BOINC is a platform for volunteer computing. The server component of BOINC embodies a number of scheduling policies and parameters that have a large impact on the projects throughput and other performance metrics. We have developed a system, EmBOINC, for studying these policies and parameters. EmBOINC uses a hybrid approach: it simulates a population of volunteered clients (including heterogeneity, churn, availability, reliability) and it emulates the server component; that is, it uses the actual server software and its associated database. This paper describes the design of EmBOINC and validates its results based on trace data from an existing BOINC project.