While scaling law results on the performance of mobile ad hoc networks (MANETs) have been extensively reported in literature, the exact performance of such networks, particularly their real achievable performance under practical network constraints, is still largely unexplored. As one step toward practical performance study for MANETs, this paper considers a MANET with constraints on both buffer size and packet lifetime and explores the impacts of such constraints on network performance. Analysis on the exact throughput capacity of the network is first provided to reveal its maximum possible and input rate-independent throughput performance. With the help of the embedded Markov chain theory, a complete theoretical framework is then developed, which enables the achievable and input rate-dependent throughput and packet loss ratio to be derived in closed form under any exogenous rate. Based on the M/G/1/K queueing theory, the packet end-to-end delay under any exogenous rate is further studied to give a relatively whole picture on how buffer size and packet lifetime impact the network throughput, packet loss ratio, and packet delay.