Guys,

I hope someone out there can help me fill in the rest of the blanks. Christmas day I was out playing in the hills here in So Cal with my 06 AP2. Everything was running fine until I had to stop for a light. All of a sudden a loud clanking noise started coming from under the hood. I immediately pulled over, shut it down and checked the oil. Level was good ( i had just changed it about 100 miles prior). I was pretty far from home and without my phone so I decided to drive it a phone and hoped it wouldn't get worse. It actually got better and became barely noticeable. I decided to head for home. It got loud 1 more time briefly then immediately quieted down. there was still a noise but it was pretty faint and sounded like a playing card in a bicycle wheel (i've seen other posts with this same sound and it's usually the timing chain tensioner, that may be part of the problem, not sure). So I get home and it's running fairly well. I shut it down and start looking on this forum ideas. The closest I could find was an issue the 2000-2003 cars had with a faulty oil jet in cylinder #4 which caused major scoring on the wall. In fact the sound was exact. Armed with that info, I removed all the spark plugs and ran my barescope into the cylinders. #3 was very scored on the exhaust side and looked like some of the grooves were pretty deep. The piston head also looked like it had a small chunk missing at the edge. #4 was slightly scored but nothing like #3. #2 and 1 looked clean. Next I ran a pressure leak test and found that 3# was leaking at 60% and the air was coming out through the dipstick shaft. Looks like a new short block is in order.

Before I replace the short block I would like to know what happened. Have there been any reported issues with the oil jets in the AP2? What else should I be looking for as a cause? Could my last trip to the track have been the beginning of the end? A month ago I was at Cal Speedway running the Roval. After the second run I decided to check the oil and noticed it was a quart low (not unusual I hear). I added oil and continued. The next day I checked it more regularly and throughout the day added at least another quart. When I returned I drained the oil only to find it was black (burnt?). I have been running 5/30 since I started tracking the car without issue (?). Amsoil was in the motor at Cal Speedway. Did my lack of attention letting the oil get so low at the track cause this problem I now face?

Thank you

 

Are you the original owner? Sounds like some damage was already done if you were properly maintaining the car before you took possession. But you're on the right track. Scored cylinder walls could have something to do with low oil you saw. Curious to see the condition of the bearings as well.

 

I am the original owner and have followed all maintenance schedules. Usually more than what is required since I track the car. I failed to mention, the car has 14K miles on it and a Kraftwerks high boost supercharger was added 4K ago.

 

May have been the cause.

I recently replaced my block as 3 cylinders were scored due to piston ring failure. I was running high boost with my Vortech SC. Never had a knocking sound but oil consumption increased and white smoke emanated from the breather filter.

 

Did you go with a stock short block or have someone build you one?

 

I replaced the short block with a new OEM Ap1. I plan to keep the car NA.

The original block was OEM and supercharged for roughly 70k miles.

 

That sucks. Without the supercharger, AHM might have warrantied it. Then again, it might not have happened without the SC.

What kind of tires were you running at the Roval? If you were generating high lateral g's with sticky tires, running hot because of the SC, and were low on oil you could have starved it.

When I was asking about FI track S2000s, people said that they keep the oil topped up and add oil coolers and pan baffling to reduce wear.

https://www.s2ki.com/forums/index.php?showtopic=749717

Also, who did your tune? What were your A/F ratios?

 

Based on this short summary, I would suspect that the cylinder suffered detonation (chunks missing?) and cracked a ring land, leading to the cylinder wall scoring.

Did you see any scoring on the other cylinders? It probably goes w/o saying that you should see none. Did you see any detonation damage on the pistons?

Did you have much carbon built up on the tops of the pistons? You should, otherwise... you probably are running lean.

 

It is starting to look like detonation may be the culprit. There was a chip on the side of the piston and it looked like some metal buildup on top (perhaps part of a ring?). The car was just towed to a shop in town that does custom fab work for race cars. he will diagnose the problem and we'll decide on a course of action once we know what happened. He suspects it was in the tuning. We'll see but it makes sense based on his description and why it could be the cause. If this is the cause, I'll probably have him rebuild the short block and reduce the compression to 10:1 and have it custom tuned. He says I will ultimately get more horsepower with lower compression because the boosted motor is a bit more stable for the tuner to manage. I'll also change the sleeve material to a ductile iron, probably by AEBS. Any suggestions on pistons, rings, rods etc.?

 

definitely sounds like detonation, it's the only thing to cause chunks missing out of the head or block. Running one quart low in high G racing situations is taking a real risk, but that may have been a result of the detonation , but it is hard to say.