The 5.9V8 pistons withe the oval soap dish increase “tumble” ( or barrel motion )
The original flat top 5.2 pistons probably had superior squish jet effect.
Original 5.2 pistons seemed to be slightly less than 20 thousandths in the hole
5.9 pistons seem to be slightly more than 50 thousandths in the hole.
The 5.9 needed a custom cylinder head design.
It was all about the NOX, no other reason for the 5.9 to have that dish, a KB107 style piston and about .035 piston to head clearance would have been perfect.
“Fast Burn” does slightly decrease NOx, so yes a “oval racetrack” shaped cavity that concentrates “Tumble” would both reduce compression ratio, pinging, and reduce NOx.
The original 1994 iron V10 truck engine used those same 5.9 V8 soap dish pistons “as a cost saving measure” according to Willem Wertmann. I wonder which engine size had the lowest grams of NOx per mile ?
I suspect the 5.2 V8 has the best brake specific fuel consumption.
