[rx4ur7]

Length for timing, width for volumn.

If you want it to be somewhat drivable then not PP. Great if you just want something that makes a lot of noise and goes bloody fast and really doesn’t work well at low speed then go for it. PP is best for all out racing.

As to port size, larger is not necessarily better. Ask Paul Yaw. He is one of the few if the only one that has used a flow bench to figure out porting. In the old days we would just make the holes as big as possible thinking that was the way to go.
There is a lot to be found in the earlier motors, 15/20%, pre 93. (84 to 91 13B not so much, six port he found you really had a hard time making them flow as well as the four port)

93 on Mazda has made a lot of improvements in flow characteristics. When Paul was in Tucson I was able to use his flow bench to develop the ports and intake for my FD package. It was the first time he had seen an FD housing on the bench. He saw the readings and wondered what porting I had done, he was impressed. It was a stock housing that I was using to get the base line. The stock FD housings flowed as well as ported early housings. I was able to get the steel plates to flow 98% and rotor housings 100%. Was also able to improve the flow in the FD intake which actually flowed better stock than early modified manifolds. Could only find 8 to 9 % though. But as he found out the increase in flow in the intake usually equated to same % increase in hp.