This is getting off topic, but since you asked....
The Pratts seemed more sensitive to rapid throttle movements until they implemented the super duper electronic fuel control systems. The GE motors were lots less sensitive, and you could slam the throttle to max or idle with no problems.
The TF-41, aka Spey, was great about rapid throttle movement, but it took awhile to respond. So in formation you pushed up/pulled back and then resumed the original throttle setting once you saw movement. The F100 in the Viper was much quicker on the response.
One characteristic about the Pratts was they did not like going to burner under a gee load. Saw it with the J57 and then the F100 years later.
But back to the main topic, huh?
I still wonder about an annular duct as we had on the fans I flew. Maybe some intake or bleed doors, but use all that fresh air back in the burner.