I have tried to use the modded sapphire trixx to allow undervolting beyond 100mV but when it is loading the GPU stays at idle and miner only shows 8MH/s so I wonder what could I do to undervolt the car dbeyond 100mV without modding the bios?
You could try in claymore miner's config.txt using the -cvddc switch. Usage is in the readme text file in the miner's folder.