Compression difference

[old-school]

Good morning everyone. Can anyone explain why there is a difference in compensation ratio between the 03-05 and the 06-08 hemi engine?
Thanks for your knowledge. This is the 05 and 07 specs from Alldata.
Clint.

 

[70chall440]

I could be wrong but I believe it is the heads although I seem to remember something about a piston change in there as well.

 

[69Bee]

The engine features a displacement of 5,654 cc with a 3.917-inch bore and 3.578-inch stroke. The unit is housed in a cast-iron block and it comes with a cast aluminum alloy for its head composed of 16v OHV design. The compression ratio of the engine from the 2003 to 2008 VVT model years was 9.6:1.

The 5.7 Hemi VCT follows the format of the former but with a few tweaks, especially on the cylinder head in order to improve airflow. It revises the compression ratio of the engine to 10.5:1 between 2009 and the present model years to augment thermal efficiency leading to an increase in mechanical energy that further translates to more horsepower and torque values.

5.7 VCT VS 5.7 VVT: What's the Difference between Engines?