So whats the difference between a chipped P28 and a chipped P30? I was reading somewhere that the P30 can use the stock O2 sensor to run closed loop so that the car will aim for 14.7 air/fuel ratio all the time. And this is benefit is really for the purpose of an emission test. Is this the only difference?

 

There is no difference besides the knock board. (the p28 does not use a knock sensor which is useless anyhow).

Both ecus have narrow band o2 feedback capabilities.