Antminer V9 custom firmware is not available Meanwhile you this check this guide to overclock your Antminer V9. Furthermore, you can check for any firmware upgrade at Bitmain.
About Antminer V9
Antminer V9 can give a maximum hash rate of 4Gh/s for the power usage of 1200W. The miner is currently not profitable for mining Bitcoin but there are other more profitable SHA-256 algorithm coins. It uses a BM 1580 ASIC Miner chip for improving the mining performance.
Custom Firmware for Antminer
We have successfully tested a custom firmware on Antminer S9 and T9. It enabled more frequency options for overclocking and will enable full control over the miner. You can adjust the fan speed earlier which was not possible. This Custom Firmware can be used to low the power usage. Furthermore, it is very beneficial to use custom firmware.
Recommended - Is it safe to overclock Antminer