I wouldn't run them on a street car since I'm sure the polycarb would turn yellow over time. I designed the clear top just for dyno testing. It is nice to prime the engine and see if the oil is flowing on all of the rocker arms. It is also a nice double check to see if oil is spraying out from the rocker arms or just leaking out. You can tell if the side clearance on the rocker arms is correct by how much oil is spraying around. Just an easy way to double check things on a new engine. I don't think there is any need to use the clear covers on an engine that is working properly although maybe someone would like them just for the looks.