In the newer ones, last I checked they came with the 2.2 5S-FE...a stroked 3S with the same economy head. Switch the head for a G (instead of F) and put a few more lbs of boost on there for easy fun

Remember, as of 2006, Toyota's fastest vehicle IS in fact the RAV4. Although its bigger in all specs, they DID cram in the 3.5 V6 in there, so surely damn near any 4 banger will fit