I was just wondering why is it that PP have to be high rev only engines with no low down tourque? Wouldn't this be more a function of port size, could you make a PP with port size similar to a stock port (Not that you would want to in reality, but this is just hyperthetical)?

 

I suggest you read about rotary engines. For your information the first production rotary engine was a PP, the NSU engine in their Prinz spyder, while both Citroen rotaries were PP, the Ami 6 and the Birotor.

 

Yeah, I know that, I also thought that our exausts ports are PP. That is why I was wondering why when people talk about PP they talk about engines with the charictoristics above? Apart from emmisions what advatages/disadvantages are there of PP vs. side ports?

 

There is over 150 degrees of overlap with a peripheral port intake and exhaust. That much overlap allows exhaust to get sucked into the intake charge, causing exhaust gas dilution. Very bad at low rpms, reducing power. EGD has less impact at high rpms when the motor is spinnig so fast.

Also the big port size reduces velocity and therefore low end torque.