the alluminum has increased durability under boost and raised IATs. constantly cycling from vacuum to pressure at over 100 degrees has been known to cause early failures in plastic manifolds. my thing is i might want to mount something to the top of that manifold and metal is the only way to go there
. Personally i would rather use the stock manifold as you nevver know the runer design changes and the effect on the torque curve but the runners on the gtr manifold do look longer so it is possible i could see tourqe gains. i might even want to epoxy the runners to change the cross-sectional area and change the port design to match the port design of the VQlower manifold. another note worthy question would be do you think our manifolds due to the higher flow rating of the engine might be designed to where they could be used as a performance increase on an HR? just a thought they look nearly the same tho.