Best safe than sorry 
Keep up posted!
So some feedback from H111 - its ‘pinking’ very slightly at high revs on full throttle and the fueling is creeping towards rich. They inspected the plugs and found that there were three white plugs and one dark brown plug. They have checked the chargecooler for leaks (water might cause this), inspected the bores with an endoscope and all looks okay – including sealing at the head gasket.
The only oddity was that the three pistons with the white plugs had some unusual staining across the top of the pistons of each cylinder. The cylinder that had the dark brown plug in it had no stains on the piston. They think its a fuelling issue somewhere – causing there to be uneven amounts of fuel to be delivered to the cylinders or some kind of contamination of the fuel that is entering the cylinders.
First port of call is to clean and test the injectors, however they are concerned also in the fuel delivery, so they will confirm injectors are operating correctly at high speed on the test rig and check fuel pressure as we may be dealing with a blocked filter in the tank. One option may be to drain the tank and inspecting the contents.
They will do that tomorrow and see where we are…
Although I am disappointed that we have these issues, it may be that I prevented damage to the engine by going for the EMU, as it may have been fuelling wrongly with the stock ECU - it still had 265hp on the ‘before’ run - but at high revs it was losing power…
Mixed emotions I imagine, though I’ve been here before on other cars - in a way it’s a relief that a tangible issue has been identified. Like you say, who knows what long term damage you could have caused by continuing on blindly!
Fingers crossed it’s something simple, keep us updated 
The two will go hand in hand. The pinking or pre detonation or knock will be monitored and the ECU will try and do some corrective actions ( knock correction ) and probably pull some advance on the timing. This in turn will reduce the power.
Glad its been caught. No one likes a deformed piston due to det.
Injectors ok… no leaks from charge cooler - next step is to check coil packs - and potentially drain the tank to make sure there is no contamination… so not sorted yet…
Not so great news - compression test noted some anomalies, and it seems I may have a ‘gradual’ HGF which would only show up when trying to finely map fuelling. There was some coolant, and evidence of coolant burnt off around the valve seats. On the other hand, I may have prevented serious damage to the engine by deciding to move to the EMU when I did…
More investigation taking place with a leak down test today to double check compression
crikey mate, keep us posted - like you say you may have just saved/prevented a whole heap of cost and heartache.
That would now be two people I know with recent HGF on a 2ZZ… might start shopping around for a VHPD setup 
This isnt all bad news. The HGF is the weakest part of the chain so hopefully its just a minor issue with a cracked ring on the HG.
Yeah - I hope so too… I did read that the 2zz can suffer HGF due to liner issues on higher mileages (I have 58k) which I’ll be honest I am very worried about as that could be very costly…
Do they reportedly crack liners?
No liners in a 2ZZ IIRC, it’s some microfilm lining I believe which makes repairing/boring out very difficult (if even possible?)
I think you are right…
seems on 80K plus mileages liner cracks can cause HGF - but I am less than that… but yes… that’s what I am worried about…
Its this statement from a 2016 thread on ‘sleeving’ a 2zz that worries me…
‘The MMC structure is stronger and stiffer than the base Aluminum and therefore is important in sealing the head gasket’
Leak down test results…
Cylinder 1 - 28%, 2, 3 and 4 - 5,5 and 8%
Head coming off to see what’s going on
Oh wow, that’s quite a difference - just glad you’ve hopefully caught it in time before anything too awful happened… Let us know what they find!
Ouch. Be interested to see the outcome! Hope its a simple fix for you
Could be a new short block, or even new/recon engine 