Odd problem. If the engine is labouring after having been driven on the motorway, say, with lots of cool air, there is no problem. However, if I've been stood in traffic and then pull away in a slightly higher gear I can hear what could be described as loud pinking or, possibly, pistons rattling. I have forged pistons, been in that block for about 80K.
What is the most likely cause? How can I determine which it is for sure?