I think now-a-days people tell you that you can run ti valves on the street with DLC coating. Ti is sexy but I don't turn that many RPM's. I've always thought you could run alum rods on the street, just don't tell anybody or you're gonna have to listen to all their smack.
It is all about stress cycles, and whether those cycles are close to a certain limit. Some lawnmower engines have had aluminum rods. They live a very long life, due to very low stress. An example of a very low stress situation was i had a set of BME396 forgings made with 2.1 rod bearings, 7.1 inch long, .990 pin end. I built a 4.35. bore rb motor with a stock 440 crank offset ground to 4.00 stroke. Peak rpm was never over 6400, cubes 475. It lived a very long life, after i raced it for rwo years at about 600 hp and sold it i ran into the buyer years later, and he was spraying it. And it was still together.
