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In the realm of automotive engineering, the 4-stroke engine has long been a staple. However, despite its widespread adoption, it does possess some inherent limitations. Could you elaborate on three significant disadvantages of the 4-stroke engine? Are there any efficiency concerns, such as the potential for energy loss during the intake and exhaust strokes? Does its complexity lead to higher maintenance costs compared to alternative designs? And lastly, considering the rise of environmentally-conscious technologies, does the 4-stroke engine's emission profile pose a challenge in meeting modern emission standards? I'm keen to understand the nuances and challenges associated with this venerable engine design.