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Thread: Comparitive subie front calipers

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    Comparitive subie front calipers

    Anybody know where I can find the table comparing "swept area" for Wrx front calipers of various years? I have '02 WRX calipers on front of my 818S, need to decide which calipers to use to improve rear beaking.

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    Quote Originally Posted by tmoretta View Post
    anybody know where i can find the table comparing "swept area" for wrx front calipers of various years? I have '02 wrx calipers on front of my 818s, need to decide which calipers to use to improve rear beaking.
    tom on one my 818 i used 06 legacy gt front and rear rotors and calipers lot bigger and rears are vented and bolt right on

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    Is the Legacy GT front caliper larger than my current '02 WRX front rotor? I already have H6 rotors in rear of my 818, I would like to be able to use them.

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    Senior Member Bob_n_Cincy's Avatar
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    This is what is in the service manual:

    Attached Images Attached Images
    Last edited by Bob_n_Cincy; 04-18-2019 at 02:41 AM.
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    Isn't there a difference in size/swept area in various WRX brake caliper models 2002-2008?

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    Senior Member Bob_n_Cincy's Avatar
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    Quote Originally Posted by tmoretta View Post
    Isn't there a difference in size/swept area in various WRX brake caliper models 2002-2008?

    From the rockauto page, it looks like the same rotor was used from 2002-2010
    brakess.jpg
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    What about the diff. in piston area between 2 pot and 4 pot front calipers?

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    Senior Member Bob_n_Cincy's Avatar
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    Quote Originally Posted by tmoretta View Post
    What about the diff. in piston area between 2 pot and 4 pot front calipers?

    The impreza 2 piston sliding caliper has 1.685 diameter piston. Which is 2.230 square inches times 2 is 4.460 square inches.
    The master cylinder is 1.0625" diameter piston. Which is 0.887 square inches.
    Master cylinder to caliper squeeze gain is 4.460/0.887 = 5.030

    The wrx 4 piston fixed caliper has 1.591 diameter piston. Which is 1.988 square inches times 2 is 3.976 square inches.
    The master cylinder is 1.0" diameter piston. Which is 0.785 square inches.
    Master cylinder to caliper squeeze gain is 3.976/0.785 = 5.062


    As you can see the caliper squeeze force gain is very close between an impreza and impreza WRX.

    Bob
    Last edited by Bob_n_Cincy; 04-19-2019 at 12:19 PM.
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    On the 4 piston caliper, isn't the math 4 times the 1.98 square inches?

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    Quote Originally Posted by tmoretta View Post
    On the 4 piston caliper, isn't the math 4 times the 1.98 square inches?
    No, but it's hard for me to explain.
    On a 4 pot system, 1/2 is the applied force and 1/2 is used as reaction force.

    On a 2 pot system the pots are the applied force. The back side of the pots push the sliding caliper resulting in that reaction force being applied to the outside pad.


    Bob
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    Thanks Bob.

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    Quote Originally Posted by tmoretta View Post
    Anybody know where I can find the table comparing "swept area" for Wrx front calipers of various years? I have '02 WRX calipers on front of my 818S, need to decide which calipers to use to improve rear beaking.
    i'm running 06 front calipers at all 4 corners. sti rear rotor. had to make spacers, re locate mounting holes, and have ebrake shoes made. if youre handy, I guess this is the cheapest way to get big rear brakes.

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    Quote Originally Posted by 20boxer View Post
    i'm running 06 front calipers at all 4 corners. sti rear rotor. had to make spacers, re locate mounting holes, and have ebrake shoes made. if youre handy, I guess this is the cheapest way to get big rear brakes.

    I have the same as 20boxer except I am running the DBA rear rotors. Just to be clear, we are running the 2 pot sliding front calipers on all four corners. I have run about a dozen track days with no problem with any brake fade. This setup gives me 150% of braking capacity over standard Impreza with a car that weighs about 60% of a standard Impreza. I am using some Powerstop street performance pads. The have plenty of grip but do emit a lot of brake dust. https://www.powerstop.com/product/power-stop-z26/
    Last edited by Bob_n_Cincy; 04-20-2019 at 08:34 PM.
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    I will be ordering a pair of two pot front calipers to use in the rear over the H6 rotors that I already have. I know that I will have to re-drill the mounting holes in the rear backing plates and use spacers in the rear calipers to avoid having the pistons run out of travel. I will also trim some friction material from the outside of the rear brake pads so they don't overlap the outer edge of the H6 rotor. Anything else?

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    Senior Member Bob_n_Cincy's Avatar
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    Quote Originally Posted by tmoretta View Post
    I will be ordering a pair of two pot front calipers to use in the rear over the H6 rotors that I already have. I know that I will have to re-drill the mounting holes in the rear backing plates and use spacers in the rear calipers to avoid having the pistons run out of travel. I will also trim some friction material from the outside of the rear brake pads so they don't overlap the outer edge of the H6 rotor. Anything else?
    Here is a picture of that setup. Notice how there is room for bigger rotors. IMG_20141013_173428719_HDRs.jpg
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    The rotors in your pic. don't look like my H6 units - yours is vented.

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    Senior Member Bob_n_Cincy's Avatar
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    Quote Originally Posted by tmoretta View Post
    The rotors in your pic. don't look like my H6 units - yours is vented.

    That picture is the first rotor I tried.
    https://www.rockauto.com/en/moreinfo...=1435927&jsn=1

    it was used on IMPREZA 2006-2007 and LEGACY 2005-2009


    Below is the picture of my current rear DBA rotors.

    brake_DBA.jpg
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    So the DBA is bigger diameter - does it require modified e-brake shoes?

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    Senior Member Bob_n_Cincy's Avatar
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    Quote Originally Posted by tmoretta View Post
    So the DBA is bigger diameter - does it require modified e-brake shoes?

    The DBA 2657 fits Impreza standard 170 mm e-brake and is 316mm diameter and 20 mm thick.

    dba_2657_cat_a.jpg
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    So the DBA 2657 is bigger diameter than my stock '02 WRX front rotors (276 mm)? Is that going to lock my rear brakes before front?

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    Quote Originally Posted by tmoretta View Post
    So the DBA 2657 is bigger diameter than my stock '02 WRX front rotors (276 mm)? Is that going to lock my rear brakes before front?
    The portioning valve would be moved to the rear to trim down the backs a bit. This almost unavoidable really. No rear Suby brakes are going to give you the stopping force required for a balanced setup.

    The other option vs. the expensive DBA rotors are thicker ebrake shoes (godspeedbrakes in the UK sells them), and standard '04 STI rear rotors (can get blanks for $40/per).

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