What are your thoughts on wear from momentary knock during tuning?

[Sogono]

By just bringing up the subject of knock I realize I'm opening a conversation that's been had more times than can be counted. AND I know I'm inviting opinions with this question. But I genuinely want to know what folks think about the impact of brief knock events that occur during tuning.

While tuning, we're doing pulls, looking at logs, making changes, and repeating. Sometimes, those changes work, aaand sometimes they don't. Recently I've been experimenting with raising my boost levels, which has occasionally resulted in some fairly significant knock retard. Usually instances of ~3 degrees, but there have been a few of pulls that have shown me moments of as high as 10 degrees.

So, even though we're out of the throttle ASAP when that CEL lights, the fact that it lit means that there were knock events, albeit for maybe a second. My question is, how do those collective seconds add up? Are 12 pulls where you see excessive knock for 1 second equal to 12 straight seconds pinging away at WOT? At what point do you begin to wonder if your tuning and testing threatens the integrity of your engine?

I appreciate your thoughts.

 

[curt-s]

That's the fun thing about metallurgy in an engine. The older an engine, the more likely it is that any instance of knock could break rings, ring lands, or worse, as the metal continues to tire and fatigue.
Heat and the pressure wave are constantly changing variables, they're rarely the exact same way and even less likely the same exactly in succession. Smack once in a while, you're probably fine. Keep smacking it over and over, and it fatigues faster. Exponentially increase the heat and pressure by pusing the envelope, and now you're playing with an even bigger fire. Even though it's all a guessing game as to when, the general consensus is the chance that you're going to break something increases non-linearly the more successive the instances of knock are.

Keep tuning that engine for the breaking point over longer periods of time and sooner or later it's only going to take that next occurrence to break because it's already had enough of your shit.

What that line is? Nobody knows. It's a risk we all take.

 

[Sogono]

it's only going to take that next occurrence to break

So is it your opinion that failure from knock is something that happens spontaneously and not-so-much over time?

I've made the decision to drop back to near-factory boost since I don't have any hp goals, but I can't help but wonder if there will someday be consequences from the attempts I've already made. I suppose there's no way to know until it happens, or doesn't.

 

[curt-s]

So is it your opinion that failure from knock is something that happens spontaneously and not-so-much over time?

I've made the decision to drop back to near-factory boost since I don't have any hp goals, but I can't help but wonder if there will someday be consequences from the attempts I've already made. I suppose there's no way to know until it happens, or doesn't.

That's not what I said, no.

What I said was over time, possibility of failure from knock increases due to additive fatigue. Whether from earlier occurrences of knock, or just the hard life that a turbo'd engine lives with respect to heat and pressure cycles.

The likelihood increases the more you "re-tune" an engine as you're always pushing that boundary and one such popular way is to push until you find significant knock then back down a bit. You keep poking that bear, though, and she'll bite. That's true of old and young engines.

However, there's always the possibility that, regardless of age, that one "super" knock causes you an immediate failure. That's a random event none of us can control.

Spontaneous failure due to knock is more attributed to age and/or how many times it's been pushed to the limit, whether by being re-tuned at the ragged edge or just run hard through most of its life.