ok, dont do foward facing cut n shut stock plenums, as rb2530 has stated about flow velocity and the disign on the manifolds from factory (with nissan spending millions on flow testing components and what not......) if u look at the rb20 manifold u will notice it is larger in the middle were the tb is located, and its acutaly not a good size at the end to put a throttle body, i looked at this last week as i wanted to do the same thing, a better idea i would think would be cut n shut the stock manifold to be directly opposite where it is now and put a 90 degree bend and plum it from there, as this wouldnt affect the flow in the manifold so much, nissan knows what there doing when they build a car, theres a reason reputable companys release things designed they way they are, and its not so someone can build a better designed peice in there backyard in 10 min, or even expect them to work half as good