I think the stock Yaris has enough power

[regal]

Originally Posted by cali yaris

I *think* you mean understeer, not oversteer. It's difficult (but not impossible) to give a Yaris oversteer handling. Easier to make it neutral (my preference), and we all know (I think) it's designed to have understeer (= go straight when you want to be turning), which is safer for novice and untrained drivers.

increase oversteer/minimize understeer

stiffen the rear (springs, braces, sway bar, etc)
raise the rear tire pressure
soften the front
lower the front tire pressure
... and more...

Your right I meant understeer, seems there should be some rear bracing that would help I tried all the above.