Measuring PP port timing

[sen2two]

I am checking my PP timing so I can scribe lines for additional port shaping and i am unsure where to mark for open and close on the port.

Does the port open when the apex seal moves past the bottem edge of the port?

Does it close when the seal after that passes the upper edge of the port?

Or is it when a specific porting of the rotor face passes the port?


Heres a picture of my ghetto set up. This is just a test set up. I am going to make a real set up later on. I just need to know if I am doing it wrong...

The mark on the rotor housing (0-) is TDC (Directly between the 2 spark plug holes). The degree wheel (I printed out one from online) and taped to a rear counterweight. The pointer is taped to the rotor housing and is stationary.

[RICE RACING]

Apex seal leading edge for opening (bottom extremity of the port, typically flat edge or bevel if it got a big one on it) & apex seal trailing edge for closing (on the outer apex *most are rounded* or tapered end to end at the middle of the port of the closing edge or bevel if its got a large one on it), obviously on the one chamber

So round port, flat open round close or square port flat bottom flat top or tapered it does not matter, you just pick the extreme ends and that defines your opening timing and closing timing on peripheral ports port volume to timing relationship is LARGE so a fraction of a degree either way due to a large bevel (rounded edges to the rotor housing surface is not that critical) just keep both the same. A flash light (pen light) helps you pick this rather than naked eye.