I had changed my exhaust to Vance and hines short shot recently.
When i start the bike in the morning, idle roars , but slowly the idle comes to normal sound.
How can i get my bike's idle to sound in a same way. Probably because of engine not hot enough. Or i dont know. Please help. TIA

 

You answered your own question, the engine isn't hot enough. It is running at a higher idle due to it being cold. If you have a tuner which would allow you to adjust the idle, you could lower it. The down side is it could want to stumble and stall with to low of an idle for the cold engine.