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the hemi is a thoroghly modern and efficient engine in cyl head design, and it boasts some advantages over in-line valve heads like the LSx and the 4.6L SOHC heads-- being a hemi (more accurately a modified pent roof), the valve moves AWAY from the cyl bore as it opens, reducing valve shrouding significantly. having this arrangement also creates a much better short side radius geometry.

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I'll agree that the new hemi head has been optimized/updated for modern vehicles. Yes, the hemi combustion chamber layout is good for large valve sizes with minimized shrouding, and therefore high-rpm breathing. Yes, teh MDS adds to MPG -- but so do the single and double-OD ratios in the trans.

I believe I read somewhere years ago that the hemi combustion chamber was the worst for thermodynamic efficiency, due to high surface area. It also has to have a pop-up piston to get acceptable CR (as a hemisphere has greater volume than a wedge), and that popup impedes flame travel. I'd speculate that it therefore is less tolerable of lean mixtures, which are harder to burn.

Perhaps that's teh angle that Pale Roader was referring to?

It would be interesting to see BSFC of a 5.4 Ford, 5.3 and 6.0 LSX, and 5.7 hemi - as-is, without MDS or other features. And of 4.7 vs 5.2 Maggie.

So did we decide on the original 4.7 installation question???