finally found good explanation (don't know who is author):
"Although at first it seems confusing, in fact the way that Alfetta front suspension vertical adjustment works is quite simple.
The lower wishbone has an effective radius of rotation of about 300 mm. You can’t really check this on your car because you can’t actually locate the position of the neutral axis of the wheel relative to the suspension mounts. However using 300 mm and calculating the ride height change gives a number that agrees with Haynes and other manuals. All Alfettas are the same, other variants are slightly different. I have a table somewhere which shows eight different torsion bar configurations applicable to other models.
A circle of 300 mm radius has a circumference of about 1880 mm. For our purposes a small section or arc of this circle can be taken to approximate to a straight line, so an arc of say 1 degree would correspond to a vertical movement of the wheel of about 5.2 mm. Don't worry about the 300 mm, just trust the 5.2 mm figure.
The suspension set-up has torsion bars running fore and aft on each side of the car, each bar having 35 splines at the front and 34 at the rear. Rotating the bar by one spline at one end will turn the lower arm by either one 34th or one 35th of a circle, i.e. about 10.3 or 10.6 degrees, changing the ride height by about 53.5 or 55.1 mm. This is probably rather more than you need unless you have something unusual in mind for your car.
However turning the bar at both ends will result in a change in the ride height by an amount which is the difference of the two figures, i.e. by one over (34 times 35) of a circle i.e. about 0.3 degrees. This would give a ride height change of about 1.6 mm (the difference between 55.1 and 53.5 mm).
You can see where this comes from if you think of it in two steps. First, rotating the bar by one spline at the rear (fixed) end would raise the ride height by 55.1 mm, and the corresponding movement of the torsion bar relative to the lower suspension arm would lower it by 53.5 mm.
Now we are in business. By dividing our required ride height change in mm by 1.6 (to the nearest whole number), and rotating both torsion bars by that number of splines at both ends we can adjust our ride height to meet our requirements fairly exactly.
Because the rear end has less splines than the front, rotation of the bar has more effect at the back than at the front. This is good news for us (maybe it was even designed that way) because it makes the direction of rotation that we should use intuitive. Turning the bar “down” will raise the ride height, and turning it “up” will lower it."
now I need to calculate "turns" to lower it for 40mm...