Question about changing AFR to prevent knock

[Tiny99]

I have a 2009 AWD 300c and I use the 91 perf cai tune with 91 octane fuel.
I have tried about every kind of 91 octane fuel that is available and I get about the same results everytime. Here is my issue, if I load up the 91 tune and leave it as it is, I get about 2-3 st knock at wot 3800 rpm and up. If I set the AFR richer (12%/14%/14%) I can get it down to an occasional 0.5 st knk.

For kicks, I tried 94 octane fuel and I still needed to add 4%/8%/8% to get it down to zero knk. The stock tune doesn't knock

I do not mind having to set the AFR richer, but I wonder why it is required? Should I consider this normal? Since the car is AWD, maybe the additional grip is loading the engine and causing knock? Is this affecting the gains provided by the 91 perf cai tune?

I know that I need to get a wideband and figure it out myself. But I thought maybe someone already had that kind of issue and could spare some info...

Thanks!

[mikel]

the extra load from AWD may well be the case, we dont have an AWD dyno, thus we never tuned them here in person...

[Tiny99]

Ok, thanks for the answer...
If we presume the load from AWD is the issue, what would be the best way to fix this? Fattening the AF or pulling the timing?

Thanks!

[amw]

I would reduce the timing by a degree and see if that does the trick.

[mikel]

agreed...