Quote: Originally posted by crono33 on 02 March 2004
there is a misconception here. knock sensors are there just as a safety feature, but they never prevented engines from getting knackered by severe detonation.
moreover, it takes a lot to make a NA engine to ping enough to get damaged, and this tells a lot about the quality of some aftermarket chips.
also, pinging can occur in just one cylinder, due to uneven mixture distribution, faulty injector, faulty spark plugs, faulty valves etc.
actually, when knock sensors detect knocking, it is often too late.
if knock sensors were so good, ECUs would simply r****d until detonation started to occur then back up a little. unfortunatly is not so, therefore the maps must be conbservative enough to allow for some crappy fuel or other thing to happen without destroying the engine. many aftermarket chips are notorius for destroying engines, expecially turbocharged ones.
they were probably written from a comfortable desk making a lot of assumtpions and little tests.
as i said, knock sensors are far from precise, and can get very confused by engine noise and vibration that occur at high rpm, where knocking can be really destructive. in fact, most of the tuning firms use a mike and headphones plus a skilled operator to detect pinging when setting a car on a rolling road.
another thing to keep in mind is that pinging can occur at different levels of severity, and that there is something else called pre-ignition, which can really destroy any engine in seconds and which has completely different causes.
so when engine damage of that type occurs, an investigation should be done.
broken engines is just one of the consequences of homemade tuning...
Some valid points, and generally along the correct lines, but a tad muddled up.
There are typically 4 not good ignition characteristics.
In increasing severity:
Pinking (not pinging)......a slight metallic noise you get. Usualy caused by ignition too far advanced and the piston rattling in the bore as it goes over TDC. Nothing major and the engine can live with i for longer than you think. Easiest solution is a higher octane or r****d the igntion.
Knock, a dull thud caused by 2 flame fronts colliding from accidental ignition of mixture away from the spark plug. Harder to diagnose as it can be hot sports, mixture variations, carbon depostis, lean spots, ignition timing. But best run a fuel that can resist knock, and RON is what we use to provide info on the fuels ability to hold back knock.
Pre-ignition, the auto ignition of the mixture before the spark is even present, so ignition timing isnt always, or rarely is teh cause. Almost always caused by a hot spot, either a plug that doesnt shed heat fast enough, a hot exhaust valve, carbon deposits that glow. But the heat is mostly caused by incorrect timing, so again, it can be solved by sorting ignition timing (conused? lol). But sorting mixture, timing and plugs usually sorts it.
Detonation, very similar to pre ignition, but wholitically more violent and instantaeous. Akin to an explosion rather than an abnormal burn. Difference is that it typically occurs after the spark has arrived
The sensors in engines are specific, each engine will give out a different frequency and the sensor is built to read that frequency. The knock sensor in the F4R will take action before any damaging problems start.
Possibly your piggy back ECU would have affected it since it affects input signals to the ECU.
Most RR operators who do look for knock use an automotive steathoscope since the engines they work on dont have a knock sensor, and you kneed to know the knock/det frequecy before yuo can fit your own knock sensor....so its easier just to listen.
There is alot of talk about making spark plugs aware to combustion abnomalities by monitiring the ionising voltages and resistances. By doing so, they can monitor each cylinder and each burn.
