Thanks,
The one I have is 42 ID at rear and has a 47mm overall length, since rebuilding my JJ1400 and getting all my injectors working well I have been using the original two piece tailcone, as it had more than enough powere for my Bobcat.

Having to replace my wren 54 with my JJ1400 (bit ironic) after the wren blew up in my Boomerang (funny always thought it was the JetJoes that blew up) I wanted to get the most thrust I could as the boomerang is much heavier than the bobcat.

I have flown it about 10 times now with the two piece tail cone but it needs a bit more thrust so I fitted the single piece tail cone and the EGT's went very high 740-760 I had one flight and did had bags of extra power, but when I downloaded the fadec parameters the EGT's had been up at 785c so I swapped the tail cones back again.

I think now with the fully working needles the single piece cone is two small dia at the outlet and going to machine it down on the lathe (to make outlet dia larger) till I get EGT's about 680-700.
What is interesting is a friend sent his wren 54 back for repair and now it runs in the high 700's and the ECU was re set to 840max? I always thought 800c was a figure set more to protect the bearings and metals as most turbines seem to have a max of 800c