If the SRT did the 1st quarter mile in 11 flat, that leaves about 2 seconds for the second quarter mile stretch, in order to complete the 1/2 mile in the claimed 13 something seconds. (As someone stated earlier).
How fast would the Viper have to go to cover a quarter of a mile in 2 seconds?
If you consider that 1/4mile in 2 seconds is equivalent to 1 mile in 8 seconds, and since you know that 60 miles an hour is one mile in one minute, then you can divide 60 seconds by 8 seconds, which yields a factor of 7.5, then multiplying this by 60mph, means that the Viper would have to go 450 miles per hour to cover a quarter of a mile in 2 seconds.
(Sorry thats a little rough to follow, but it works out. Try it.)
You can work it backwards, by dividing 450 mph by 60, which yields 7.5 miles per minute. Dividing 7.5 m/min by 60 yields 0.125 miles per second, so two seconds gets you 0.25 miles, or a quarter of a mile.
edit Isn't this fun?