Shrinking cycle time with concurrent engineering can make projects more difficult to manage. However, the extent, nature and conditions of the causal relationship between concurrence and manageability are not well understood. This study uses Degree of Concurrence and Degree of Concurrence Relationship Curvature as two measurements of dynamic concurrence based on Process Concurrence Relationship, an improved tool for describing and modeling concurrence, and uses the standard deviation of Process Work Queue Acceleration as Manageability Index to model project manageability. Single-phase development process model is applied as a data collection tool to investigate the causal relationship between concurrence and manageability. Two hypotheses were developed to test the causal relationship separately with the two different experiments - Linear and Nonlinear. The study finds a significant inverse relationship between degree of concurrence and project manageability with linear concurrence relationship. When the concurrence relationship was changed from linear to nonlinear the relationship became quite unexpected. The results improve the understanding of the causal relationship between dynamic concurrence and manageability.