im wondering if the b18c/gsr block with all stock internal would be able to hold the high rev of itr/ctr head? if it does i know it would mostly improve just torque but i would wanna know if it could operate correctly and safely for a daily?? my last ques is if a itr throttle body on a ctr motor would if and it would actully make a diff or would you have to get the intake manifold as well?

 

Stock GSR bottom-end with a ITR/CTR head would be fine. You will just have a lower compression compared to a GSR head. As for daily use if its done right then you should have no problems at all. The ITR(USDM) throttle body is 62mm compared to the GSR 60mm. You wont see any gain from that, So you might as well just get a after market intake manifold.

 

IIRC, the ITR only revs 200rpms higher than the GSR, so I'm sure it's fine. The only difference in the bottom ends of the B18C1 and C5 is that the crank on the C5 is balanced a little better, and the pistons of course.
I have no idea about the difference between the ITR and CTR top ends, as the ITR already uses the B16 head casting.