Erich,
How do I factor in the area of the pistons into my calculations so I have a
better idea as to how much pressure is actually being applied to the disc to
stop the car. Do I multiply the psi times the area of the pistons in my
calipers?
Dan
---- e.coiner@cox.net wrote:
> Dan,
> Only one correction. The area of the pads is irrelevant to force
>calculations. You need to know the area of the pistons in the caliper. Only
>count the area of the pistons on one side of the disc. ie a 4 piston caliper
>only count the area of 2 pistons.
> Erich
> ---- deiland1@elp.rr.com wrote:
> > I've been doing more research on my brake upgrade and the following is what
>I
> > have found so far. If more knowledgeable souls are out there, I welcome
>your
> > input/criticism/outright yelling at me or what ever input you would like to
> > give.
> >
> > I can't get to the pedal box very well since it is mounted to my car, but
>based
> > on my crude measurements I think the pedal ratio is close to 4:1 if my
> > measurements are correct. The formula for calculating Master Cylinder line
> > pressure is:
> > Pressure = (Leg force on the pedal) x (Pedal Ratio) divided by (Master
>Cylinder
> > Piston Area).
> > Just for comparison's sake I'm using 100 for the leg force on the pedal.
>Actual
> > pressure may be more or less.
> >
> > 0.7500" bore MC = 0.4418 sq. in of piston area
> > 1.0000" Bore MC = 0.7854 sq. in of piston area
> >
> > Therefore; OE MC with .75" bore P= (100 * 4.33)/0.4418 = 980 psi
> > New MC with 1.0" bore P= (100 * 4.33)/0.7854 = 551 psi
> >
> > With the original 7" single diaphram booster you would gain about 494 psi
>of
> > free boost on the OE MC and about 381 psi with the 1" bore MC. But with the
>dual
> > diaphram MC this would increase to around 490 psi free boost. This means
>the
> > total boost are as below:
> >
> > OE 0.75" bore with 7" SD booster 980psi + 494 psi = 1474 psi total
> > New 1.0" bore with 7" DD booster 551psi + 490 psi = 1041 psi total
> >
> > Although this is about a 40% difference, when you consider the OE
>application
> > was with a two piston caliper with about 3.3 sq/in of pad area compared to
>my
> > new 4 piston caliper with 6.63 sq/in of pad area and slotted discs then the
>end
> > result is actually improved braking over the OE even with the 1" bore MC.
>If I
> > use a smaller bore MC with all my new parts I would really have a lot more
>force
> > at the brake disc which may actually not be that great of an idea.
> >
> > I have thrown out my calculations for all to see (flawed or not) and now I
>wait
> > the gunfire.
> >
> > Dan Eiland
> > _______________________________________________
> >
> > tigers@autox.team.net
> >
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