I just don't think it can flow properly and make the power... irrespective of length etc, I've never found anything less that 3.0mm to be efficient, and generally unless the port is exceptionally long (like an LGV), 3.2 is a more usual minimum starting point.

Even 25mm cylinder guns with fairly heavy pistons found 3.0mm too tight, and had to open out to 3.2. And larger bores 26/28/30 3.2 is always too small.

Discuss.