[olddog]

From my perspective a high performance engine verses a factory family car engine is a double edged sword, from a reliability point of view. Typically a good builder improves the oiling system and puts in more durable parts (likely to balance it better too). So the rotating assembly should be much stronger to take the intended abuse.

On the other hand, to get more power, more radical cams, with higher valve lift, are used. Then stronger springs are needed. I have seen radical racing setups that they loosen the rockers in the off season or just change the springs out each season. Letting an engine sit in one spot over the winter leaves a couple valves open. That is a long time to keep a spring compressed. From my perspective the springs are taking a beating over time, not miles. Now that assumes it is not getting revved up until the springs are dancing violently, which can take its toll in minutes.

So, I generally worry about valve train stuff the most. The more radical, the more concern. That assumes that everything else was done well and there are no issues with fuel washing down cylinders.