Only a couple of years ago boosterless brake (manual brakes) setups were considered impractical because the available designs offered by vendors were single master cylinder brackets that protruded the MC into the engine bay. The problem was that one master cylinder cannot provide leg pedal pressure that is soft enough for daily driving, or even comfortable spirited driving, the result is a very firm brake pedal intended for the track.
Master cylinders come in various bore sizes, and the general rule is that the smaller the bore the more it will travel and thus will require less leg pressure to operate.
To achieve street-able leg pressure you have to run two master cylinders for the brake and one master cylinder for the clutch. At the time the only way to do that was to use Tilton style floor mounted dual master cylinder setups which placed the pedals in an uncomfortable non-oem feeling position closer to the driver seat.
The general consensus at the time was that even with two master cylinders the leg pressure would still be non-street-able and there was no way of making an OEM feeling dual master cylinder setup in an E30.
This common mentality changed drastically for two reasons:
1. The concept of inverting the master cylinders to sit in a bracket on the inside of the car in the pedal area instead of protruding into the engine bay.
2. I was able to mathematically prove that with two 5/8″ (.625 mm) bore size master cylinders and 6.25:1 ratio pedals from Wilwood (or other) the leg input pressure would be under 60 pounds. A regular person can usually apply 120 pounds if needed, street cars are normally in the 40-60 pound range with brake boosters, and track setups aim to be around 80 pounds. This all meant that with the setup aforementioned manual brakes could easily and comfortable be used on a street car.
For those interested in calculating for themselves:
To my knowledge three different parties create bracket systems allowing for the inverting of the master cylinders.
The first person to achieve this was Titus Amza in 2011, his website now is overshadowed by other vendors and does not come up very high on google results. As a result of being the mastermind behind the design I hope this article will shed some light on his creation, website and offering. At the time I discovered his design, the bracket he was offering was a weld it yourself type for $103.30 as he was injured and unable to weld them himself (he had sold welded versions prior). He has now been selling and continues to sell a fully welded ready version of his mount for $149 + shipping.
The second party to offer this bracket for sale was Garagistic in 2013, the design looks very similar to me; I am not sure what kind of collaboration (if any) there was with Titus. I was able to get my hands on a bracket from the Garagistic guys and can confirm it is a quality made piece with clean welds, clean bends, all bolts & nuts included as well as a bracket for the brake switch and a small support bracket for the firewall. They offer theirs for $175, or $195 powder coated. The guys seem top notch and the offering seems to be a nice complete solution; they also have a guide on their website on how exactly to alter the wilwood pedals to work with their bracket.
The third option is the “DTM pedal box” from Massive Brakes. This design is different from the previous two, and although it is offered at $450 CAD, it already includes the brake pedal, linkages and pedals. With the previous two options you would still need to buy the wilwood brake pedals at a cost of $225, so keep that into consideration when considering the price of this option.
All require you to purchase master cylinders separately (of your choice and bore size). The most common pedal setup used for the first two brackets is wilwood part number 340-11299.