According to Official Guinness Records,
The fastest speed in a hearse is 186.04 km/h (115.60 mph) and was achieved by Shane Hammond (Australia) on the TDRA Dragway in Tasmania, Australia, on 20 February 2010. Shane undertook four runs, and covered a quarter mile in an average of 12.206 seconds.
For a complete list of 2010 records, please visit 2010 Guinness Records in Australia.