Good write up. I've never owned a car with an adjustable proportioning valve, that I know of at least. ERAs use dual master cylinders with an adjustable bias linkage which, when properly set up, supposedly gives you true linear proportioning, or so I'm told. I can't say I've ever measured them. I would think Kirkhams use a similar set up. Even with cars that do not have an undercarriage brake box, a dual MC bias linkage wouldn't be all that hard to fabricate in. If you were doing any sort of serious racing in your car, why wouldn't you want that? Or if you're manufacturing a Cobra that's approaching six figures as a turnkey, why would you even
think about using a proportioning valve instead of a dual MC bias linkage? Tilton MCs are less than a hundred bucks a pop, and linkage is just linkage....
