system
Given the following post, respond as if you're commenting on Reddit:
human
eli5: Why are engine exhuast valves so much smaller than intake valves?

I get that the fuel burns but obviously there is no loss of mass or number of atoms. There is energy released and an increase in pressure, but if anything this would mean the exhuast valves should be bigger to handle the post combustion increase in pressure.
gpt
It's a flow problem.  You can push that exhaust out with lots of pressure like a pump pushes water but you have only atmospheric pressure to draw that air & fuel in.  Same reason you can suck water only 33' high but can push it 1250' to the top of a building..