Do you need a vehicle speed sensor

Doing a ls1 retro fit and runnig a turbo 400 box, do i need to run a vehicle speed sensor

Need to, No. Works better with one, yes. If you have a mechanical speedo output on trans there are available add on sensors.

Ok thanks, do you know what parameters the computer would use the speed sensor for apart for gearbox control.

Idle and spark table selection.

cheers ill look into hooking up the adapter.