If you use a starter and a 6.5 gallon carboy then use a blow off tube also. About 8 hours after pitching my starter into some hefe wort this weekend the airlock was going faster than any of my previous beers with about 3 inches of krausen. Somewhere around 12 hours it blew through the airlock, there was just not enough head space.
May happen without a starter also, but probably more likely with.
Well, I didn't have time to make a starter...I haven't been able to brew much lately and had an free night this past weekend (which is rare!). I did rig a blow-off...48 hours into the primary and theres about 3-4 inches of krausen but hasn't gotten into the blowoff (6.5 gal carboy). The only thing is that I did a full boil and late extract addition...the boil didn't evaporate as much as I thought (started with a tad over 6 gals) and I missed my OG because of it (supposed to be 1.050, came in at 1.042)...I'm sure it'll still be ok though, just a tad lighter body...
On another note I bottled my first batch ever that same night, before I brewed the Hefe...roughly 6:30-7 pm until 3 am...man that was a long night!
For my Hefe I used White Labs WLP300 without a starter (though I did let it reach room temp over 5 hours). Within 24hrs I had the krausen blowing off into the tube at a crazy rate for 2 days(6.5gal primary carboy). Attenuation was great and after 1 week I transfered to secondary with only 2points to go on my expected FG.
My fermentation temperature was around 68-72 the entire time, and it has great bananna aroma and flavour.