I thought you guys might find these two videos interesting. I've had intermittent ping/knock in the S60 under load. A bunch of us with the new 4-cylinder engines have experienced it and Volvo has yet to provide any help beyond telling us to use higher-octane fuel. (I already feed it 93, which helps compared to the ethanol-free 91 octane I was using but hasn't entirely resolved it.) I think it's a spark and boost mapping problem but I figured it can't hurt to pull the plugs and borescope the cylinders. The plugs looked fine (other owners have seen damage up to and including ejection from the engine) but I thought I'd show you the video. For comparison I have a video from my V70 that I shot a couple of years ago just because I had a borescope and it needed new plugs anyway. First the V70's 3.2L naturally aspirated and port fuel injected inline-6 and roughly 90,000mi on it (with a completely wrong date stamp): Next the S60's 2.0L turbocharged and direct injected inline-4 with 12,500mi on it (and another completely wrong datestamp): Unfortunately you can only see the piston crowns because I haven't figured a way to get the right-angle mirror into the cylinder and back out again. Still, the differences are interesting. You can see a little buildup on the old 3.2L engine but you can see a fair amount of bare metal. With the newfangled turbo-4, not so much. It appears to be completely covered in carbon of varying thickness. There are a few shiny spots where the carbon failed to adhere or, I think more likely, was blasted off by detonation. You can also see the spray pattern from the fuel injector. Interesting, no? This level of carbon buildup on the pistons seems pretty common for DI engines. It can't be great, though. This plus all of the carbon that collects on my exhaust tips also illustrates why we're going to start seeing particulate filters on DI engines in the very near future. Nobody wants to breathe what's coming out of these things. I might try again with the 45 degree mirror if I can find a way to make it fit though the tight spark plug holes. Carbon on the pistons is probably less important than carbon bulding up on the valves.