Subaru 4 pots!

[Wonderbar]

Originally Posted by Admiral Ballsy

The pistons in these are smaller than in the stock calipers. Since the positioning is the same, the net result is reduced braking torque.

But there are 4 smaller opposing pistons instead of two sliders.

[wheelhaus]

Originally Posted by Wonderbar

But there are 4 smaller opposing pistons instead of two sliders.

Correct, the total surface area of the pistons needs to be compared. Same for the rear. If by chance they are overall slightly less powerful, then marginally more foot pressure would be needed to achieve the same pad pressure.

This is rather important because these brakes are coming not only from a different car, but also a different style car, with a different weight balance and CG. So, the fore/aft balance should be considered and measured at the very least. Braking torque can be modified with pad selection, but this method is only consistent if the pads friction levels are consistent front/rear as the pads heat up. If the fronts are too strong, you extend braking distance because the rears are underutilized. If the rears are too strong, you again extend braking distance, but also risk losing the rear end too easily.

[Wonderbar]

Originally Posted by wheelhaus

Correct, the total surface area of the pistons needs to be compared. Same for the rear. If by chance they are overall slightly less powerful, then marginally more foot pressure would be needed to achieve the same pad pressure.

This is rather important because these brakes are coming not only from a different car, but also a different style car, with a different weight balance and CG. So, the fore/aft balance should be considered and measured at the very least. Braking torque can be modified with pad selection, but this method is only consistent if the pads friction levels are consistent front/rear as the pads heat up. If the fronts are too strong, you extend braking distance because the rears are underutilized. If the rears are too strong, you again extend braking distance, but also risk losing the rear end too easily.

Ill do measurement comparisons when I get settled on the east coast in a few weeks.

[Admiral Ballsy]

Originally Posted by wheelhaus

Correct, the total surface area of the pistons needs to be compared.

It doesn't work that way.

Sliding calipers exert the same force as dual opposing pistons of the same size. The stock calipers have 48mm pistons, IIRC, so you'd need four-piston calipers with...48mm pistons to achieve the same clamping force.

There are advantages to opposed-piston calipers conceptually (obviously, or they wouldn't exist), but these particular calipers will exert less force on the discs for a given amount of cylinder stroke.

[Flat Black VW]

Originally Posted by Racecomp Engineering

He doesn't have to because the calipers are not differentially bored, so you can put the bleeder on top without issue.

- andy

So I have the calipers and have them apart for powder coating. When I reassemble them would it be of any benefit to switch the bleeder to the bottom of the caliper? Or does it really not matter?

[nokia7190]

Anyone have subaru 4/2 pots installed would interested in this Girodisc 2 piece brake rotors - GAUGING INTEREST

[Draco-REX]

EDIT: mis-brained.. nevermind.

[Admiral Ballsy]

Again, that's not how it works. It's not "50 units per pad". If the piston pushes with 100 units, the other side of the bracket pushes back with 100 units. If it didn't, the thing would fall off the car.

Opposed pistons are used for several reasons, but force applied isn't one of them (BMW uses only single-piston calipers, BTW), even on M-cars).

You don't have to take my word for it. Google around.

[OrbitalEllipses]

Originally Posted by Flat Black VW

So I have the calipers and have them apart for powder coating. When I reassemble them would it be of any benefit to switch the bleeder to the bottom of the caliper? Or does it really not matter?

It would be easier to swap left to right than reposition the bleeders. You can swap left to right without problems as the pistons are all the same size (not differentially bored). You don't want to do that on Brembos because the pistons are different sizes (differentially bored) and it could cause funky pad wear.

[Wonderbar]

Here's a bunch of borrowed info from multiple sources.

"The reason a multi piston caliper is such an advantage is because a larger clamping force is applied across the disc. This force is also much more evenly distributed and keeps the leaeding and trailing edges of the pad from literally flexing away from the disc as the backing plate distorts under high loads. More pistons make the entire pad able to do more work along with wearing the friction material more evenly.

A step further is a multi piston caliper with different sized pistons. The leading edge of the pad always runs hotter. By making the leading piston a little smaller than the trailing one(s), a more even temperature can be maintained across the entire pad surface as opposed to the leading edge running hot.

A fixed caliper with opposing pistons also tends to not vibrate through the pedal as much since it is not sliding, and both the inner and outer pads do the same amount of work. Ever notice how sliding calipers always wear out the inner pad against the piston first?"


http://www.hayesdiscbrake.com/hayes-u/caliper/
http://auto.howstuffworks.com/auto-p...e-calipers.htm
http://www.brakeandfrontend.com/Arti..._than_one.aspx

[Wonderbar]

Originally Posted by Flat Black VW

So I have the calipers and have them apart for powder coating. When I reassemble them would it be of any benefit to switch the bleeder to the bottom of the caliper? Or does it really not matter?

The bleeders have to be on the top...

Air bubbles bleed via being lighter than the brake fluid...

If you put the bleeders on the bottom you'll drain your fluid and suck or in...

[Draco-REX]

Originally Posted by Admiral Ballsy

Again, that's not how it works. It's not "50 units per pad". If the piston pushes with 100 units, the other side of the bracket pushes back with 100 units. If it didn't, the thing would fall off the car.

Opposed pistons are used for several reasons, but force applied isn't one of them (BMW uses only single-piston calipers, BTW), even on M-cars).

You don't have to take my word for it. Google around.

Ok, I can see where this makes sense. The pressure is applied to both the piston and the housing..


Hmm...

[Wonderbar]

If you read above, the general theory is that the pressure is more evenly distributed across the pad, better heat dissipation, etc... All the things that are required out of a higher performing part like that.

Clamping force isn't the only important thing.

Think of it like penis comparison, it is better to be bigger or to be able to perform a little better for a lot longer.

[Admiral Ballsy]

Originally Posted by Wonderbar

Clamping force isn't the only important thing.

Yep. Neither is number of pistons. Again, look at an M3's brakes sometime.

Bottom line is, the 4/2 setup from the earlier WRX isn't any improvement over the stock. Neither is it significantly worse. Since most people doing it are likely driven by aesthetics (NTTAWRT), no harm no foul.