I had the great pleasure of flying a highly modified Chipmunk for a while. It had a 300hp Lycoming engine, a modified bubble canopy, standard hydraulic brakes on the rudder peddles and the vertical stabilizer and rudder size had been increased to handle the torque from the engine.
You could do a inside square loop with no problems, the guy that owned it would do outside square loops, I wasn't that brave, or that eager to pull that many negative Gs for so long either for that matter.
A very sad end to the story of my friend owning that Chipmunk. He got married, started having children and his wife made him sell it.
I never did find out what happened to it after he sold it.
I just remember how much fun it was to fly.