my brother-in-law has a 09 Charger R/T, says the computer shuts the fun off at 138mph.

 

According to the specifications on my 2008 SRT8 Challenger the top speed is electronically limited at 170 mph.
I will never have to worry about it, as I can't see myself ever trying to hit those kinds of speeds............(But, it looks good on my car show info display)

 

The Challenger made its fateful return to Dodge’s lineup in 2008 following decades of remaining dormant. For the 2015 model year.