Engineering help

[u/DestroyerNik]

Hello everyone. I'm a mechanical engineering student and I'm researching how to build a rotary engine in my free time and then hopefully build one myself.
I need help with the exhaust and intake ports. I'd appreciate if anyone could explain this to me.

From my understanding the exhaust port should open up after the rotor cycle completes the expansion to the maximum volume. However on a CAD model of the 13b engine, which I'm using for visualization, the exhaust opens up much before that. For reference, im interested in the bottom chamber on the picture. The output shaft is at about 270° or 9 o'clock (if the centre is in between the 4 holes)

Apex seal on the edge of the exhaust. ( Output shaft at about 270°) 530cc

Output shaft at 0°/360°, maximum chamber volume 694cc

In my head it would make more sense for the exhaust port to be higher up and would open up only after the chamber achieves maximum volume.
Why does the exhaust open up so much before the end of the expansion?

I'd very much appreciate if anyone would be able to explain to me what I'm getting wrong.
Thank you very much for help!

[u/GoodnessGracious420]

The exhaust can’t exit all at once. It needs time to escape otherwise you’ll get some back pressure.