The E61 group design was created by Faema in 1961. Since then it has become a golden standard. The design is still very modern. Many high-end semi-automatic machines are using it still. Manufacturing capabilities have improved, gasket material, finish, and electronics are much better, but the design is still the same.
Just to understand the workings of E61 group head great guys on the web created a few drawings showing interal design.
…and even a thermal model of the E61 group head.
