Originally Posted by MeltingAlf

T1, T2 and T3 are connected airside so you can walk from T2 to T3 (via T1) if you have the time. There are Skytrains between those three terminals both airside and landside so that's not an issue. Security in these three terminals are also done at the gate so arriving and departing passengers are mixed.

T4 is connected via buses and again, has airside and landside ones, and has a different set-up to T1-3.



Two hours is more than plenty of time at SIN.



Your worst case scenario at SIN is going to one of the transfer desks to print a boarding pass. That is, if you're on a full-service carrier and not on one of those budget ones. If you're on AirAsia or VietJet chances are you'll have to clear immigration for that.

But then again, does it make a difference? T1-3 security at SIN is done at gate. Immigration at SIN is almost all automated now. It's possible to clear immigration, get your boarding pass at one of the self-service counters, and be back in airside in the matter of 10 minutes.
I've made it in under 15 minutes from getting my Grab at where I lived to being airside at SIN. This includes clearing immigration and getting my boarding pass printed with the self-service counters.