You just answered your question about the Hemi (sorta...) heads. The dual plug modified Hemi head with two quench areas is much more compression-tolerant than the old Hemi, or most wedge heads. Its a step in a series of design choices. And a dash of marketing, too, but the Hemi does have some actual engineering advantages. There's no yawning chasm of superiority or inferiority compared to the GM wedge design, but all the little bits and pieces work together. The Hemi is also a lot easier to work with today since they put the cam so much higher in the block with the third-gen Hemi. The pushrod geometry, while funny looking because the pushrods are nearly horizontal, is actually a lot better than in the old Hemi or even a canted-valve engine like the Chevy 454. And the pushrods are shorter than a GM LS-series so the valvetrain mass is quite low for a pushrod engine.
Originally Posted By: artificialist
I'm surprised by the compression ratio. I'm not used to seeing 9.5:1 compression in supercharged engines without direct injection.