Umm help?
 

Well I charged to my battery to 8.4v as normal then ran a 6 minute race and charger says over volt so I checked the volt it was 9v each cell perfectly 4.50v it normally comes back with 8v, how did the voltage go up? The battery is not damaged as far as I can see but it did feel a bit soft on acceleration but I did change rotor so I presume it was that

Dude, that is seriously freaky.
I think you could use technology like that to make millions with electric cars. I mean, you have broken the laws of physics! Congratulations :)

Perhaps though your charger has crapped it. Did you check the voltages using your charger to get those readings?

If you're using a DVM to check voltage, check the internal batt in the DVM - DVM with a low batt will read wrong and it will be higher than it should be.

It passed tech inspection they limit it to 8.42v........I used 4 different multimeters to check voltage

There is no way for the voltage to go up on its own especially after discharging it in a 6min race. There has to be another explanation.....

Yer, I know any possible answers?

Only thing that makes no sense - usually when something like this happens, a connection to a solder tab has come loose, but you're seeing half voltage in each cell which implies that's not happening. If both individual cells are still intact, then something is going on in the media which is prob not good, raising voltage and lowering amp production. I haven't heard of a lipo dieing with these symptoms. This might be unsafe....

That said, have you tried to discharging to see if voltage will come down so your charger will accept it? Watch for any signs that cells are starting to puff.