I just got new pionner speakers which are 240w. I connected them to my pioneer head unit which is 50x4. If i blast them will i blow them out since each speaker is only getting 50w.
50 watts on your headunit is your MAX POWER. You're really getting about 22 watts per channel RMS continuous. If you crank your headunit, you begin to get distorted audio, which will eventually destroy your speakers because you're not getting enough power to them. Are your pioneers 240 max or RMS? I'm guessing your RMS is a lot lower.
Like Doo said, get an amp for them if you like it loud and you'll have less to worry about. You want clean power, not absolute power. Thats how you wreck your system.