Originally Posted by vwbased

1. Possibly too much boost on a wimpy cast piston.

2. The second land can break before the top. It did so on my old B20's cast pistons without a hint of detonation. Just too aggressive of a tune. Postmortem of combustion chambers and rod bearings indicated no detonation.

3. Lean spikes can be indicative of missfiring which includes detonation. When a cylinder missfires or detonates, the oxygen is not completely consumed and the WBO2 gauge will read lean. HOWEVER, your lean spikes are occurring during shifts and so are not indicating detonation.

4. The black top land can also be an indication of detonation. Detonation can result in a rich combustion around the top ring land. Normal combustion tends to leave the top land clean. The usefulness of this tip depends on whether the engine has a lot of miles on it.

Originally Posted by joppe

Using crome free/pro you have too much ignition when high boost. I have logged with pro that ign map says 10, 8, 6 degrees and datalog still shows like 16. It doesnt pull timing enough. Somewhere fix for it but with crome gold it pulls enough timing. Maybe get ectune for better EMS. Im using ectune for my car and crome gold for other cars tuning.

Originally Posted by tagperformance

After taking another look at the top off the piston, i didn't notice any metal specs which are signs of detonation so i'm gonna have to retract my first diagnosis and have to say that it's improper ring gap. The rings expand during heat and if the clearance is too tight they will butt and pop the ring land out from the pressure. My apology guys.