new 2.5

[auto trainy]

Does the new 2.5 four have timing belt or chain?

[Mike Gerber]

I believe it has a chain. The 2.4 in my 07 has a chain.

Mike

[Brian R.]

The new 2.5 L is a 2AR-FE and has a timing chain. Mike, your engine is a 2AZ-FE.

Here are the differences I've found out:
Both the bore and stroke are larger on the AR.
The pistons in the AR feature a lower-tension ring package and additional cooling from oil jets.
A variable-output engine oil pump is used in the AR to minimize horsepower losses.
It also has a higher 10.4-to-1 compression ratio
The AR has dual Variable Valve Timing with Intelligence which allows the ECU to control the advance or retard of both the intake and exhaust cam timing. This is reportedly the same as having two adjustable cam gears instead of just a single adjustable gear on the intake cam.
The AR also has a variable-length induction intake manifold (ACIS) which provides both a long and short runner intake path to the cylinder head intake port. This allows for low-RPM torque improvements with high-RPM power enhancements.
There are something called tumble control valves which have been added to reportedly improve cold engine emission levels and heat up the cat converter more quickly.
The valves in the AR are now linked to the cam by roller lifters. This lowers the valve train friction.