I had a Wren 54 TP in a Carden 35% Extra. It flew very well. The seperation of the cool intake air from any hot sources is very important. I made a mistake and overpropped the Wren 54 and did a lot of damage.(Overheating). Once i got the prop size right it was great. Wren had built in a great smoke system ( smoke pipes on both sides) and it produced super dense smpke. I used a Tamjets variable speed pump and Super Dri oil.
http://www.youtube.com/watch?v=bpemSYH59Mc
Over all I liked the Wren. Wren have stopped making the 54 size TP.
Regards