They made the impala's the same as the 9c1(cop cars). They got everything from 17 inch wheels to harder bushings, stiffer springs , oil cooler, heavy duty everything, fast ratio steering,etc. The old 9c1s even had reinforced frames, but i don't think they continued this to 96.
I strongly agree with Lloyd....they both have the same factory Corvette engine 350cu in........the LTZ is more of a Luxury Touring car, and the SS is the Super Sport version of the Impala.....if you remember way back, it started with the Impala, then the Biscayne was introduced, (a stripped down Impala) then finally the Caprice was added as the top of the line. The both come with factory duals, and sound about the same......but I believe the SS came with stainless steel exhaust though.... I sure miss those old big-block rear wheel drive cars! These newer midget sized cars they're building today, don't even have the right to wear the bow-tie badge. Even at that, the LTZ and SS at just under 4100 lbs., can still do the quarter @ 13.7.....at about 113. That's not too shabby for a big car.......0-60 in just under 6secs. with lots of torque for a small block!