225 slant 6

And why..? It seems unless you're on some kind of certain mission to make little do more or just happened to have all kinds of extra parts and time.. so for me it's always back to the burning question "and why" wouldn't you spend the same money and get more?..
you should see my old threads where I wanted to make my 318 the world's fastest. Unfortunately it was more expensive than doing it 360...
The reason being more parts are made for it so it's more common and less expensive. just been my experience trying to make something faster...