Sorry to see what I suspected was true....
The Alta STAGE3 tune is just too aggressive to run with stock internals....I kinda suspected the pistons failed in this manner as soon as I heard you were running a stage 3......a couple of years ago, there was a few postings similar...and the first of the custom aftermarket pistons there were made of better materials came out.
Sounds like with some of the above info, you are well on your way to finding the right pistons if you plan in sticking with the current stage 3 tune, rather than switching to a stage2. Guess for most it comes down to $$$ events like this! Then again, it is folks willing to blow stuff up and then fix them that helps us get better products from the builders...both OEM (I hope) and certainly the aftermarket!
Good Luck again!! And PLEASE keep us posted with what you decide to do!!

 

Absolutely.

 

I think I'll go with the aftermarket pistons, but not 100% sure. I'll pick up the block in the next days and sent it to a local machine shop for a deep inspection and keep you guys posted.

 

Well, just spoke with the dealer, they gave me a quote and I have 4 options:

1. Rebuild the engine, with the dealer.
2. Buy a new engine and the dealer will install it.
3. Take the car to guy who is expert in BMW and tunning cars (very very recommended) and rebuild the engine with forged internals.
4. Same as 3 but with stock internals.

Option 2, it's 30% more expensive than the stock rebuild, seems a better option than a stock rebuild.
Option 3, look's like a great idea too if I want to add in the future a bigger turbo, cams, etc or stay with the Alta Stage 3 Map.
Option 4, it's the cheapest, like 20% less than forged internals.

With the forged internals I have in mind:

*Pistons, CP Carrillo 77MM Bore 10.5:1 CR. Or stock
*Rods, CP Carrillo H-Pro
*Bearing Shell??

Any advice?

 

Option 5, you could buy a used engine from a wrecking yard.

Stock JCW engines have a 10:1 compression ratio, you might consider staying with that, with the bigger JCW turbocharger it adds some longevity to the high performance engine.

Dave

 

I don't live in USA, there are some junkyards in my country but with probably only 10 JCW in my country, the chance to get a used one is zero.

Edit: I was checking the prices online, a looks like the rebuild will be 50% cheaper than a new engine, even with aftermarket internals.