I pulled an old reservoir, from my pre-power assist days, from my storage clutter. The kind which mounted on the left inner fender well chassis. Lo and behold, its overflow/air admittance orfice faces the rear of the car!
Can I mount this one where the power assist goes? No, it would stick up too high, things point the wrong way, maybe if I changed out the short hoses and fabricated a bracket it could. Besides, it was getting brittle, and the overflow nipple had broken off so it would need repair. One of the pictures shows how it is configured, though. I think it would be possible to use the old reservoir and mounting, and use longer hoses to connect to the master cylinder.
How about just turning the stock power assist reservoir 90 degrees? Well, that runs into the same general issues about bumping into the vacuum pan and hose lengths and hood clearance. But with enough effort and modification I suppose it could be made to work with a modified bracket and hoses. Though the angle of the hose outlets on the non-power reservoir could make this tricky..
How about I use my pressure bleeder cap, which is a stock cap with a tire nipple coming out the top - just pull the Schraeder valve and attach a hose? Well, the issue here is clearance from the hood. There isn't enough. And I didn't have anything to make a right angle screw-on cap with. With something like that and using a super short tire nipple, perhaps this would work.
Ok, off to the junk box (actually a bunch of those plastic drawers where I try to keep nuts and bolts and smallish parts in some semblance of order). What't this - a nice 90 degree sort of fitting. Don't know where it came from, but at one time its function for me was to spray water onto the top of the engine oil cooler - a Mazda oil cooler mounted in the center of the front valance did away with the need for this.
As an added bonus, the cap has a sort of disk like cover inside over the center of the cap, which snaps on. It has a couple of small holes in it. When removed, there is a dimple in the exact center of the cap, which is under a center protrusion on the top outside of the cap. The dimple is ideal for centering the hole to be drilled. And the little cover forms a small space, with the little holes restricting what comes into or goes out of this - perhaps it will reject slosh, but allow air in and out as needed.
To make absolutely sure I didn't have clearance issues, I sank the reservoir down into its mounting. Bend the metal strap some and rebend, and use a longer bolt. Might not have been necessary, but I didn't want to try to get in the trunk and close the lid on myself to see, and couldn't figure out how to use my boresccope.
So here is the result.
At some point I may bestir myself to create a more elegant method of holding the catch bottle. But I know this works, so that may be quite a while as such things go.
It will be mid-September before we get the car back on the track to see how well or poorly this works. Given that these problems never happened with the car and driver in pre-power assist mode, and at one point I used slicks on the car, I am inclined to think that it is the position of the air inlet/overflow which causes this to be a problem for those of us who track or autocross the cars.
Fact is, our cars will brake just fine with no fluid in the reservoir, as long as there is still some in the line. No reserve for pad wear there, or to deal with a little leakage from a wheel piston seal, etc. But in the short term you don't need a full reservoir. So at some point you can reduce the level to the point where eveh high G cornering isn't going to lead to fluid being pushed out.
But I just feel better with a full, or nearly full, reservoir while on the track or at an autocross.