[aerohead]

At 80-mph ( not uncommon and actually legal in parts of Texas ) the SAE discovered that any benefit of small displacement is virtually lost.At lower speeds,there was definitely a correlation between displacement and MPG,however as speed increased,that advantage disappeared.I believe Chrysler credits there current system with a 6% mpg improvement across the board.And I believe the 8-6-4 engine used Eaton valve"enablers",which were plagued with problems,and that engine program was dropped from production.Removing pushrods could effect the lubrication system and top end lubrication.