Originally Posted by
zip439
The thing is we are talking volume, not area. Volume is radius squared times height, thus the master cylinder must travel exponentially to make up for the increased volume not just for one piston cylinder but for four pistons in the larger front calipers. Say the NA is 2 and the SRT is 2.2 in diameter. 2 x 2 =4 but the SRT is 2.2 x 2.2= 4.84. Now .84 x the four pistons would mean the same master cylinder must move 21% more fluid to fill the cylinders. 19.36 vice 16. Everything else being equal the travel of the brake peddle travels 21% farther. That's a bit simplified, but you get the idea. I am no mathematician, so I maybe all wet.
Wish you had more than one other SRT 6 to compare with your car. Plus each car is a little different and even more so with the passing of time.
I am sorry but you failed the maths test, area is = pi x r x r.
I said the pistons only move a few thou, they are practically rubbing lightly all the time.
The seals pull back the pistons by returning to their original shape also the seals are pushed back by any wobble in the disk, it is hard to have a disk rotate without a few thou runout. Too much runout and you feel it in the brake pedal.
Pushing the brake pedal initially takes up the slack in the mechanism, the amount the MC piston moves is about 1/8” to 3/16” from what I remember, if the area of the pistons was twice that of the NA then the movement would be at the most 3/8” and that would not account for the massive pedal drop that happens. As I said with the ignition OFF the pedal works fine and does stop the car from rolling albeit with greater pressure on the pedal.
I have tried another SRT and the owner of it says my pedal drops too much.
I will update my figures later, as I have to go out.
Edit
I did the calculations but lost them, the extra volume of oil moved is about 50% more as I recall.