ClubWRX Forum banner

21 - 21 of 21 Posts

2003 Subaru WRX 'Sonic Yellow'
21 Posts
Discussion Starter #21
There are two ways we can approach this. There is the "normal operation discussion" and then looking at this from the perspective of "would it cause any harm anyway?"

Modern cars incorporated electronic fuel control, electronic timing control, and knock sensors primarily so that manufacturers could increase engine output, reduce fuel consumption without increasing risk of early failure. The goal is to minimize something called the "Brake Specific Fuel Consumption" or BSFC. To do that, manufacturers have to choose optimum spark timing that sometimes is very close to or beyond the detonation threshold at that particular load.Normal operation for modern ECUs at low loads is to constantly ride that line of detonation backing off timing when knock is detected. -2.11 degrees is the minimum step interval of feedback knock. If that is seen consistently in a particular load range, it's registered as Fine learn knock, then decayed over a certain criterion to zero.

If you are concerned, do some data log and look for where the knock occurs. If consistently under around 1.2 calculated load, it's not very concerning. If above, you should have further conversation with your tuner.

So, the second piece about "would it cause harm anyway?" Even if the behavior is abnormal, cylinder pressures under 1.2 calculated load are not high enough anyway to cause damage to components with mild detonation (mild enough for the ECU to only pull 2.1 degrees of timing). If knock sum values become very large OR the knock is registered at high loads where cylinder pressures are high, then you'd have cause for concern with regards to component lifetimes (pistons, bearings etc.)

My signature is a quote from Roger Penrose' book The Emperor's New Mind. Ultimately Sir Penrose is calling attention to the fact that our cognitive biases and fear of challenging the status quo of accepted science stymying further progress. Children OTHOH, are not bound by these biases and provide incredible insights when you least expect it. It's a good read -- I would recommend it. A lot of it is wishful thinking IMO, but look up "Orch OR" if you're interested.
Thank you for the very valuable info, glad I have been pointed in the right direction. I appreciate your insight
21 - 21 of 21 Posts