Does anyone know if the F23A and F23A1 engine performance differs. Had F23A1 swapped out for F23A and the US F23A feels stronger via TQ and HP. Anyone know why and are they equal in performance specs? Does F23A engine needs tuning for US climate and weather?:

thanks!

 

I would expect both engines to perform similarly. A1 to A4 is only a 2HP difference(not noticeable). AFAIK, the USDM 'A1' variants tend to be the same as the JDM 'A' engines.

A few things to verify.
Timing belt is correctly installed
Plugs are new and not fouled
Gaskets on intake/exhaust manifolds properly sealing,

Only thing that might cause an issue is when the engine was swapped, rather than simply replace the engine long block(head/block) the intake and exhaust manifold along with all the sensors were re-used. JDM ancillaries tend to be slightly different from the US ones. Make sure that you have reused all the components from the original A1 engine on the A engine. Including any thermo sensors and distributor. There may be a faulty sensor on the A engine or it may give a reading that is not quite kosher for the A1 PCM.