Stop-light racing is severely limited by traction in a Cobra. Therefore, to improve your "time to XX (fill in your number) MPH from a stop", you can do a few things ...
1) Practice ... what RPM to come out of the hole. I've seen stock VW's beat muscle cars for the first 30 feet
2) Play with rear tire pressure
3) Get rid off your tires and add a set of sticky tires
4) Change rear gear ratio to higher number
5) New mufflers - OEM's are really restrictive
As far as the nitrous is concerned, it should be activated as soon as the tires stop spinning ... without spinning the tire more ...
When yer layin rubber, HP is irrelevant. Put a blower fed by dual turbos ... so what ... ya ain't going to go any faster til the tires stop spinning.