DrMotor

Well, we DO have direct admissions from: BMI-Models,Common-Sense-RCand also Extreme Flight, that their motors are all made in the Sunray Technology factory. That is something you cannot possibly argue with, siberianhusky.
Also, we now know for certain that PA Thrust motors aremadeat Sunray Tech; And it is very revealing that BMI Spitz motors and PA Thrust both claim to use"High Velocity Forced Cooled Ventilation (HVFCV)" -This doubtless indicates there mustbe great similarity between these motors internally, even if the outside is slightly cosmetically different.
-And it has been realised very widely for a few years now, that Hacker motors are identical (apart from cosmetic appearance) to E-F Torque and to Z-Hyperion motors, and that they are all made together in the same (Sunray) OEM factory. It would seem pure folly,siberianhusky, to attempt to argue against this widely accepted fact.

siberianhusky: Please point out where the Kv of equivalent Sunray OEM motors (from different Sunray brands), differs by 200 rpm / V. On the contrary, itseems to me that the Kv's matchup extremelywell, within about 20 or 40, and thatis the best that can be expected from Kv. In many cases, the Kv's of equivalent Sunray OEM motorsarealmost identical.
ALSO: Do you really believe the absolute accuracy of each quoted Kv,by each motor brand ...?-It is quite obvious that some of the brands(-like LiPolice, Foxy and Shulman Fury) have anyway simply quoted the Kv given to them by the manufacturer, ratherthan doing any measurement themselves...
And also, it is quiteclear that OK Hobby have usually changed the Kv value by 10, 30 or sometimes >80, from the original Sunray manufacturer value, simply to give the illusion thattheir brandmight be a little different spec fromother identical motorslike e.g. LiPolice or Foxy ...

Also should be realised: That Kv is the "specific no load speed"and is just a theoretical value -true Kv can never be actually measured, because a motor cannot be in a totally zero-load condition, and also internal resistance (Rm) and motor losses prevents true Kv measurement.
Kv is usually only calculated -by making V and I measurements with 2 props, and putting the figures into a program, such as DriveCalc.
Other people actually measure ns -the "real world specific no load speed" -and this does include motor losses. ns is always slightly less than calculated Kv.
Some retailers justmount a small piece of marked plastic on the motor shaft, and take a tacho reading with the motor running at known V, and then calculate Kv =Rpm / V Clearly this will be a very poor and inaccurate Kv, and cannot be regarded as a serious measurement.
So the conclusion is: We cannot really believe the absolute accuracy of any quoted Kv ... The fact that the quoted Kv of some identical motors might vary by 20 or 50 isof no real consequence at all, and is best taken with a pinch of salt...