The delta wing, while excellent for a fast-climbing interceptor, meant any form of turning combat led to a rapid loss of speed. However, the light loading of the aircraft could mean that a climb rate of 235 m/s (46,250 ft/min) was possible with a combat-loaded MiG-21bis, not far short of the performance of the later F-16A. MiG-21's Tumansky R-25 jet engine's specialty was the addition of a second fuel pump in the afterburning stage. Activating the ЧР (rus. "чрезвычайный режим" - emergency mode)(Emergency Power Rating, EPR in India) booster feature allows the engine to develop 97.4 kilonewtons (21,896 lbf) of thrust under 2,000 meters (6,600 ft) of altitude. The rpm of the engine would increase by 2.5% and the compression ratio would thus increase, with a rise in exhaust temperature. The limit of operation is 2 minutes for both practice and actual wartime use, as further use causes the engine to overheat. The fuel consumption increased by 50% over the rate in full afterburner. Use of this temporary power gave the MiG-21bis slightly better than 1:1 thrust-to-weight ratio and a climbing rate of 254 meters/second, equalling the F-16's nominal capabilities in a close-quarters dogfight. The use of WEP thrust was limited to 2 minutes to reduce stress on the engines' 750 (250+250+250) flight hours lifetime since every second of super-afterburner counted as several minutes of regular power run due to extreme thermal stress. With WEP on, the MiG-21bis's R-25 engine produced a huge 10–12 meter long blowtorch exhaust, with six or seven brightly glowing rhomboid "shock diamonds" visible inside the exhaust. The Russians gave the emergency power setting its "diamond regime" name, never used in India. Given a skilled pilot and capable missiles, it could give a good account of itself against contemporary fighters. Its G-limits were increased from +7Gs in initial variants to +8.5Gs in the latest variants.Král, Martin. "MiG-21BIS." Soviet Hammer, 6 April 2012. Retrieved: 28 June 2012. It was replaced by the newer variable-geometry MiG-23 and MiG-27 for ground support duties. However, not until the MiG-29 would the Soviet Union ultimately replace the MiG-21 as a maneuvering dogfighter to counter new American air superiority types.
The delta wing while excellent for a fast-climbing interceptor meant any form of turning combat led to a rapid loss of speed However the light loading of the aircraft could mean that a climb rate of 235 m/s (46250 ft/min) was possible with a combat-loaded MiG-21bis not far short of the performance of the later F-16A MiG-21's Tumansky R-25 jet engine's specialty was the addition of a second fuel pump in the afterburning stage Activating the ЧР (rus "чрезвычайный режим" - emergency mode)(Emergency Power Rating EPR in India) booster feature allows the engine to develop 974 kilonewtons (21896 lbf) of thrust under 2000 meters (6600 ft) of altitude The rpm of the engine would increase by 25% and the compression ratio would thus increase with a rise in exhaust temperature The limit of operation is 2 minutes for both practice and actual wartime use as further use causes the engine to overheat The fuel consumption increased by 50% over the rate in full afterburner Use of this temporary power gave the MiG-21bis slightly better than 11 thrust-to-weight ratio and a climbing rate of 254 meters/second equalling the F-16's nominal capabilities in a close-quarters dogfight The use of WEP thrust was limited to 2 minutes to reduce stress on the engines' 750 (250+250+250) flight hours lifetime since every second of super-afterburner counted as several minutes of regular power run due to extreme thermal stress With WEP on the MiG-21bis's R-25 engine produced a huge 10–12 meter long blowtorch exhaust with six or seven brightly glowing rhomboid "shock diamonds" visible inside the exhaust The Russians gave the emergency power setting its "diamond regime" name never used in India Given a skilled pilot and capable missiles it could give a good account of itself against contemporary fighters Its G-limits were increased from +7Gs in initial variants to +85Gs in the latest variantsKrál Martin "MiG-21BIS" Soviet Hammer 6 April 2012 Retrieved 28 June 2012 It was replaced by the newer variable-geometry MiG-23 and MiG-27 for ground support duties However not until the MiG-29 would the Soviet Union ultimately replace the MiG-21 as a maneuvering dogfighter to counter new American air superiority types