We have tried timing boats manually and this will be the same case. If your timers both at the entrance and exit are each .25 sec off and you make a 6.5 sec pass then you just went 94mph. That's almost 8mph difference with a human having reaction time of .25 sec. I have not seen anybody yet with that reaction time so your numbers could be outstanding or not worth mentioning. It is a difficult task. If you know a cop or somebody that does, see if they can get him with a radar gun at the field. They usually get a kick out of it.