Join Date: Dec 2016
Location: San Antonio, Tx
There are several performance differences between the 04-05 and 06-08 for sure, but a significant number of them are in the intake and exhaust systems.
I have found documentation of the later engine having 1mm oversize intake valves, slightly improved cam profiles, slightly different dishing on the (same compression) pistons to accommodate said valves, and slightly thicker rods. Some also say the crankshaft was slightly altered, but I've found no proof of such. I have found no documentation (in English at least) of the innards of the K24A, how they differ from the A2, or if there were any revisions throughout the years. Keep in mind these engines we're all built in Japan. Were they upgrading just a small portion of them with new innards to ship stateside and making the rest with the older spec parts? I'd venture not.
Outside the longblock of the 06-08, intake piping, throttle body and plenum are larger. As is the exhaust piping, along with a better flowing cat.
With that said, I have an 04 with all of the 06-08 intake and exhaust parts. The difference is noticable. Once I swapped out my tired K24A2 for a JDM K24A, the difference was much more pronounced. My opinion is, especially for a car being brought to renewed OEM, the difference between the longblocks, and their power output, would be negligible.
Of course, this is my opinion, and if anyone can point me to proof that I am incorrect, I will gladly read such proof and if necessary amend my statements to reflect what is factual.