It's not your carrier. SMA is a protocol. It specifies a data length of 140 octets which in the Latin alphabet (the one used in English) is 160 characters. If your app limits you to 80 characters use a different SMS app. (Anything more than 160 characters is sent as multiple SMS messages [which the app reassembles into one "message"] or as an MMS text file. Some apps do one, some do the other and some let you choose whether to break the message up [send it as multiple SMS messages] or not [send it as an MMS]).
There's no way to change SMS to allow a single SMS message with more than 160 characters, that's part of SMS. It's like making water dry. It might be dry but it wouldn't be water any more. (For instance you can send a 2,000 character message, but that's called email, not SMS.)