Hey torranceboy: You need to check out jpouch.org - so much information there, and numerous discussions regarding the exact issue you raise.
But ... you have a loop ileostomy now, which means it's higher up in the tract and therefore less water being absorbed (more liquidy output). When your jpouch is connected and you're using it, you will be working with more small intestine which translates to more liquid absorption (the jpouch will learn eventually to act more as a colon), and therefore, the output will NOT be the same as with a loop ileostomy. I went through this many years ago, and with the loop, I was scared to death that the jpouch would have a similar output. Happy to say that was not the case. Your output will NOT be as voluminous/watery when you're connected.
Best of luck with your takedown!