Does anybody know what the top speed of an 06 Impala SS with the 5.3 V-8 is? I know it would be a computer limited speed, but would be interested in knowing just where the limiter would kick in. I think the 18" tires are good for about 156 MPH but I'm pretty sure the car would probably not run that fast. I had mine out on a dry, flat section of 4 lane with absouletly no other cars around and punched it out once and it jumped up to 120 MPH pretty fast and I chickened out at that point and let off of it. It was still pulling pretty hard at 120 MPH and I wondered how much more it had before the computer stopped the acceleration. The car is definately strong, I had a '64 and '65 Impala SS and both were pretty strong, but they would not hold up to these new Impala SS.
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I can't tell you what the computer limited speed is because, same as you, I am chicken. But I can pass along what I read. The ungoverned speed according to Car and Driver is 154mph. Read the article:

http://www.caranddriver.com/roadtests/11028/road-test-review-2006-chevrolet-impala-ss.html

Actually, the "W" rating of the stock tires are good for more than 156mph. It is good for 168mph.

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=35

I have a 2003 3.4L Impala and the speed limitter setting in the PCM is set , or was set, at 126mph. I set it to 140 ( wishfull thinking ) . Just remeber too if you get caught doing those speeds you are more than likely will be arrested. I would go to NAIOA's forum they can tell you for sure.