Will somone explain to me why the Jdm 4age is more powerful. IM going to do a motor swap on my mk1. Is the jdm worth the extra money?

If it's anything like the JDM 3sgte vs the USDM 3sgte...

The JDM motor has more power because it's tuned for japanese gas :)

So if you try and meet those same specs running on, say crappy arizona octane, you're going to be disappointed.