Woah, that will make an engine of 301.584cc !!!

I want to make, in the distant future, a 4 or 6 cylinder inline engine of about 400cc-500cc capacity. Nothing flash; probably a pushrod operated, 2 valve per cylinder engine with dry sump and water cooling. I like to make engines which I can actually use for something, rather than just display models (though I enjoy the display ones as well, just not as much)

Why such a large bore to stroke ratio?