Join Date: Aug 2008
Location: Portland, OR
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Its really an academic discussion - the Gen III heads are more closely related to a true hemispherical chamber, especially when you compare the in-line valve layout in a wedge-shape chamber that the other makes use in their pushrod engines.
The fact is a true hemi head has a lot of quench area that would allow incomplete combusion and wouldn't pass emissions standards that was an issue in the early 70s and is the case today as well.
Today's Hemi shape is flattened out a bit more and we have an "open" combusion chamber that is a cross between a pent-roof and hemishperical shape, but we still have the dual rocker shafts and opposed valve layout...that to me is the hallmark of the HEMI head layout - the opposed valves and their ports make for an efficient layout.
GM's 2-valve heads (pushrod engines) only approach our power output by increasing discplacement...the GM 5.7 engines didn't go beyond 350hp and then GM went to 6.0-6.2L and beyond for more power.
The Mopar Gen III heads breathe well in stock form and we see net crank HP and torque values and MPG efficiency you'll never get with the older designs.
2016 R/T Scat Pack 392 Hemi Shaker 23Y pkg (6 speed MT) ordered 8/28/15, born 10/23/15, home 11/20/15
Torred / Ruby Red/Black leather
2009 R/T 27J pkg (6 speed MT) ordered 7/17/08, born 10/23/08, home 11/13/08
Hemi Orange / Dark Slate/Light Slate Gray leather