Is upgrading pistons and rods mainly just for strength. I know pistons can change comp ratios. i would like to build up a vq35 and wonder if I would really need them to accomadate they tomei cams.

 

There is no need to upgrade the vq35 pistons or rods to accommodate Tomei cams. If you are are going to upgrade anything along with the cams, I would do springs and retainers but even that is not necessary depending on the specific cam chosen.