Here's a HP calculator that use ET and MPH, the MPH is the more accurate of the two and has been used for years, maybe since 1/4 mile drag racing started. Be sure to use scale weight as raced (with driver and equipment and fuel load), shipping weight or manufacturer's stated or title weight are not accurate, and will give false numbers. Shows my '73 that runs high 11's with a little over 410 hp to the wheels.
opps, forgot the link;
http://www.wallaceracing.com/hpcalculatorquarter.php