Tomas: The easy answer is "it depends".
It depends on what temperature the clay was meant to be fired to.
It depends on whether you mean Celsius or Farenheit. (May I assume Celsius?)
It depends on whether or not it will be exposed to direct flame. (I assume not)
It depends on what purpose you have in getting it to that temperature, and what the clay will have to hold while doing so.
You need to give much more information in order for anyone to be able to give you a definitive answer.
If you are looking for a formula for a "make it yourself" clay body, the answer is "NO".
For those kinds of temperatures, you need a silicon carbide type material, something you cannot do at home.
Hope that helps,