Alloy 718, developed and patented by International Nickel Company in the 1950’s is utilized in jet engine structural applications in a number of product forms, including wrought, powder and investment castings. Alloy 718 is preferred due to its good balance of elevated temperature properties and manufacturing flexibility. A large percentage of jet engine structural components are fabricated using investment castings; castings may provide a lower-cost material alternative to complex built-up structures. There has been a significant volume of work in the metals-producing industry to increase the temperature capability of Alloy 718. Allvac* 718Plus* was developed as a cast-wrought material as a lower-cost alternative with elevated temperature mechanical properties roughly equivalent to those for alloys such as Waspaloy and Rene 41. Allvac 718Plus provides these property enhancements, with manufacturing characteristics such as formability and weldability that are very comparable to Alloy 718. Weldability is a particularly important manufacturing consideration with investment castings as they are commonly weld-repaired during processing. The microstructure of Alloy 718 in the cast condition tends to be highly segregated, due to preferential partitioning of Nb to interdendritic regions. Additionally, since Nb has a relatively low diffusivity in a nickel matrix, the extent of segregation cannot easily be reduced through homogenization. Utilizing Allvac 718Plus as an investment casting requires a thorough understanding of the homogenization and heat treatment response of the cast microstructure. The objective of this work is to develop an optimized heat treatment practice and preliminary mechanical property data for Allvac 718Plus investment castings. Cast-to-size test bar molds were manufactured and evaluated for porosity and microstructure homogeneity. Samples were subjected to a heat treatment study to understand the response to various solution heat treatment and aging conditions. For each condition, a set of mechanical properties was generated, and the data compared to relevant investment casting specification minimum values. From these data, an optimum heat treatment practice was developed for Allvac 718Plus investment castings. *Both Allvac and 718Plus are registered trademarks of ATI Properties, Inc.