Hi guys,

Been on the forum for some time, browsing and reading alot...wanna gather as much info as possible before i start modifying my car (E8 MR JDM).
I know that too lean AFR's can lead to knock, but can too rich AFR's also lead to knock?

 

Yes overly rich afr's can also cause knock.

 

it can cause knock. It can also saturate the cylinder walls with gas and prevent proper oiling as well as fuel mixing with the oil.

 

hmm....what sort of AFR's would tend to cause this high AFR knock? values less than 10.5 maybe?

 

10.5 AFR is very rich..

 

i have had my AFRs @ 10.5 and have seen no knock.

maybe richer.

 

rolly1818, when ur car was stock what afr's did u see?

 

stock evos run richer than 10.0 during wot... thats as low as my gauge reads

 

i saw 9.8 after an exhaust install.

 

Yes, excessively rich AFR's can and will cause knock. But we're talking AFR's well below 10.0:1 in most cases. Not to mention "Bore Wash".

 

I was running 10:1 afr's and it was causing knock in the higher rpm range even after retarding a good amount of timing. Now with closer to 11.3:1 no more knock.

 

One thing that wasn't mentioned is that rich knock looks different than lean knock. Lean knock tends to result in strong knock spikes where as rich knock tends to come on slowly over several hunderd RPM and stay at fairly low levels, usually a knock sum of 5 or less in my experience.