It is debatable (sp?), whether the Skyline block is stronger than the 2J. But then it depends on so many factors what engine will be stronger, and who would tune an engine when stock internals become an issue ? What I mean is, if 1300hp is when internals have to be uprated, the car wouldnt be drivable, and nobody will tune to that level really.
Really, Id only tune to about 800hp MAX, so both engines will be fine.
Just my 2hp
