You can get to the point where not all the gasses are forced out though, that is where porting, bigger exhaust housings, and longer duration cams come into play to allow you to get more from the engine, but as you say Rob it's not what this thread is about.

I'm just wondering with the above spec if the ports are stifling the engine a little, and if the gasses could escape quicker if the ports where bigger..... it could of course be that the inlet ports that are restricting on the way in and that the exhaust ports still have plenty of headroom?!

I dont know...