I've had my JJ1400 for a little while now and it has been starting and running really well, I've posted a couple of videos of it starting and running in a previous JJ thread.
Last Sunday I changed to the single piece tail cone and ran the engine for about 4 cycles, the noise is a lot louder than with the two piece tail cone and you can actually feel it in your chest when it is flat out
I had a few problems with it though on the last couple of runs, it seemed to vibrate a bit more and I could see the bendix unwind and touch the spinner very slightly a few times. It also flamed out a couple of times when going from high speed to idle, the error message on the data terminal was "speedlow" even though it was running at idle (50000 RPM) I think (as I was not looking at data terminal at the time). on the last flame out after it had cooled down I checked to see if there were any obvious signs of either the compressor or turbine wheel rubbing, there was not but I did find that the bearing(s) had become stiff as the rotating parts would slow down very quickly when spun by fingers! Total running time so far 56 minutes and 6 cycles.
To investigate the matter I've taken the engine apart to examine if the bearings are the culprit and here are the pictures. By the way the other thing I noticed when using the single piece tail cone is the difference in the PWM needed to drive the pump. 160000 rpm; two piece pwm 400; single piece 280.