It seems that when the question "Why did my rod bend?" pops up around here, a lot of people would immediately point blame in a specific direction: turbo, fueling, tune, etc.
That's not very satisfactory troubleshooting to me.
I'd like to nail the culprit down as best as I can so I can find out where the responsibility lies and avoid a similar circumstance in the future.
It seems to be common knowledge around here that these engines have a tendency to bend rods when there is "too much boost too early" --- this has never really sat well with me, as it's just too over simplified an explanation IMO
Clearly the trouble there is with cylinder pressures rising faster than the rotating assembly is "willing" to rotate as the burn progresses. At some point the pressure wave overcomes the spontaneous combustion point of the remainder of the mixture, and detonation follows.
Is a little detonation enough to bend these rods, or is it pre ignition induced by the resulting temperatures from detonation that is the end culprit? Is preignition at all common in these engines? Most likely sources of the hot spots?
In my case, I do not see any of the obvious signs of detonation, although I do not have any reason to believe it had been an ongoing problem.
I'm not an expert, but I have dealt with detonation in the past enough to have a relatively good idea of what to look for. There's no deposits on the plugs, no pitted aluminum, no damage to the crown or combustion chamber, fire rings looks good, etc. Everything looks good.
Carbon buildup on the piston with the bent rod seemed quite acceptable to me and was no different than the others. It did have a slightly whiter tinge than the other cylinders, indicating possibly higher temps in that cylinder. Valve deposits/buildup seemed the same as all of the other valves.
It also appears that people tend to think that running aftermarket rods will allow the "safe" use of a configuration that would otherwise damage stock rods (ie a 19t with no more worries about too much boost too early)
I can't really accept that as safe practice --- So now the rods won't bend, but how about ring lands and rings, etc?
On my last and final log I did a few WOT pulls from a standstill, and then a few minutes later at light/moderate throttle driving, I noticed the bad noises and headed home with a light foot.
I started with a very conservative initial tune, and went through probably 6 rounds of tuning and logging over a 7 day time frame. Wideband o2 showed good AFRs, etc all the way to the end. Everything appeared good.
On the last round, I was advised that TCV duty cycle was set to 100% from 2580 RPM on up.
I don't really know all of the ins and outs of tunerpro or how to view the logs in great detail, but they seem to indicate that
Around 2800 RPM, 9 psi
Around 2950 RPM, 13 psi
Around 4000 RPM, 20 psi
By 5 psi, AFRs were 13:1, by 7.5 psi 12.5:1, 9 psi 12.1:1, 13 psi 11:1, and not long after about 12:1
This was on an engine that was in pretty darned good health. 110k miles, solid reliable daily driver on stock turbo w/ ARD green, no oil consumption or leaks, never any CELs
At the time of the "event" It had just been converted to a 19t, bosch 968 green injectors, 3" DP, do88 drop in intercooler, r manifold, etc.
So, who would care to comment on why the rod bent and how I can avoid damages of this nature in the future?