Hey guys. I recently purchased an 03 G35 sedan 6 speed. Rod is hanging out of the block. Im buying a vq35de with rod knock out of a 2003 G35 coupe 6 speed. Ive researched for hours and cannot find a definite answer to the 20hp difference in these motors (260hp vs 280hp) The engines going to the machine shop to be rebuilt. Id like to know what differences these motors have so that I know if I can use the coupe heads or know if I should swap my sedan heads on. Ive heard of exhaust differences, ecu tuning, cam differences (although i read someone matched part numbers between 350z cams and maxima cams) Anyway, does anyone know what really makes the hp difference? Heres my G btw:

 

There is no difference truly. The numbers were only "higher" for the coupe to sell more coupes and make coupe buyers feel better about paying $8k more than a sedan.

The only difference you MAY face would be whether or not your car and your new motor are from early 03 or 03.5+. There was a slight ECU harness change I believe. The engine should be the same, but how it hooks to the ECU may be different, cuz I know you can't etune an early 03, but you can with an 03.5
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It wasn't the harness on the 03 sedan, it uses a totally different ECU. That's why Osiris isn't compatible but there are members that found a standalone tune that worked IIRC.