The present paper is part of a wider project examining vowel compression and its impact on the phonetic signalling of stress across dialects of Spanish. Here within, we compare vowel compression effects in spontaneous Southern Chilean Spanish to previous findings from continuously read Altiplateau Mexican Spanish. Results show that, in Southern Chilean Spanish, vowels are shortened in CVC and CCV syllables irrespective of stress; although unstressed vowels are shorter than stressed, onset and coda-driven compression effects are visible on all vowels. Qualitative results show that stress-driven differences in vowel height are visible on /o/ and /a/ in open but not closed syllables: stressed vowels are lower in the vowel space. Conversely, results from Altiplateau Mexican Spanish showed that whilst unstressed vowels in CVC syllables were shortened and centralised, stressed vowels were not. Results therefore support theories that dialect-specific compression effects exist due to dialect-specific phonetic-phonological interactions (Authors under review): in this case, their interaction with stress. We further consider the implications of these variety-specific patterns in the context of debates concerning the dialect-specific nature of stress, arguing that compression effects may have implications on the wider vowel systems and the phonetic way in which stress is signalled across dialects.