You left out a lot of needed information. Are you oiling through the pushrod? Are you using a 48 or 59 degree block? Are you using offset roller lifters? What heads are you using?

Let me tell you why I ask these question. Years ago, We ran "x" blocks with 59 degree lifter bores/early Arrington heads----I had to use 3/8" pushrods. But, when we went to "R" blocks with W7(or 8 or 9)heads this allowed me to use offset roller lifters and get a short pushrod(7.25"). 5/16" was fine for this application. Even the "big time" oval track builders(Arrington, Petty, Fyrar) used 5/16" pushrods until the small blocks got to 10K+ RPM. Then, they went to 3/8" and even later 7/16". But these pushrods were lightweight and usually came from PPC in Arden NC. I think now they use Trend pushrods.