With any rear sway bar install it is important to align the rear subframe, and then check the toe. Its too easy to end up with trust pushing the car to one side.

If the car has undrivable oversteer i would suspect the rear spring rate is progressive, or your hitting the bump stops. Or rear toe is extreme.

Re the stock bar, im going to run no rear bar, with 500lb springs, (400lb rear corner weight) this will keep the rear rate completely linear. And stiffer springs = less strut compression. So hopefully i can hold that 1.7g and still have compression left. Setup suggested by a national champ/builder.

Tune with springs. As mentioned earlier in this thread "rear sway bar is an inxpensive bolt on upgrade, that allows tunning without upgrading anything else."

 

after several great drivers told me to loose the rear bar for fwd.
Running 2 events with no rear bar has made the car reliable in corners.
I too had the h sport comp. On the softest setting i was getting progressive spring rate inscrease on the loaded wheel and snap spins when loading the suspension in transition after a sweeper.

Without the bar my spring rate is 375lb/in but my rear corners are only ~400lbs. My front rate is 500 with around 700 lbs per corner. So the car oversteers nicely and consistently.

Im running 1/32 toe in on each rear wheel. Rear Ride height is 1/2 below stock.

The front bar is stock with spherical links.

If your car is stiff in the rear, remember you have to stay in the throttle when the back end gets loose or you will spin

At highway speeds the lack of a rear bar is a little unsettling.
But i only am driving to events.