Forged Redeye Engine Failure :( Why????

[16GoManGoHC2]

Some engine 101 diagnoses for those interested in learning.
I was asked by someone for my opinion on engine failure. These pictures tell tales.
Photos are of a set of billet main caps that were fitted to strong Redeye block. All premium parts were used, Callies Compstar Crank, Boostline Rods, Wiseco Custom Pistons, ARP Studs, etc. These main caps held down by ARP main studs pictured, One would think about a bullet proof rotating assembly right? Nope!! So what happened? The tell tail is in these pictures. Anyone care to guess what went on here? Tune was right on, was making over 1500 to the wheels twin turbo. Had multiple power settings in the tune, 1000, 1300, 1500. On 1500 it went BOOM. No detonation, no nothing showing bad in the logs, all was great then BANG, disaster. What is seen here? And what needs to be better next time and why? (Aside from 4 bolt main caps on at least the center 3 caps).

 

[vortecd]

Top cap in 1st picture was on backwards or notched on wrong side?

 

[BULL]

I'm seeing some fretting that on the mating surface that doesn't look good...

 

[Jack_Toepfer]

I believe the #1 cap in the first picture is just turned 180* compared to the others for the picture. I believe this because the tang witness mark on the opposite side is where it should be from the bearing in the block. If that bearing wasn’t lined up properly it would have witnessed on the same side of the cap as the tang slot, and would have been a quick catastrophe, not one that only exposed itself at 1500hp.
The hone marks on the caps lead me to believe the bore was line honed with these caps before fitting, that they weren’t just slapped in there. Ideally this was done with the appropriate hardware installed.
1500whp is pushing it, even on a “strong Redeye” block, ain’t it?
244-5400 is probably the right main studs.
Did Demon supply the other ARP hardware? Do they recommend stock hardware for the side cross bolts? I don’t see as much ARP lube as I would expect, but I imagine that was washed away with runtime.
I would have expected thicker caps on 2,3, and 4 not just 3.
I agree with Bull, not sure why there is anything on the mating surface.
I’m not convinced anything in these pictures failed