Great youtube channel.

One of his videos is him working on a tractor year or two ago.

About 30 minutes into the video. he discovers there are holes in exhaust manifold which is causing tractor to not start.

I am curious as to why that is. Isn’t the exhaust pipe a long ass pipe through which air can get in and get sucked into the engine and cause same issue as exhaust manifolds having few holes?

I am not super familiar with the exhaust side of things. Explain if you know.