing, poor choice of oil or poor maintenance or not overfilling (sump emptied, resulting in oil starvation or due to no upgraded oil sump baffling) or just plain unlucky (or all 4)
- oil pump failure. limiter bashing (hard ignition cut). early short oil drive crank more susceptible to failure than the long oil drive due to smaller oil pump <-> crank surface face. Newish N1 oil pumps are considered junk (it's speculated that manufactoring process different from early N1 pumps)
- poorly assembled "built" engines that go pop easily. pays to have a engine builder who has built hundreds of RBs (red r racing etc), not a shop that is learning as they go on your engine. Personally I would take an unopened factory engine over an RB put together by a random shop.. common thing with "built" engines is bearing clearances completely wrong
- 100,000km service gone wrong. wrong belt tension (belt skips teeth and pistons meet valves), or balancer not torqued to spec and working itself loose (which the oil pump relys on) or even not bothering to do the full service and leaving the factory fitted tensioners etc fitted which then seize.
- Poor tune, especially Jap ECUs, often brought off ebay and put into cars without checking it on the dyno, especially Mine's... completely unsuitable for australian fuel/conditions