Wow!! There is a lot more here than I initially realized.

--Spike

 

OP im not gonna dick you out, i usually would have, but im back from vacation so i will say this.

What your feeling is the weight transfer of the car when you hit that uncomfortable feeling in the turn, its happened to me a lot so i know exactly what your talking about. Go take some HPDE classes, it will really help you learn the limits of the car. I learned how to time the transfer and it made a whole world of difference on the stock suspension, the car holds everytime i take turns hard, track or street. Ive turned 45mph turns into 85mph turns after instruction. And keep it on the track man, we have fun with our Zs but we do it in controlled environments. Sure we all drive spiritedly on the streets, but we arent going so fast and hard where we could possibly kill someone or something. Last thing get some better tires, they will help with the cornering, I use hankook v12s, everyone has their favorite though