My car did NOT have a proportioning valve, front or rear.
It is without a doubt the most important thing that I have done to my car.
In the rear a single brake line comes into a T and than routes to the right and left calipers.
Same in the front. I put the adjustable proportioning valve ahead of the T, thereby effecting both front calipers.
Where to put it was a simple decision although I knew that rear drive cars had them in the rear. In my case, the front brakes would lock up under hard braking. so I put it there. It works very well. Add that to the softest brake pads that you can get from a race supplier and you will have great brakes.
I have not done it but I think that adding a residual valve to each caliper would be a big improvement.
Has anyone done that to a Mangusta?
DICK RUZZIN