I read this on Allpar but am not sure if this applies to the SRT or RT or Both...

For 2009, the Hemi engine was upgraded to get 5% higher gas mileage, and more power, especially at lower engine speeds for a better off-the-line feel, thanks to variable cam timing, an expanded MDS operating range, an increased compression ratio, improved port flow, and reduced restriction exhaust and induction. Other updates are crankshaft structural upgrades, a dual-mass crankshaft damper, floating pin piston design, valve spring design and oil pump capacity increase for VVT. (Again, manuals can’t use MDS — yet).

Any ideas?