What`s the rest of your combo? you should always cam in accordance to the rest of the engine. However, a small lumpy cam in a 350 will idle smooth in a 400, since the extra 50 cubic inches swallow it. Bigger make for higher rpm use, but other varibles play a role in this as well. If the engine is stock you can run up to a 224 duration @.050 cam, but make sure you match the valve springs.