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Old 02-16-2010, 07:01 PM   #1
Zaider
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Default Difference between RS and STI Master Cylinders?

Hey All,

I tried searching but couldn't find anything.

Is there a difference between an RS Brake Master Cylinder/Clutch Master Cylinder and that of an STI?

Im currently half-way through a V7 STI swap into my bugeye 2.5RS and realized that i dont want to go through rerunning the lines for the two master cylinders and the brake booster.

Should I be swapping them? If so, would any STI MC's and brake booster work?

Thanks in Advance,

Z
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Old 02-16-2010, 08:25 PM   #2
FuJi K
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The difference is the piston diameter. It's 1/16" bigger than yours. The fittings on the master cylinder are probably gonna be in a different spot on the STi MS.

I run a SVX FWD non-ABS 1 1/16" MS on my '99 Impreza L Sport Wagon.
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Old 02-17-2010, 12:21 PM   #3
Zaider
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So, my understanding is that technically, I could use my stock master cylinders but Im going to have to use more force on the brake pedal for the same amount of brake force, and the same with the clutch. Is that correct?

Thanks!
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Old 02-17-2010, 01:11 PM   #4
FuJi K
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not that much force needed. I ran my 15/16" MS with the Brembo brakes. I was getting an inconsistent brake pedal stroke with driving at a performance level and I replaced mine with the SVX one. It didn't fix it so I figured the LOW pad and all was the issue. I'm still trying to figure it out this spring. I'm still on my single brake booster. The MS change did firm up the pedal, but didn't fix the inconsistency.

Your 2.5RS and all ABS Imprezas (non-STi) runs the 1" MS. The Outbacks from 97+ run a 1 1/16". You shouldn't have any issues at all. WRX run the same size as yours. I'm not sure on the '08+ though.
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Old 02-18-2010, 01:13 AM   #5
Zaider
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Wow. Thanks very much for all the help. I've found a cheap STI BMC and CMC so ill swap those over. Is there any difference between the brake boosters (RS to STI?)
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Old 02-18-2010, 04:10 PM   #6
FuJi K
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I'm unsure on the boosters. They seem to all run the dual stage boosters. The pedal on the STi is somewhat firm, but not like mine because of the single vs dual booster. Single boosters give firmer pedal. I want to ditch the booster all together.

What are you looking to achieve with the booster? Don't jsut get it because it's STi. I run a 2.5RS clutch MS with my 6spd setup. The STi isn't faster in anyway. You should run the parts based on what you using them for, not because of the "STi" name.
You see the only thing STi that I am running is the JDM 6spd DCCD tranny. Well I'm also running a '07 STi intake manifold with throttle body but that's because I needed one and I happen to get a good deal on the upper mani with TB ($180). I have WRX heads and Legacy block (EJ22T).
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Old 02-18-2010, 05:04 PM   #7
Zaider
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To be honest, Im not really sure and was probably going to do it simply because it was STI and the rest of my car is getting converted over to STI parts (ej207, JDM V7 non-DCCD 6spd, brembos). I figured that since the engine bay is completely empty right now, I should swap in whatever I could while its easy.

It wasn't necessarily "faster" that I was looking for, more pedal feel. This is simply a daily driver swap. It will rarely see the track except for the odd autocross when I feel like showing up and possibly a gravel or snow TSD if I feel like risking my car.

Im unsure what you mean when you say "They seem to all run the dual stage boosters". Do you mean all STI's or all GD Imprezas?
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Old 02-18-2010, 05:41 PM   #8
FuJi K
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All ABS equipped Subarus run a dual stage. I dunno if there's a 3 stg.. haha Oly the non-ABS Subarus ran the single stg.

....Stages... that's just what I hear. I can see the difference in the boosters. Single stg boosters are not as thick. Dual stage looks to have a second part to it and is thicker.
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