The P-42, was striped of literaly everything that was not needed to fly the thing and (barely) to maintain the pilot alive, the entire avionics suite, including the radar, the mission computers, every single piece of operational kit, the fins, the tailboom, the wing tip launch rails were removed, the paint was taken out, it received a new (lighter) radome, on top of that the two engines were twiked to produce another ton of thrust each. The aircraft was so light that the thrust-to-weight ratio was almost 2:1, this means that the clean weight of the P-42 would be on “Mig-29land”.
http://www.angelfire.com/ab4/airplanes/Sukhoi/Record_Flanker/P42.html
The P-42 was has removed from an operational Flanker that Sukhoi could manage, and still be able to fly.
Be careful that all the records have not been realized by the “all striped” P-42 (mainly time-to-height speed) but also by a Su-27P (more lightly striped and mainly for speed in close circuit)