This acoustic study investigates voiceless stops in Guaraní that are described as transparent to nasal harmony. Voiceless stops in oral versus nasal contexts are examined in relation to theoretical issues of locality and phonetic implementation. First, the oral/nasal and voicing properties of the stops are considered in connection to proposals in phonological theory that feature spreading produces strictly continuous spans of a spreading property. The stops are discovered to display the acoustic attributes of voiceless oral obstruents; no evidence of nasal airflow energy was observed during closure nor was the closure fully voiced. These results suggest that strict continuity of a spreading featural property is not always found in the phonetic output. Second, the timing of the voicelessness is addressed. Interestingly, the duration of voicelessness of the stops [p, t] remains the same across oral/nasal environments, although the voiceless interval shifts to persevere longer into the following vowel in nasal contexts. The velar stop does not exhibit an increased perseverance of voicelessness after closure release—it displays the longest VOT of all places of articulation, and its VOT remains unaffected by oral/nasal context. It is suggested that incorporating a notion of conflicting realizational requirements in models of phonetic implementation is important in interpreting these results.