New pic:
Ok, pic is horrible, one can't see how it has actually smooth transition from side to top and how sides are pulled inside at least 15 degrees, top is perhaps around 9 degrees, I did estimate measure 5cm drop in 50cm distance, so that is 10% and if 90 degrees is 100% drop, then 10% must be 9 degrees, but that can be awfully wrong thinking, I'm not good with angles and measuring, so I did build whole thing by eyeballing it.
So with my latest coast down test, I had ended up to cd of 0.429, which can be possible, because end of front bumper is missing so from bumper air meets inner fender and tire, also no spare tire means that rear bumper is like a parachute.
Same road, but this time road was bit wet, which might cause poorer results than with same conditions as before, one pass to both directions and I got result cd 0.308 which might be bit too good, or maybe not, if I calculate right that is 28.2% improvement, but there is also now upper grille block in place too.
Subjective estimating is that wind does not grab car so much, car is also a lot more quiet, not much wind noise anymore.
I can coast down on places where I could not before.
I did make new fillup even I had not driven much, only 104km driven, from those around 50km with kamm. 4.56l/100km which includes quite many cold starts too. There is difference of 0.54l/100km and if that is because of kamm, then it would reduce consumption by 1l/100km, but that is as good method as lottery for estimating anything.
I always fill up so that diesel stays on ring that is at filler neck, also I put fuel in very slow and use same meter and same position of car, as I attempt to reduce errors from filling, but it is not still 100% that I get similar way of fillup each time.
Upper grille block is also affecting that result, so is ram air pickup, which is perhaps more of cold air pickup, but at least it is under the bumper at the air stream, whatever good that will do.
Upper grille block seem to lift snow up so that it does not hit on windshield anymore, also rear window seems to stay bit longer clear than before, water drops seems not to be removed from kamm quite easily, after 20km test drive I still had them there, whatever that tells.
In rally ZX kit car, there seem to be similar plastic pieces at front of wheels as new bmw/mercedes cars have, I believe that if I can copy location, size and shape of those, then I might get some gains, when I put rear belly pan to car as air guided underside the car is at the moment causing lot of drag.
My aim is to get Opel Calibra level cd out from this car, but I don't know if that is realistic at all, but I can always try, also reliably in 3.5l/100km level fuel consumption or less in this hilly area is what I hope, maybe hitting as low as 3.2l/100km if weather is good and level roads, but that might be impossible.
Best thing so far is that reduced wind noise.