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Why would you want to put residual pressure valves in -line after the master cylinder? I know it might help with having to not pump the brakes to get the pads back on the rotors, but wouldn't it cause some drag and maybe inconsistency? Why a dual cylinder on a 2 wheel vehicle?
see picture:

I have them on my car as well. It doesn't have any brake drag and yes, it keeps the brake pistons from retracting and me having to pump the brakes to get a pedal. I'm willing to bet that car has duel calipers on the rear which is why they plumbed it like that
Chuck

While firewall mounted master cylinders don't benefit much from residual valves , frame mounted ones that are lower than the caliper can maintain a firmer , more confiftant pedal with a 2# valve .
I suspect on a car with dual calipers , a little drag is not a concern .

Back in the '90's I bought a Comp car from a championship team that had them.
It had residual valves that were located back on the rear end housing.
It had one to each caliper after the Tee on the housing. I have always wondered why it was done that way. For a car that had the dual (front brakes,too) master cylinder mounted down low on the frame rails it worked well. Still needed one pump to get a pedal with feel & the brake pressure gauge to respond. Another thing I found that was interesting was a brass cup that was placed in one of the fittings on the master cylinder side of the line lock. It had a .060 hole in it for fluid flow. I just figured it was a poor mans proportional valve. Could the cup plug have been there to place a little drag on the front brakes as the line lock was released? In dealing with Stick cars I know that a little "hold or drag" on the front brakes helps set the rear suspension & clutch. That usually helps E.T., too.
I'm going to plumb a Roadster I've had for some time. I've decided it's primary use will be for local index and bracket races.
Thanks for the replies. I'm sure they helped.
FWIW: any more ideas will be appreciated, too.
Adger Smith