Looks like a lot more went on in that cylinder than just a cracked sleeve. Did it ingest something? There are deep dimples in the piston top like it smashed something. What did the bottom of the head and the valve faces look like? Up close does it look like physical damage or is the piston just eroding away. Erosion would be indicative of detonation.
There is also a good amount of scuffing all around that cylinder wall that usually occurs when a piston expands more than anticipated (from overheat or detonation) and contacts the cylinder wall. This could also be from insufficient piston to wall clearance or debris in a cylinder which goes back to the marks on the piston top.
You're correct, as this specific cylinder did, in fact, have detonation. Tuning with 93 went smooth, and the engine continued to make torque. The spark plugs were new, and nothing showed or gave any indication that we couldn't continue. In other words, it was "business as usual", as we came to a stopping point with 93 octane.
Problems didn't start until a few pulls into switching to E85. After checking plugs, cylinder #2
had white spotting on the electrode. Almost as if that cylinder was starting to starve of fuel. At first, we thought that maybe E85 dislodged something in the tank, or elsewhere, and was clogging the injector. We didn't want to rule out a faulty injector, as they were basically new with only a few pulls completed with them (ID1000's). Switching the injector to another cylinder did not change the results. Swapping them out completely didn't either. I believe another pull or two was completed while pulling a ton of timing, and our problem seemed to have disappeared for that run.
It wasn't until we pulled plugs again (we were pulling them after every dyno pull) that we noticed cylinder #2
was wet with coolant. Inserting a bore scope confirmed that we had coolant in the cylinder. Typically when a sleeve cracks, it's extremely noticeable in the exhaust, or just a "kablooey" type event. There was none of that in this example. Other than coolant in the cylinder, nothing gave indication of a catastrophic failure, but we knew at that point what had happened, and it was at that point that we put the car away, until I wanted to deal with it this year (now).
Below is a pic of the bottom of the cylinder head (cyl #2
). This is an extreme closeup, and the carnage is not that bad in person. The material is from the sleeve itself, being broken off in the cylinder. This will be de-burred at a machine shop, and milled appropriately.