So im new to evo's and i just picked one up couple monthes ago i built the motor with wiseco 9.1 piston eagle rods stock head kelford 272 and stock turbo ive had car running on 22 psi for about 3k miles and im just using factory ecu reflash for tuning. long story short i pulled my head today cause my valves were leaking in #2 and after i pulled the head i discover cylinder #4 piston is missing chunk of the piston and has detonation on it but the other 3 look great my afr are normally 11.3 to 11.7 pump gas im running walbro 255 and precision 850 injectors on stock 8 turbo using bpr8es plugs .025 gap when my tunner tuned the car we never had any knock at all. can some one help me out here telll what they think?

 

Sometimes knock can show up on the street and not on the dyno. Could have been a hot day, or high engine temps. your A/F sounds fine but who knows, could have had a tad too much timing. could be a clogged or bad flowing injector too.

 

the logs show no knock at all this was street tuning and i had my injectors flow tested this is #4 first one to get fuel i cant figure out why this happened

 

Well, it obviously got hot. Tell the tuner to take out a little but of timing when you put it back together. In most engines, there will be one cylinder that is more prone to knock or detonation than others due to the dynamics/geometry of the engine externals (exhaust manifold, intake manifold flow etc..

And also, if you just picked up the car a few months ago, it could very well have been there before you bought it.