they retain the factory limiter. i read an article on a test they do every year in michigan i think it is, they tested the intrepid, the camaro, the hummer, the crown vic interceptor, and the impala. the hummer was the worst, 1/4 in 22.11 @ 61.8, and a top speed of 85 mph. the camaro was obviously the fastest, 14.14 1/4 and 159 top end.

police interceptor (vic) 0-60 9.14, 16.99 @ 84.1, 128 mph
impala, 9.25, 17.02 @ 83, 126 mph
intepid, 9.14, 16.98 @ 85, 136 mph
hummer, 20.65, 22.11 @ 61.8, 85 mph
camaro, (auto, 3.23) 5.69, 14.14 @ 102.48, 159