In my little world, I seem to have noticed a pattern with Cylinder 4 in the 2.4 Ecotecs.

Block 1: Stock and boosted 2006 LE5 block, Cylinder 4 cylinder worn out bad (0.015" over spec)

Block 2: Built and boosted 2015 LEA block, Cylinder 4 has the lowest compression and worst leak down result

Block 3: Stock never boosted 2012 LEA block, Cylinders 1-3 measure 0.0006" wear over spec, Cylinder 4 measures 0.0010" wear over spec

Could this be a problem with block cooling around Cylinder 4? Anyone notice something like this?

 

it's been known since 05 that cyl4 runs hot. it's at the end of the cooling chain.

 

If my analysis is correct:
Out coolant pump -> Cyl 1 water jacket -> flow across Cyl 2-3-4 water jackets (some leakage through head gasket) -> up through rear of Cyl 4 -> Into Cyl head at Cyl 4 -> flow across Cyl 3-2-1 -> Exit head at Cyl 1 -> back down into block near Cyl 1

A possible cure I envision is to plumb a restricted hose from the outlet of the water pump directly to the Cyl 4 water jacket at a strategic location to give it priority cooling with the coolest coolant, that might be cool.

 

 

I don't have any historical measurement data to look at this objectively which would be the only way to confirm there is an issue here. Block 1 and 3 got measured after disassembly, Block 2 is a new build and has low compression on Cyl 4. Block 2 would need some tear down to see whats up with 4, maybe stuck ring from diy groove sizing? ring seating issue? overheating problem?

 

I feel like the only way to really tell would be to build a new engine and record all the measurements, then run a certain amount of miles of how you would normally drive the car(maybe 10k miles), then tear down and remeasure. Putting thermocouples in different areas of the cooling circuit during this testing would probably help prove your case. Either way, its an interesting thought.