I think the issue was that the front/rear braking bias got messed up. and the rears were doing more than they should (relative to the fronts) which made the rear end try to jump out if not braking in a perfectly straight line. He spun out on track a few times. It was nearly 4 years ago, so I may not have all the details correct.
I am also running stock powertrain in my Contour. All my track relevant upgrades have been suspension, braking, and subframe connectors. If you're still using only the OEM 3 point seat belt, I recommend getting the CG Lock device. It keeps the lap portion of your seat belt tight, holding you in the seat better, without restricting your movements from the upper portion of the belt. I started using it last year and I noticed a big difference at the 3 events I did in 2017. Check it out here...
http://www.hrpworld.com/store/defau...ock-performance-add-on-for-your-seatbelt.html