[marks crf]

well the pressure was pretty bad with mine it popped off the plug that i put in the end that connects to the muffler and there was about a 10cm ice stake comming out

luckly it blew the plug or the damage could have been worse.......................but the split is fixed now rewelded it.

[motosicko]

I had an FMF Gnarly pipe on a YZ250 that I got a huge dent in it in a race at Lake Whitney Amateur National. Luckily FMF had a support semi at the race and they plugged each end and one plug had a air fitting on the end and they heated the dent and used compressed air to perfectly remove dent. I'm thinking the freezer method is too much for the larger expansion chamber to handle. More water volume=more expanding as it turns to ice. On a 4 stroke header pipe it expands just enough to not split it open.

[wexy21]

True....but water/freezing method is much easier and requires no tools. So for most people, who don't have any way to get to a setup like that, it's the only way. But two-stroke pipes (well the ones that I've done) have always split on or near the seems, so for a small header I would imagine that it wouldn't split even if you over fill. It should just pop frozen water out one of the caps. There is also no huge void to fill like in the expansion chamber, it's all even. So as long as you use a plastic cap, which is the weakest part of the setup you should be fine. But those are just my thoughts on this.