How to associate SLA dynamically to a case without using entitlement

Hi ,

I have 3 three SLA , one is associated with one custom service calendar with 24 hour support , another is  custom service calendar with 8 hours working hour and holidays , another without service calendar. All set as default to No..I want to associate dynamically SLA based on case type. If I am updating SLAInvolkId then SLAKPIInstance is not creating. Please suggest the solution how i will set the SLA dynamically to a case and SLA KPI instance need to populate based on SLA config.