1 hour 40 minutes should be ample, especially as you can walk/run from the Ryanair arrival terminal to Border Control. Even allowing for a 30 minute wait to clear Border Control and another 30 minutes to pass through security you will still have half an hour to spare.
BUT, as has been mentioned before, if your inbound flight is late, you have had it!
Last edited by wowzz; 5th Apr 2012 at 20:16.