BB height when change 29er wheel to 27.5 wheel I have a 29er frame Specialized Camber Expert Carbon EVO with 330mm BB height with 120mm 29er fork

How much with the BB height be altered if I change to 650b wheels and 27.5 140mm fork?

EDIT

The fork length in 29er is 531mm from crown to axle, and the new 27.5 fork is 527.7mm

@Argenti Apparatus says that 19mm will drop with the rim 27.5, and the image says that with the new fork I will drop from 330 to 328.8mm

This mean that my new bb height with custom configuration will be 330mm - 19mm - 1.2mm? 309.8mm in total. This is low or very low? My loss will be 0.795 inch.



NOTE: all features in the part green in image is actual configuration

NOTE 2: about sag described for @mattnz ¿How this can help?
The change in rim size will drop the bike 19mm. 29" are ISO 622, 27.5 are ISO 584. (622-584)/2 = 19. If you run larger tires on the new wheels that difference will be less.

We cannot say what effect a fork change will have unless we know what the crown to axle distance of the two forks is. Knowing the travel (120 vs. 140mm) does not tell us anything about fork length.

Be careful if you are considering a different fork length as it will of course change the steering geometry of the bike. 



Update based on new data ...

Yes, those numbers add together, however, 3.3mm difference in fork length is negligible. The fork sag will be much bigger.

A drop of 20mm BB height from 330 to (approx) 310 is only 6%. Balance that against whatever benefit you are trying to get from smaller wheels.