Does a flat-6 engine any different from an inline-6 or V6?
Yes. A flat-6, such as found in Porsches and Subaru’s has 3 cylinders on each side and they are located 180 degrees from each other. That is, they are “flat.” Some call them “boxer” engines. An inline-6, such as found in BMW’s and 1960 Plymouth’s, has all six cylinders straight in line with all the other cylinders. A V-6 has 3 on one side and 3 on the other, but they form an angle instead of lying flat as in a flat-6. Most American and Japanese cars offer V-6 engines. The angle might be 60 degrees in some cars and more or less than that in others.