The two are easily distinguibile in pronunciation. (Context could help if a speaker does not enunciate clearly.)
tried to has a distinct d sound not heard in try to. And yes, the vowel length is probably longer in the latter.
For instance, I try to brush my teeth and I tried to brush my teeth are easily distinguished by listening.
I can't find two sentences that are the same except for try to/tried to, but the following may help:
try to -> http://forvo.com/phrase/i_might_try_to_explain/
tried to -> http://forvo.com/phrase/she_tried_to_reach_the_vase_but_overbalanced_and_fell_off_the_stool./
Note the speakers above speak at s different rate, so it's not s perfect comparison, but it should illustrate the difference. Of course, the ending t in might is not pronounced fully before the beginning t of try to, unless the speaker is deliberately speaking slowly and stressing each word.