BluePrint Engines

Visit our community sponsor

Thanks Thanks:  1
Likes Likes:  1
Page 1 of 2 12 LastLast
Results 1 to 40 of 74

Thread: Subaru 4 pot front callipers on the front and the rear?

  1. #1
    Senior Member DodgyTim's Avatar
    Join Date
    Apr 2013
    Location
    Brisbane, Australia
    Posts
    289
    Post Thanks / Like

    Subaru 4 pot front callipers on the front and the rear?

    Hi
    I thought I’d run a brake upgrade idea past you all for comments
    I have an 818R and I’m looking at cheap option to upgrade the brakes
    I’m not against the Wilwood kits, but if I buy one I’ll double the cost of the kit due to my wife’s revenge spending on shoes

    My build is using the 2006 WRX brakes at the moment, so
    Front = 295 dia x 25 thick rotors with the 4 pot Subaru callipers
    Rear = 290 dia x 18 thick rotors with the 2 pot Subaru callipers

    What I’m thinking of doing is upgrading the rear rotors with a DBA rotor part number DBA 42657 and fitting another set of Subaru 4 pot callipers to the rear (if possible).
    I already have the spare callipers, kindly donated by another 818 builder who purchased the full Wilwood kit

    The DBA 42657 is 316mm diameter and 20 mm thick. It keeps the standard 170mm dia handbrake.

    This rear 4 pot & larger rotor combo would provide 2.4 times more rear braking than the 2006 2 pots, and the total braking would be rear biased by about 7%.

    That sounded like too much rear brake, until I looked at the FFR offered Wilwood kit.

    The lower cost version of the wilwood kit has front and rear 4 pot callipers, with 12” front rotors and 12.19” rear rotors. Provided the front and rear callipers are the same, this is 2% rear brake bias.

    Thoughts?

  2. #2
    Mechie3's Avatar
    Join Date
    May 2012
    Location
    Indianapolis
    Posts
    5,174
    Post Thanks / Like
    Bob n cincy did this or something similar.
    Zero Decibel Motorsports
    Check out my new website!
    www.zerodecibelmotorsports.com
    www.facebook.com/zero.decibel.motorsports

  3. #3
    fasterer and furiouser longislandwrx's Avatar
    Join Date
    Aug 2012
    Location
    Long Island
    Posts
    2,540
    Post Thanks / Like
    Blog Entries
    6
    I was originally going to run small lightweight brakes in the back until I heard that people were having to dial down the front brakes to get more rear bias.

    If you are going to go with the 42657's instead of messing with a custom adapter why not get the rear Brembo calipers to match... I bet you could trade/sell your spare fronts and existing rears and buy some Sti takeoffs and the already made adapters
    for not much out of pocket. just a thought.
    Last edited by longislandwrx; 06-22-2015 at 05:56 AM.
    A well stocked beverage fridge is the key to any successful project.

  4. #4
    Senior Member
    Join Date
    Jun 2013
    Location
    Bowling Green, KY
    Posts
    1,382
    Post Thanks / Like
    Tim,
    My original plan was to do the same thing but I was going to run the front rotors on the rear (I deleted the e-brake on my R build)
    I have ended up going another direction and running the same AP calipers and 299mm rotors front and rear. With 57% rear weight and bigger rear tires is the logic I am using.
    Last edited by Mitch Wright; 06-23-2015 at 11:27 AM.

  5. #5
    Senior Member Bob_n_Cincy's Avatar
    Join Date
    Sep 2012
    Location
    Cincinnati OH
    Posts
    3,903
    Post Thanks / Like
    Be careful when you talk about 2 pot, 4 pot, 6 pot calipers.
    The effective diameter of the pots and rotor diameter is what is important.
    I am running 2 pot 3.37" in the front and rear.

    The 06 2 pot impreza front is 3.37"
    the 06 4 pot WRX has 3.082" front
    The 06 4 pot STI has 3.386 in the front.

    The 06 1 pot impreza has 1.5" in the rear.
    the 06 2 pot WRX has 1.5" in the rear
    The 06 2 pot STI has 1.417 in the rear.

    I have more than twice the clamping force as the wrx or sti rear brakes.
    With no portioning valve and square tires, my rears lock up just before my fronts. (this is a bad thing)
    I am installing my wider rear tires and will test again. If problem remains the I will add proportion valve on rears.

    br.jpg

    IMG_20141013_173428719_HDRs.jpg

    Bob
    Last edited by Bob_n_Cincy; 06-22-2015 at 08:34 PM.
    818S #22 Candy Blue Frame, Front Gas Tank, 2.5L Turbo, Rear radiator, Shortened Transmission, Wookiee Compatible, Console mounted MR2 Shifter, Custom ECU panel, AWIC soon
    My Son Michael's Turbo ICE Build X22 http://thefactoryfiveforum.com/showt...rts-818S-Build
    My Electric Supercar Build X21 (on hold until winter) http://thefactoryfiveforum.com/showt...e-Build-Thread

  6. #6
    Senior Member Frank818's Avatar
    Join Date
    Jun 2013
    Location
    QC, Canada
    Posts
    5,732
    Post Thanks / Like
    Quote Originally Posted by DodgyTim View Post
    The lower cost version of the wilwood kit has front and rear 4 pot callipers, with 12” front rotors and 12.19” rear rotors. Provided the front and rear callipers are the same, this is 2% rear brake bias.
    They are not. The rears are smaller on that Wilwood kit. And I am unsure if you can fit the front calipers over the rear discs or if you need same front 12" fitted in the back.

    I am curious to see how you end up with anything (logic driving you to choose one thing over another) and what will be the results.
    Frank
    818 chassis #181 powered by a '93 VW VR6 Turbo GT3582R
    Go-karted Aug 5, 2016 - Then May 19+21, 2017
    Tracked May 27/July 26, 2017
    Build time before being driveable on Sep 27, 2019: over 6000h
    Build Completed Winter 2021

  7. #7
    Tazio Nuvolari wannabe Scargo's Avatar
    Join Date
    Nov 2013
    Location
    south-central CT
    Posts
    1,611
    Post Thanks / Like
    DBA's are heavy rotors. Don't know about Wilwoods. I like the idea of the same Suabru four pots front and rear. I just think you need some two-piece Gyrodisc rotors, or similar.

  8. #8
    Senior Member DodgyTim's Avatar
    Join Date
    Apr 2013
    Location
    Brisbane, Australia
    Posts
    289
    Post Thanks / Like
    Be careful when you talk about 2 pot, 4 pot, 6 pot calipers.
    The effective diameter of the pots and rotor diameter is what is important.
    I am running 2 pot 3.37" in the front and rear.

    The 06 2 pot impreza front is 3.37"
    the 06 4 pot WRX has 3.082" front
    The 06 4 pot STI has 3.386 in the front.

    The 06 1 pot impreza has 1.5" in the rear.
    the 06 2 pot WRX has 1.5" in the rear
    The 06 2 pot STI has 1.417 in the rear.

    I have more than twice the clamping force as the wrx or sti rear brakes.
    With no portioning valve and square tires, my rears lock up just before my fronts. (this is a bad thing)
    I am installing my wider rear tires and will test again. It problem remains the I will add proportion valve on rears.
    Thanks Bob, this is my math, but it needs to be checked

    The 2006 wrx front calliper has a working piston area of 3.97 square inches (2 pistons at 1.591 inch diameter)
    The 2006 wrx rear calliper has a working piston area of 1.77 square inches (1 piston at 1.5 inch diameter),
    so for the same brake line pressure, putting front callipers on the rear disk will give (3.97/1.77) 2.25x more rear braking.
    Then with the larger rear rotor (316mm vs the standard 290) that 2.25x clamping force acts on a 1.08 times longer arm, so I get the 2.4x (ish) increase in rear brake

    They are not. The rears are smaller on that Wilwood kit. And I am unsure if you can fit the front calipers over the rear discs or if you need same front 12" fitted in the back
    Thanks Frank, I haven't checked to see if the front callipers will fit without major modifications
    One big difference is the rotor width, the front calliper expects to see a 24 or 25mm thick rotor, but the standard rear rotor is only 18mm thick. This is one of the reasons I was looking to the DBA 42657 rotor, it is 20mm thick.

    DBA's are heavy rotors. Don't know about Wilwoods. I like the idea of the same Suabru four pots front and rear. I just think you need some two-piece Gyrodisc rotors, or similar
    I might look at this later on, when I have more cash available, and time in the car to work out what is the best spend for performance
    The DBA's are about $350 Aussie for each pair, so $700 total delivered
    The Girodisc's look to be about $700 US per pair, so with the lousy Aussie exchange rate = $1750 Aussie + delivery
    Last edited by DodgyTim; 06-22-2015 at 08:39 PM.

  9. #9
    Senior Member Bob_n_Cincy's Avatar
    Join Date
    Sep 2012
    Location
    Cincinnati OH
    Posts
    3,903
    Post Thanks / Like
    Quote Originally Posted by DodgyTim View Post
    Thanks Bob, this is my math, but it needs to be checked

    The 2006 wrx front calliper has a working piston area of 3.97 square inches (2 pistons at 1.591 inch diameter)
    The 2006 wrx rear calliper has a working piston area of 1.77 square inches (1 piston at 1.5 inch diameter),
    so for the same brake line pressure, putting front callipers on the rear disk will give (3.97/1.77) 2.25x more rear braking.
    Then with the larger rear rotor (316mm vs the standard 290) that 2.25x clamping force acts on a 1.08 times longer arm, so I get the 2.4x (ish) increase in rear brake


    Thanks Frank, I haven't checked to see if the front callipers will fit without major modifications
    One big difference is the rotor width, the front calliper expects to see a 24 or 25mm thick rotor, but the standard rear rotor is only 18mm thick. This is one of the reasons I was looking to the DBA 42657 rotor, it is 20mm thick.
    Hi Tim
    To solve the 18mm to 25mm thick rotor, I welded an old backing plate (1/4") to the backing plate of the outside pad.

    Here are some of the trimming I had to do to make things fit .
    IMG_20141012_205029097s.jpg

    IMG_20141012_205040000s.jpg
    Bob
    Last edited by Bob_n_Cincy; 06-22-2015 at 08:53 PM.
    818S #22 Candy Blue Frame, Front Gas Tank, 2.5L Turbo, Rear radiator, Shortened Transmission, Wookiee Compatible, Console mounted MR2 Shifter, Custom ECU panel, AWIC soon
    My Son Michael's Turbo ICE Build X22 http://thefactoryfiveforum.com/showt...rts-818S-Build
    My Electric Supercar Build X21 (on hold until winter) http://thefactoryfiveforum.com/showt...e-Build-Thread

  10. #10
    Senior Member DodgyTim's Avatar
    Join Date
    Apr 2013
    Location
    Brisbane, Australia
    Posts
    289
    Post Thanks / Like
    Bob, if the pad surface wears down to very little thickness, do you think it could come out of the calliper housing? or does your welded on piece act to keep it anchored?

  11. #11
    Senior Member Bob_n_Cincy's Avatar
    Join Date
    Sep 2012
    Location
    Cincinnati OH
    Posts
    3,903
    Post Thanks / Like
    Quote Originally Posted by DodgyTim View Post
    Bob, if the pad surface wears down to very little thickness, do you think it could come out of the calliper housing? or does your welded on piece act to keep it anchored?
    That is exactly why I did it. With the pad material gone. It cannot come out of the bracket.
    Also without this mod, the piston may come to far out of the caliper.
    Below, you can see why I put it on the outside pad.

    I wish the rotor as about an inch bigger in diameter.
    Bob

    IMG_20141012_205309322s.jpg
    Last edited by Bob_n_Cincy; 06-22-2015 at 09:12 PM.
    818S #22 Candy Blue Frame, Front Gas Tank, 2.5L Turbo, Rear radiator, Shortened Transmission, Wookiee Compatible, Console mounted MR2 Shifter, Custom ECU panel, AWIC soon
    My Son Michael's Turbo ICE Build X22 http://thefactoryfiveforum.com/showt...rts-818S-Build
    My Electric Supercar Build X21 (on hold until winter) http://thefactoryfiveforum.com/showt...e-Build-Thread

  12. #12
    818 builder metalmaker12's Avatar
    Join Date
    Mar 2012
    Location
    Exeter R.I
    Posts
    2,834
    Post Thanks / Like
    Blog Entries
    1
    The brakes you have are way more than enough
    818S frame #13 Jdm version 8 ej207

  13. #13
    Senior Member Junty's Avatar
    Join Date
    Dec 2013
    Location
    New Zealand
    Posts
    140
    Post Thanks / Like
    Hey Tim, I have previously suggested exactly your plan above - Bob also commented prior to completing his work also. My logic - not as mathematical as yours, is many other mid or rear engined sports cars with 50:50 weight bias have same from and rear callipers and rotors... My 818S has your stock standard setup, and has now completed full compliance and certification. So my next step is to improve brake performance, and I intend fitting the same 4 pot Subaru callipers from front to the rear of my car.
    The only question I now have - previously I also looked at fitting these with the same 316mm Brembo rotors (standard handbrake), is what Bob has mentioned regarding the total brake force applied from the sliding Subaru 2 pot fronts versus the 4 pot fronts? 3.37 versus 3.08? This could actually make the bias/balance perfect by fitting the bigger 2 pots to the front and adding the smaller Subaru 4 pot to the rear with the Brembo 316mm rotors????
    Does anyone know if any force/pressure is lost or compromised by the sliding action of the NA 2 pot front system? Why would Subaru increase to 4 pot with smaller force/area for the high spec vehicle? Is it merely cosmetic when you look through the 17inch wheels to see 4 pots?
    Note - my 818S has a functioning Subaru ABS system, but I definitely require significant improvement in braking ability. My R888's grip very well, and ABS doesn't actuate, but the car certainly needs to slow a lot better than it currently does.... Even though I don't actuate the ABS, the weight certainly tips the car forward, significant weight transfer to front - I want to feel the rear pull up harder, forcing the rear to squat.

  14. #14
    Senior Member Bob_n_Cincy's Avatar
    Join Date
    Sep 2012
    Location
    Cincinnati OH
    Posts
    3,903
    Post Thanks / Like
    Quote Originally Posted by metalmaker12 View Post
    The brakes you have are way more than enough
    Hi Metal,
    I agree the oem brakes are plenty for the 1800 lbs 818.
    But when most, if not all, decided to go without the booster, the braking was reduced by a factor of 6.
    See chart below.

    By moving the hole in the brake pedal arm increased the braking pressure by 30% (I guessed at this number)
    So the total braking force is about 1/4 the original boosted car with the same pedal pressure.
    It is even less than that if you put a proportioning valve in the front wheels.
    I increased the total braking force by 33% by my rear calipers mod.
    Bob





    booster.jpg
    818S #22 Candy Blue Frame, Front Gas Tank, 2.5L Turbo, Rear radiator, Shortened Transmission, Wookiee Compatible, Console mounted MR2 Shifter, Custom ECU panel, AWIC soon
    My Son Michael's Turbo ICE Build X22 http://thefactoryfiveforum.com/showt...rts-818S-Build
    My Electric Supercar Build X21 (on hold until winter) http://thefactoryfiveforum.com/showt...e-Build-Thread

  15. #15
    Senior Member Tamra's Avatar
    Join Date
    Apr 2014
    Location
    Shelton, CT
    Posts
    1,011
    Post Thanks / Like
    We are happy with our 2 pot and 1 pot calipers with EBC Yellow Stuff pads for autocross duty, both in terms of pedal effort and stopping ability. The car stops on a dime and we have to be conscious of not using the brakes too hard, as we can easily lock up the brakes. We adjusted the bias rearward and have the car braking fairly balanced now.

    Keep in mind it takes quite a bit of effort to properly bed in brake pads. They don't work well initially (I had to stand on the brakes and I still couldn't lock them up at first), especially since the brakes are manual. We bedded in our EBC Yellow Stuff pads in at an autocross school where we got a combined 60 minutes of race time. It took over half of the school before they really started working. Now they work great and I have to be conscious of how much pedal I use, else they will lock up.

    To be honest, I can't see why anyone would need "more" brake on the 818. OEM calipers with upgraded pads (if you are going to be performance driving) is more than enough in our experience. If you want lighter weight, by all means upgrade - we might in the future.

    For those who have upgraded, why do you think you needed bigger brakes? Did you give the OEM pads a try at all (and if you did, did you get them actually bedded in?)? I could see perhaps for real race use, needing more cooling and/or surface area.
    Last edited by Tamra; 06-24-2015 at 04:15 PM.
    Tamra
    Building 818SR #297 picked up 10/25/14 with Andrew (xxguitarist)
    First start 12/21/14, First "drive" 1/17/15
    First Dyno at EFI Logics 3/7/15- 310whp at 15psi for break in, full spool by ~3500rpm!
    First autocross 3/29/15
    1st Registered 818 in Connecticut 7/24/2015. 9 months - 1 day from kit pickup!

  16. #16
    Senior Member DodgyTim's Avatar
    Join Date
    Apr 2013
    Location
    Brisbane, Australia
    Posts
    289
    Post Thanks / Like
    Hi Junty

    I'm no guru on this stuff, so others may want to chime in too...

    I'm working on calliper piston area, where Bob seems to be working on diameter. I'm not sure which is correct

    The only question I now have - previously I also looked at fitting these with the same 316mm Brembo rotors (standard handbrake), is what Bob has mentioned regarding the total brake force applied from the sliding Subaru 2 pot fronts versus the 4 pot fronts? 3.37 versus 3.08? This could actually make the bias/balance perfect by fitting the bigger 2 pots to the front and adding the smaller Subaru 4 pot to the rear with the Brembo 316mm rotors????
    From Bob's chart, for the same brake line pressure, the floating calliper 2 pots will give more brake force than the fixed 4 pots. If you work on diameters it is +6%, if you work on area it is +12%

    So for the system you propose ( I think) is
    Front - floating Subaru two pot callipers (from the standard impreza) fitted on the WRX front rotors (294mm OD but 255mm effective)
    Rear - fixed Subaru 4 pots (ex 2006 fronts) on the DBA rear rotors (316mm OD but 266mm effective (guessed )
    This gives a 7% front biased system

    Apart from the rotor thickness issues, there is also the pad shape to consider. The 4 pots brake pad is only about 50mm wide, so the WRX rotor that suits that may not suit the 2 pot pad shape???

    I also measured the gap in the 4 pot calliper where the brake pads sit. On my callipers it is 28mm
    The brake pad backing plates are about 5 mm thick, and seem to need 2 mm or so engagement in the calliper.
    The DBA rear rotor is 20mm thick, but its minimum thickness is 18mm.
    This means that if my brake pads wear out I could have them come out of the calliper.
    The critical remaining pad thickness is 1mm (new rotor) or 2mm (worn rotor) which doesn't worry me too much given I'm not endurance racing
    photo.JPG
    Last edited by DodgyTim; 06-24-2015 at 04:15 PM.

  17. #17
    818 builder metalmaker12's Avatar
    Join Date
    Mar 2012
    Location
    Exeter R.I
    Posts
    2,834
    Post Thanks / Like
    Blog Entries
    1
    Quote Originally Posted by Tamra View Post
    We are happy with our 2 pot and 1 pot calipers with EBC Yellow Stuff pads for autocross duty, both in terms of pedal effort and stopping ability. The car stops on a dime and we have to be conscious of not using the brakes too hard, as we can easily lock up the brakes. We adjusted the bias rearward and have the car braking fairly balanced now.

    Keep in mind it takes quite a bit of effort to properly bed in brake pads. They don't work well initially (I had to stand on the brakes and I still couldn't lock them up at first), especially since the brakes are manual. We bedded in our EBC Yellow Stuff pads in at an autocross school where we got a combined 60 minutes of race time. It took over half of the school before they really started working. Now they work great and I have to be conscious of how much pedal I use, else they will lock up.

    To be honest, I can't see why anyone would need "more" brake on the 818. OEM calipers with upgraded pads (if you are going to be performance driving) is more than enough in our experience. If you want lighter weight, by all means upgrade - we might in the future.

    For those who have upgraded, why do you think you needed bigger brakes? Did you give the OEM pads a try at all (and if you did, did you get them actually bedded in?)? I could see perhaps for real race use, needing more cooling and/or surface area.

    Agreed 100 percent
    818S frame #13 Jdm version 8 ej207

  18. #18
    Senior Member DodgyTim's Avatar
    Join Date
    Apr 2013
    Location
    Brisbane, Australia
    Posts
    289
    Post Thanks / Like
    Quote Originally Posted by Tamra View Post
    We are happy with our 2 pot and 1 pot calipers with EBC Yellow Stuff pads for autocross duty, both in terms of pedal effort and stopping ability. The car stops on a dime and we have to be conscious of not using the brakes too hard, as we can easily lock up the brakes. We adjusted the bias rearward and have the car braking fairly balanced now.

    Keep in mind it takes quite a bit of effort to properly bed in brake pads. They don't work well initially (I had to stand on the brakes and I still couldn't lock them up at first), especially since the brakes are manual. We bedded in our EBC Yellow Stuff pads in at an autocross school where we got a combined 60 minutes of race time. It took over half of the school before they really started working. Now they work great and I have to be conscious of how much pedal I use, else they will lock up.

    To be honest, I can't see why anyone would need "more" brake on the 818. OEM calipers with upgraded pads (if you are going to be performance driving) is more than enough in our experience. If you want lighter weight, by all means upgrade - we might in the future.

    For those who have upgraded, why do you think you needed bigger brakes? Did you give the OEM pads a try at all (and if you did, did you get them actually bedded in?)? I could see perhaps for real race use, needing more cooling and/or surface area.
    Thanks Tamra, I appreciate the info. Do you use the proportioning valve in your build? to the fronts? Which brakes lock first?
    Cheers
    Tim

  19. #19
    Senior Member Tamra's Avatar
    Join Date
    Apr 2014
    Location
    Shelton, CT
    Posts
    1,011
    Post Thanks / Like
    Quote Originally Posted by DodgyTim View Post
    Thanks Tamra, I appreciate the info. Do you use the proportioning valve in your build? to the fronts? Which brakes lock first?
    Cheers
    Tim
    We did use the FFR proportioning valve. Without changing it, the fronts lock first and very easily. We dialed it rearward quite a bit until the fronts just lock slightly before the rears, but they are fairly balanced.
    Tamra
    Building 818SR #297 picked up 10/25/14 with Andrew (xxguitarist)
    First start 12/21/14, First "drive" 1/17/15
    First Dyno at EFI Logics 3/7/15- 310whp at 15psi for break in, full spool by ~3500rpm!
    First autocross 3/29/15
    1st Registered 818 in Connecticut 7/24/2015. 9 months - 1 day from kit pickup!

  20. #20
    Senior Member
    Join Date
    Dec 2014
    Location
    north east ct
    Posts
    160
    Post Thanks / Like
    if you are looking for big but stock brakes I went with 06-09 legacy gt frt and rear brakes ,the rears are vented and works real well I have not raced it but on the street it stops great

  21. #21
    Senior Member Bob_n_Cincy's Avatar
    Join Date
    Sep 2012
    Location
    Cincinnati OH
    Posts
    3,903
    Post Thanks / Like
    Quote Originally Posted by Tamra View Post
    We are happy with our 2 pot and 1 pot calipers with EBC Yellow Stuff pads for autocross duty, both in terms of pedal effort and stopping ability. The car stops on a dime and we have to be conscious of not using the brakes too hard, as we can easily lock up the brakes. We adjusted the bias rearward and have the car braking fairly balanced now.

    Keep in mind it takes quite a bit of effort to properly bed in brake pads. They don't work well initially (I had to stand on the brakes and I still couldn't lock them up at first), especially since the brakes are manual. We bedded in our EBC Yellow Stuff pads in at an autocross school where we got a combined 60 minutes of race time. It took over half of the school before they really started working. Now they work great and I have to be conscious of how much pedal I use, else they will lock up.

    To be honest, I can't see why anyone would need "more" brake on the 818. OEM calipers with upgraded pads (if you are going to be performance driving) is more than enough in our experience. If you want lighter weight, by all means upgrade - we might in the future.

    For those who have upgraded, why do you think you needed bigger brakes? Did you give the OEM pads a try at all (and if you did, did you get them actually bedded in?)? I could see perhaps for real race use, needing more cooling and/or surface area.
    Hi Tamra,
    I agree with what you did by increasing braking capability by going to a better pads.

    I like the performance of my brakes using
    https://www.rockauto.com/catalog/mor...php?pk=2022418

    Your method was a lot simpler.
    Bob
    818S #22 Candy Blue Frame, Front Gas Tank, 2.5L Turbo, Rear radiator, Shortened Transmission, Wookiee Compatible, Console mounted MR2 Shifter, Custom ECU panel, AWIC soon
    My Son Michael's Turbo ICE Build X22 http://thefactoryfiveforum.com/showt...rts-818S-Build
    My Electric Supercar Build X21 (on hold until winter) http://thefactoryfiveforum.com/showt...e-Build-Thread

  22. #22
    Senior Member Junty's Avatar
    Join Date
    Dec 2013
    Location
    New Zealand
    Posts
    140
    Post Thanks / Like
    Please could I have some feedback from other 818 builders like myself that are either go-karting or driving their cars? Aside from the active and interesting discussion regarding front versus rear callipers, without the brake booster (and following FFR build manual - moving the pivot position for brake) what is the pedal feel like? And how much pedal travel do you have with light verse heavy braking?
    My pedal is very firm, only get a small movement before pressure builds. So the pedal feels very hard, and as such I have very little adjustment beneath foot between hard and soft braking.
    What I'm proposing to do this week is change the stock WRX master cylinder from 1 1/16 diameter to 15/16. This should decrease fluid movement by about 20% - thus increasing both pedal movement and improving the feel of the brakes. Note: I have a huge amount of allowable travel before the pedal is near to firewall - so potentially I would almost change to 7/8 cylinder.
    This is trust and hope will also decrease the force required when applying the brake - especially without the booster?
    Feedback and thoughts welcome....

  23. #23
    Senior Member Tamra's Avatar
    Join Date
    Apr 2014
    Location
    Shelton, CT
    Posts
    1,011
    Post Thanks / Like
    Quote Originally Posted by Junty View Post
    Please could I have some feedback from other 818 builders like myself that are either go-karting or driving their cars? Aside from the active and interesting discussion regarding front versus rear callipers, without the brake booster (and following FFR build manual - moving the pivot position for brake) what is the pedal feel like? And how much pedal travel do you have with light verse heavy braking?
    My pedal is very firm, only get a small movement before pressure builds. So the pedal feels very hard, and as such I have very little adjustment beneath foot between hard and soft braking.
    What I'm proposing to do this week is change the stock WRX master cylinder from 1 1/16 diameter to 15/16. This should decrease fluid movement by about 20% - thus increasing both pedal movement and improving the feel of the brakes. Note: I have a huge amount of allowable travel before the pedal is near to firewall - so potentially I would almost change to 7/8 cylinder.
    This is trust and hope will also decrease the force required when applying the brake - especially without the booster?
    Feedback and thoughts welcome....
    Have you bed in the brakes yet? Ours required more effort (to stop quickly) than I weighed enough to produce before they were bedded in. Now they are great and very easy. We do have upgraded pads.

    Also, we prefer force modulated rather than travel (mushy) modulated brakes. That doesn't mean high effort though.
    Last edited by Tamra; 06-27-2015 at 07:38 PM.
    Tamra
    Building 818SR #297 picked up 10/25/14 with Andrew (xxguitarist)
    First start 12/21/14, First "drive" 1/17/15
    First Dyno at EFI Logics 3/7/15- 310whp at 15psi for break in, full spool by ~3500rpm!
    First autocross 3/29/15
    1st Registered 818 in Connecticut 7/24/2015. 9 months - 1 day from kit pickup!

  24. #24
    Member CNC_Geek's Avatar
    Join Date
    Feb 2013
    Location
    Southern California
    Posts
    95
    Post Thanks / Like
    Blog Entries
    2
    Just curious. Has anyone actually fit a stock Subaru brake booster onto the area provided? I tried and there was no physical space for this. Received my kit last April. Not sure if the chassis was redesigned from earlier 818 kits.

  25. #25
    Senior Member Bob_n_Cincy's Avatar
    Join Date
    Sep 2012
    Location
    Cincinnati OH
    Posts
    3,903
    Post Thanks / Like
    Quote Originally Posted by CNC_Geek View Post
    Just curious. Has anyone actually fit a stock Subaru brake booster onto the area provided? I tried and there was no physical space for this. Received my kit last April. Not sure if the chassis was redesigned from earlier 818 kits.
    CNC
    I don't know if this will help. These is the only pictures I have of the brake booster.
    Bob

    booster.jpg booster2.jpg booster3.jpg booster4.jpg booster5.jpg
    818S #22 Candy Blue Frame, Front Gas Tank, 2.5L Turbo, Rear radiator, Shortened Transmission, Wookiee Compatible, Console mounted MR2 Shifter, Custom ECU panel, AWIC soon
    My Son Michael's Turbo ICE Build X22 http://thefactoryfiveforum.com/showt...rts-818S-Build
    My Electric Supercar Build X21 (on hold until winter) http://thefactoryfiveforum.com/showt...e-Build-Thread

  26. #26
    Senior Member Junty's Avatar
    Join Date
    Dec 2013
    Location
    New Zealand
    Posts
    140
    Post Thanks / Like
    Thanks Tamra, Absolutely brakes are well bedded in. As with everything in my build I have new parts all around and included a higher spec set of pads (still stop when cold - with good heat range for track). I haven't yet tried drilled or slotted rotors.
    Also - I'm certainly not knocking the 818s stopping ability, it stops well. What I'm however looking for is incredible stopping ability. My 818s has a near new 2012 2.5L WRX engine with VF52 turbo - due to late model engine I've added Motec M800 ECU. It has a very conservative tune - on the dyno at 12PSI produces 247KW. It was also pushed a little harder to 16PSI and here was 287KW, but I want to learn more about the cars balance and drive before running the higher spec tune... We are lucky in Australasia that we have JDM spec Subarus. I'm sure you can imagine - this is a very rapid vehicle 0-100mph is phenomenally quick - I merely want the 100mph back to naught to be equally mind stopping! Note for USA HP folk - convert kw to HP by multiplying by 1.34, so 247kw = about 330HP (287 = 385).

  27. #27
    Senior Member xxguitarist's Avatar
    Join Date
    Nov 2013
    Posts
    389
    Post Thanks / Like
    Junty,
    With our 2 pot fronts, 1 pot rear, EBC Yellowstuff pads, we are able to lock up 245 Hoosier A7s.
    Unless you have HOT true race tires, or more tire width than fits under the car (more grip than DOT-R comps), there's no stopping any faster than we do.

    What's your problem with the existing brakes? Tire grip, brake bite & power, or eventual brake fade after repeated lapping?

    We would challenge that the first 2 aren't actually a problem. We aren't driving road course, so the third could catch up with you theoretically.

    On feel, it is much harder to modulate brakes that have variable pedal travel. I love brakes that have a tiny bit of take-up, then the pedal is dead solid, with just force modulation. Additional travel is asking for difficulty quickly modulating, and even more problems with heel-toe downshifts, since the brake pedal has different heights based on how hard you're braking. We don't have a low power car, either.
    -Andrew

    Building 818S/R #297 with Tamra
    08 Mazdaspeed3 | '12 F800R | '97 Miata

  28. #28
    Senior Member Junty's Avatar
    Join Date
    Dec 2013
    Location
    New Zealand
    Posts
    140
    Post Thanks / Like
    Hey Andrew and Tamra, thank you for feedback and support. My 818 stops well, and certainly if I stomp the brakes to haul up quickly - it will certainly lockup and R888's will slide (with ABS off). However I still want better braking - better pedal feel, and if I modulate the pedal I want it to stop so that it feels like I'm stripping the tarmac off the road - not just shreading/skidding tyres.
    So completed today - I have fitted 2 rebuilt 2 pot Legacy GT front callipers with new 294mm rotors. Ive also now finished installing my 2008 (4 pot WRX) front rotors to the rear along with DBA4657S rear rotors. These are slotted (couldn't get standard) with 170mm handbrake and 316mm diameter. Ive also fitted new HAWK Street/Race pads to front and rear. Finally I also fitted a new 15/16 master cylinder.
    Although still running all the setup in, it immediately feels great. Pedal moves a little easier - not as a boosted WRX - but has good gradual uptake for nice street driving - then with a little push brakes bite hard and pull evenly.
    Previously on other brake discussions/forums I've liked the concept of matching front and rear brake size and force. Similar to many other mid-engine or rear engine sports cars which have identical front and rear brakes. I now have (from Bob's calculations above) 3.37" brake calliper (force/area) front and 3.082" rear - with no brake bias.

  29. #29
    Senior Member matteo92065's Avatar
    Join Date
    Feb 2014
    Location
    Ramona, CA
    Posts
    417
    Post Thanks / Like
    I've been driving mine for 2 weeks now. I have STI Brembos w/yellow stuff on drilled/slotted rotors in front and Red stock WRX brakes in the back. ABS is on a switch. There are two proportioning valves on the front wheels.
    I can't get my rears to lock up. I know my system is very unbalanced. Due to vanity issues, I can't give up the Brembos and go to an Impreza caliper I am going to try the rear Wilwood 4 piston brake kit, #140-13013-DR. Gut feeling tells me it will be more balanced then, and look great.
    I should do the force/area calcs described above.

  30. #30
    Senior Member Bob_n_Cincy's Avatar
    Join Date
    Sep 2012
    Location
    Cincinnati OH
    Posts
    3,903
    Post Thanks / Like
    Quote Originally Posted by matteo92065 View Post
    I've been driving mine for 2 weeks now. I have STI Brembos w/yellow stuff on drilled/slotted rotors in front and Red stock WRX brakes in the back. ABS is on a switch. There are two proportioning valves on the front wheels.
    I can't get my rears to lock up. I know my system is very unbalanced. Due to vanity issues, I can't give up the Brembos and go to an Impreza caliper I am going to try the rear Wilwood 4 piston brake kit, #140-13013-DR. Gut feeling tells me it will be more balanced then, and look great.
    I should do the force/area calcs described above.
    Matt,
    Before you spend the money on the #140-13013-DR look at the piston diameter.
    They are design for stock Subaru and have only about half the braking force as the fronts.
    Bob
    818S #22 Candy Blue Frame, Front Gas Tank, 2.5L Turbo, Rear radiator, Shortened Transmission, Wookiee Compatible, Console mounted MR2 Shifter, Custom ECU panel, AWIC soon
    My Son Michael's Turbo ICE Build X22 http://thefactoryfiveforum.com/showt...rts-818S-Build
    My Electric Supercar Build X21 (on hold until winter) http://thefactoryfiveforum.com/showt...e-Build-Thread

  31. #31
    Senior Member matteo92065's Avatar
    Join Date
    Feb 2014
    Location
    Ramona, CA
    Posts
    417
    Post Thanks / Like
    Quote Originally Posted by Bob_n_Cincy View Post
    Matt,
    Before you spend the money on the #140-13013-DR look at the piston diameter.
    They are design for stock Subaru and have only about half the braking force as the fronts.
    Bob
    You're right. All the specs are about the same as stock WRX. Just the pad size gets bigger. Thanks.

  32. #32
    Senior Member xxguitarist's Avatar
    Join Date
    Nov 2013
    Posts
    389
    Post Thanks / Like
    Quote Originally Posted by matteo92065 View Post
    I've been driving mine for 2 weeks now. I have STI Brembos w/yellow stuff on drilled/slotted rotors in front and Red stock WRX brakes in the back. ABS is on a switch. There are two proportioning valves on the front wheels.
    I can't get my rears to lock up. I know my system is very unbalanced. Due to vanity issues, I can't give up the Brembos and go to an Impreza caliper I am going to try the rear Wilwood 4 piston brake kit, #140-13013-DR. Gut feeling tells me it will be more balanced then, and look great.
    I should do the force/area calcs described above.
    You say red WRX brakes in the back. Do they also have Yellowstuff pads, or do they have Redstuff pads? You could go down on the front pad if you felt it was necessary to shift the bias rearward more than you can accomplish with the prop. valve.
    -Andrew

    Building 818S/R #297 with Tamra
    08 Mazdaspeed3 | '12 F800R | '97 Miata

  33. #33
    Senior Member matteo92065's Avatar
    Join Date
    Feb 2014
    Location
    Ramona, CA
    Posts
    417
    Post Thanks / Like
    Quote Originally Posted by xxguitarist View Post
    You say red WRX brakes in the back. Do they also have Yellowstuff pads, or do they have Redstuff pads? You could go down on the front pad if you felt it was necessary to shift the bias rearward more than you can accomplish with the prop. valve.
    Yes, stock pads on the rear red colored calipers. I can see the confusion. There are so many combinations!

    So, maybe a harder compound in the front, and softer in the rear? Any recommendations?

    Wilwood does have three different calipers that would bolt right onto their system. Only difference being the piston areas, 1.58sqin, 2.46sqin, and 4.8sqin. The 2.46sqin looks closer to the 3.38sqin of the front than the current 1.50sqin.

  34. #34
    Senior Member xxguitarist's Avatar
    Join Date
    Nov 2013
    Posts
    389
    Post Thanks / Like
    Quote Originally Posted by matteo92065 View Post
    Yes, stock pads on the rear red colored calipers. I can see the confusion. There are so many combinations!

    So, maybe a harder compound in the front, and softer in the rear? Any recommendations?

    Wilwood does have three different calipers that would bolt right onto their system. Only difference being the piston areas, 1.58sqin, 2.46sqin, and 4.8sqin. The 2.46sqin looks closer to the 3.38sqin of the front than the current 1.50sqin.
    Wow, with Yellowstuff up front, and stock in the back, I'm not surprised you want more rear bias! That's even ignoring the larger calipers up front..

    We have yellowstuff all around, with 2 pot fronts, 1 pot rears. We were able to get balanced braking from a few turns of the adjuster knob. Lots of stopping force, with firm but reasonable pedal effort.

    Miata autox setup (no brake bias valve) says to correct the front bias, use one step down pad in front vs rear- red/green stuff front, yellowstuff rear, etc. The same can be done to correct bias on the 818 if your setup is beyond what you want to do with a Prop valve.
    -Andrew

    Building 818S/R #297 with Tamra
    08 Mazdaspeed3 | '12 F800R | '97 Miata

  35. #35
    Senior Member flynntuna's Avatar
    Join Date
    Apr 2011
    Location
    San Diego Ca 92106
    Posts
    1,972
    Post Thanks / Like
    Forgive the newb question. Are you saying you can adjust the bias front/rear by using different pads for the front and rear, fo instance stock front, yellow rear?

  36. #36
    Senior Member Tamra's Avatar
    Join Date
    Apr 2014
    Location
    Shelton, CT
    Posts
    1,011
    Post Thanks / Like
    Yellow Stuff pads are stronger than stock pads, so if you only put them on one end of the car, it would make that end have more braking bias.

    The FFR bias adjuster also can adjust the bias rearward, but since he put SO much brake on the front of the car and so little on the rear, it probably doesn't have enough adjustment to even it out.
    Tamra
    Building 818SR #297 picked up 10/25/14 with Andrew (xxguitarist)
    First start 12/21/14, First "drive" 1/17/15
    First Dyno at EFI Logics 3/7/15- 310whp at 15psi for break in, full spool by ~3500rpm!
    First autocross 3/29/15
    1st Registered 818 in Connecticut 7/24/2015. 9 months - 1 day from kit pickup!

  37. #37
    Senior Member flynntuna's Avatar
    Join Date
    Apr 2011
    Location
    San Diego Ca 92106
    Posts
    1,972
    Post Thanks / Like
    So, are you saying that switching to "better" pads in the rear, would be equivilant to upgrading to larger disc and caliper in the rear?

  38. #38
    Senior Member xxguitarist's Avatar
    Join Date
    Nov 2013
    Posts
    389
    Post Thanks / Like
    Yes, a pad with more bite will increase braking force on that end of the car. It's vaguely equivalent as far as stopping ability goes.

    The other advantage of larger brake components is heat. Higher end pads also handle heat better, but not to the same degree as larger brakes.
    -Andrew

    Building 818S/R #297 with Tamra
    08 Mazdaspeed3 | '12 F800R | '97 Miata

  39. #39
    Senior Member flynntuna's Avatar
    Join Date
    Apr 2011
    Location
    San Diego Ca 92106
    Posts
    1,972
    Post Thanks / Like
    More food for thought, thanks.

  40. #40
    Senior Member Junty's Avatar
    Join Date
    Dec 2013
    Location
    New Zealand
    Posts
    140
    Post Thanks / Like
    Hey Matteo92065. Rather than decreasing the front - why not try similar to my addition (originally Bob's idea) and put standard WRX 4 pot callipers on the rear? I would also add the same yellow stuff pads - just to keep things similar all around? The DBA rotors ensure that you keep the hub plate and handbrake assembly unchanged. As shown by Bob above - there is a minor hole relocation required to bolt the 4 pots on - but this is an easy mod...

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Stewart Transport

Visit our community sponsor