I really don't think the main risk lies at over 5K revs. Let me explain....first of all you'd be risking a hefty fine if you use 5K in any gear from 4th to 6th and even in 3rd you can easily exceed the national 60 speed limit. The thing is that very few of us will use 5k for any prolonged period. No, the main cause of detonation would come by working the engine hard at low revs up long hills. It's all very well toodling along at 30 in 5th on a flat road on next to zero throttle but flooring it at such low speeds puts a massive strain on the engine and there's always the temptation not to change gear .I can remember back before the day actually asking my dad what that noise was climbing steep hills on our Sunday run out in Wales....pinking he replied, never really understood it until I got my first car.
Pete
That's also partially incorrect I;m afraid, while knock can occur at low speed/rpm, at under 5K the ECU and knock sensors will detect knock and retard ignition timing until such a time as its no longer detected for a certain amount of time (pre programed into the ECUs maps) then it will gradually increase the timing to the original settings, thereby protecting the engine form pre ignition.
Now proper detonation takes place when the flame front is preceded by hot spots which ignite the mixture ahead of the flame front, which is caused by either too much compression for the fuel octane being used and/or the ignition timing being too far advanced or retarded, now what you have to remember is that if you using low octane fuel the ECU is already retarded the ignition timing to reduce the knock that is already indubitably taking place, so its not going to impact the after 5K rpm/loads as badly as it would if it was not already retarded therefor protecting the engine from damage.
Not the best explanation but hopefully gets the point across.
Thanks TR, yes it did, it's surprising what is bandied about by so called experts.