Hi Rob i am using a Wren pipe with my F16, it is much lighter and saves a lot of nose weight,a gap of 30mm between engine and pipe is fine and you will find that thrust loss is at a minium,mine fly,s well on a super sport and in the next RCJI i have writtern a review.The single wall pipe doe,s not get that Hot and gases that exit the pipe are around 200c,i have wrapped ceramic paper around pipe,just where the tail servos are just to be safe,and covered servo leads with sticky ali foil,regards Keith W