I need better brakes!

[KaDuWin]

LOL sorry for the confusion, I was referring to both. My car was built before they started to use a more common MC which they started using in Oct of 91 which is why its so simple for you to find the MC for you 91. Because mine was built as early as it was, Toyota had a different design for the MC in the very first chassis's that were built.

I was just trying to describe what 2 Toyota dealerships told me along with another after market parts website told me. Everyone else (parts distributors) I tried had no idea why they didn't have the right MC for my car. It wasn't until I had my Vin matched at the Toyota dealer which I got the part from, that I learned why it was so difficult to get the right MC for the very first MK2 to be produced.

In short Toyota had a different design for the MC of the MK2 produced from Jan 1990 through Sept 1991. In Oct 1991 they switched to a more common and perminent design which they continued to use in for production of the MK2.

[karl]

Originally Posted by TomsMR2

its not less aggressive. turbo brakes have more piston surface area.. you have to change the prop valve to get properly balanced brakes.

no they don't. NA calipers use a single 50.8mm piston, turbos use twin 36mm pistons. they share the same rear caliper and rotors. there is only a 0.4% difference in front piston area between the NA and turbo (which gives the turbo more front bias). the difference is insignificant.

in addition, the brake bias on the MR2 is determined by the piston area ratio front:rear and the effective rotor radius front:rear. the prop valve has little to do with determining bias, it is there to prevent the rear brakes from locking first on a threshold stop.

the NA prop valve begins to limit pressure to the rear circuit at ~430psi, while the turbo valve begins to limit pressure at ~800psi. what this means is you need to be on the turbo brakes about twice as hard before the prop valve kicks in. this is because the rear of the turbo cars weighs more, and under braking retains more traction than the NA. the initial bias built into the systems is almost exactly the same, and is desireable since having the rear brakes initially come on strong improves stability under normal driving conditions.

but under normal driving conditions, the prop valve does nothing. in order to generate the 430psi necessary to get into the range where the NA prop valve is active, you need to be pushing the brake pedal with about 65lbs of pedal pressure (given the pedal is about 4:1 leverage, stock 7/8 master cylinder, it's about 94lbs of pedal pressure with the MC you and I are running).

im using it too.. after 2 years i realize im really just pushing my foot real hard for the same amount of braking. its unnecessary, and wasted effort. i strongly dont recommend it to anyone for any reason (on stock brakes). you just dont need that much modulation!

it's a matter of preference really. maybe your definition of 'real hard' is a bit different from mine, but even my wife didn't notice anything 'real hard' about driving the car after i did the swap.

either way, i wouldn't go back to a smaller MC if someone paid me.