Have you increased the front bar? If not I'd leave the rear alone. If the rear bar is too stiff you will find the car will oversteer at the limit, which you do not want on the street. The rear suspension on an SEC is significantly different than an ordinary sedan and the SEC is a pretty nimble car for its size which is more like a 124 in size compared to a 126.

If you want to stiffen it back there I suggest investing in a set of Koni adjustable shocks.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.