The following article describes the history of the fuel-engine interface in two case studies (from 1900 onwards) with the goal of understanding the complexity of such an interface composed of two technological systems that do not form a clear hierarchical relationship. A technological setting with two divergent cores is particularly prone to external influence, in particular to governmental regulation. The proposed framework in this article complements and extends the existing literature on technological community in particular regarding: (a) the importance of the interface between industries that are not subordinate to one another, (b) the role of the regulator, and (c) the focus on hidden uncertainties. This study illustrates how certain types of uncertainties within complex innovative projects can result in inertia and sub-optimal solutions. The proposed framework has implications for theory, management, and policy practice. © 2005 Elsevier B.V. All rights reserved.