One way to create a heavy launch vehicle is by clustering large numbers of small engines together in a stage. An example of this approach is the SpaceX Falcon 9:
Now I've heard people arguing against this approach, saying that the engines may interfere with each other and that you're better off using fewer, large engines. This argument often refers to the N-1 which used 30 engines on the first stage:
Now I realize that when you get more engines, you get more parts and as a result, more possible problems. But does the engine arrangement itself pose a problem when you have more than a few in close proximity?