All the .247's where 6-port. The only real difference between the pro and and standard version was the carburetor, and the pro had brass bushings on each end of the rod. The older standard version had a small cooling head, but they made the larger head standard on all versions shortly after it introduction, unless you bought an X-factor. And yeah, I've owned both, and actually took a piston/sleeve from a pro version and put into a friend's standard engine. And to be honest, you couldn't tell the difference between the two engines before or after the piston/sleeve swap. I ran the standard version for a while, and it felt just like my pro version. They are strong, robust engines no matter how you slice it. I think that RC-car magazine said once, "the .247 is the most trouble free engine, period."