The SR-71's J58 engines were most efficient at around Mach 3.2, since only 20% of the thrust was created by the engines, while the remaining 80% was done by Ramjet thrust where the spikes in front of the engine intakes would create a supersonic shockwave and would be fed into the outer part of the engine by the spikes retracting about 20 inches.
Max speed: Mach 3.4 (2,244 mph) at 80,000+ ft
Records:
absolute speed record of 1905.80993 knots (2,193.1669 mph) and
"absolute altitude record" of 85,068.997 feet
2200 mph
3.5
Stratosphere
About 3 times the speed of sound. (3 mach)
SR71 Blackbird Model M-21: maximum speed: 2211miles/h Generally, the given answer for all models of the SR71 is: "In excess of Mach 3", or more than three times the speed of sound. see related links below for more info
Black
The SR-71 Blackbird is 2,193 miles per hour fast or Mach 3, three times faster than the speed of sound.
2193 mph
The SR-71 Blackbird was introduced into service in 1966.
It is the Lockheed SR-71 "Blackbird", a reconnaissance aircraft.
They can fly at over Mach 3.5 .
No it just flew very high to avoid radar.