Originally Posted by YmeBP

My suggestion and experience is that if you can handle 8.4 you can handle 9.9 provided that you don't lock up the drive train and hammer the throttle. I've seen speedo's rated for 4s fry on 2s when someone tries to bring a broken car into the pits and keeps hammering the throttle and smokes the speedo.

So ... on to the specifics, could you post what brnad and model your speedo is. That will help us figure out how many amps/volts your speedo can handle which would make it easier to give you a definitive answer.