[GytRDunKat]

Yeah, I can't say for sure if it was an upgrade, as my master cylinder was shot. Now, it looks cool, and my brakes work. So, in my case, it was an upgrade, if only because they work now

[Tmod]

I will look and see what I can see when I get home tonight but I am not going to take it off the bar. If it is not visable while on the bike you are out of luck sorry. They are not nissan calipers on the busa so it shouldn't be a nissan master, but I will look.

Don't need to take anything off, It is right on the outside of the casting.

A smaller piston will increase the stroke length when applying the brake but will deliver more pressure to the caliper, The more pressure the more braking power.

A larger piston will decrease the stroke length when applying the brake but deliver less pressure to the calipers which equals less braking power.

If memory serves correct when I sent a M/C to Sprague his pre was a 5/8" bore, The post kats are a 14mm bore so a post M/C would apply more pressure to the calipers increasing braking power.

Tmod

[squiggy]

A smaller piston will increase the stroke length when applying the brake but will deliver more pressure to the caliper, The more pressure the more braking power.

Even though it's moving (compressing) less volume?

[Tmod]

Even though it's moving (compressing) less volume?

Yes as there is still a area that the caliper pistons move out so the pad engages the rotor, The smaller the M/C piston the less fluid it displaces for a given amount of travel.

Tmod

[scottynoface]

I will look and see what I can see when I get home tonight but I am not going to take it off the bar. If it is not visable while on the bike you are out of luck sorry. They are not nissan calipers on the busa so it shouldn't be a nissan master, but I will look.

The master does not need to match the calipers. Ninjas have come with Nissin M/C for years (at least since 2000) and had crappy Tokico calipers until 2007.

[squiggy]

Yes as there is still a area that the caliper pistons move out so the pad engages the rotor, The smaller the M/C piston the less fluid it displaces for a given amount of travel.

Tmod

ahhh.

The master does not need to match the calipers. Ninjas have come with Nissin M/C for years (at least since 2000) and had crappy Tokico calipers until 2007.

I bought on ebay last week a Nissin 4-piston brake caliper cheaply just to see if it will mate to the Post Kat fork. The post Kat's have a narrow bolt spacing to them.

[squiggy]

Well the bolt spacing on the Nissan caliper did not match the Katana fork. At least it was only $5.00 I spent.

[tone]

A smaller piston will increase the stroke length when applying the brake but will deliver more pressure to the caliper, The more pressure the more braking power.

A larger piston will decrease the stroke length when applying the brake but deliver less pressure to the calipers which equals less braking power.
Tmod

Not quite right there mate piston size has no effect on the stroke at the cylinder & very little effect at the caliper all it effects is the volume of fluid moved, the more area at the caliper pistons the more fluid you need to move as the pistons go out for the same effect

A fully charged & properly bled hydrolic brake system is in effect a solid rod the force applied at one end is equal to the force applied at the other
Discounting stroke at the master cylinder for now different piston diameters are simply to move varying amounts of fluid & keep the area behind the caliper pistons full & the master cylinder with enough fluid in it to keep the holes covered

tone

[Tmod]

Not quite right there mate piston size has no effect on the stroke at the cylinder & very little effect at the caliper all it effects is the volume of fluid moved, the more area at the caliper pistons the more fluid you need to move as the pistons go out for the same effect

tone

I disagree with you on this one, You mention fluid moved and the piston diameter at the master cylinder is what controls that fluid movement. You also state that the more area at the calipers the more fluid required to move them a given distance, So being that a smaller piston moves less volume you would need to pull the lever further until the pad puts force on the rotor.

Tmod

[mreedohio]

definitive answer on the markings on the busa m/c. its 5/8. this thread had me curious so i went out and pulled mine off the bars.

[tone]

Discounting stroke at the master cylinder for now different piston diameters are simply to move varying amounts of fluid & keep the area behind the caliper pistons full & the master cylinder with enough fluid in it to keep the holes covered
tone

Tmod
you missed this bit when you quoted me mate
The point i was making is that diameter combined with stroke controls the amount of fluid moved

Eg a smaller diameter piston with a longer stroke will move as much fluid as a larger piston with a shorter stroke

simples

[loudnlow7484]

Eh, and a 3" long wrench moved by 1" will move as much as a 9" long wrench moved 3"...... that's why it's called leverage.

This article is from Popular Hot Rodding (a car mag), but the principals are the same-

http://www.popularhotrodding.com/tech/0601phr_braking_systems/index.html

The most critical factor in master cylinder selection is bore size. Bore sizes can range from 5/8 inches upward to 1 1/8 inches or more. The bore size determines the amount of hydraulic pressure and fluid volume that will be sent downstream to the calipers. The actual amount of hydraulic pressure generated is based on the amount of force coming from the pedal or booster being divided by the area in square inches of the master cylinder bore. For example, a master cylinder with a 1-inch bore has .785 square inches or bore area. ( Bore x Bore x .785) If the pedal or booster delivers 500 pounds of force to the master cylinder, the hydraulic pressure will be equal to 500 divided by .785, which would result in 637 psi going to the lines. The displaced volume capacity is then based on the length of the available stroke multiplied by the bore area. It's the same formula that's used to calculate engine displacement for one cylinder.
Generally speaking, if the master cylinder bore is too large, the driver will feel a very hard pedal feel with minimal pedal travel, and will have a difficult time generating the necessary pressure to effectively operate the brake system. If the master cylinder bore size is too small, the driver will be able to generate a lot of pressure, but the pedal may have an excessively long stroke or a very spongy feel. And if the bore size is way too small, the pedal or master cylinder may bottom out before enough volume is pumped to operate the calipers. The best advice would be to consult with the manufacturer of the brake system you will be using and work with them to pick the right size for your application.

[scottynoface]

Generally speaking, if the master cylinder bore is too large, the driver will feel a very hard pedal feel with minimal pedal travel, and will have a difficult time generating the necessary pressure to effectively operate the brake system.

VW Jetta ftw!

[Tmod]

Tmod
you missed this bit when you quoted me mate
The point i was making is that diameter combined with stroke controls the amount of fluid moved

Eg a smaller diameter piston with a longer stroke will move as much fluid as a larger piston with a shorter stroke

simples

Now you have me confused you said that I wasn't quite right in your reply yet now you state that a smaller diameter piston does not move the same fluid as a larger piston using the same stroke. if you read my post I said that the smaller diameter piston increases the stroke needed compared to a larger diameter piston to push the pads out the same distance.

Tmod

EDIT: Something I dug up while cruising the net.

Master Cylinder Sizing: This is where many people stray from reality when explaining master cylinders. An OE master cylinder is sized to be able to have enough fluid capacity for the combined total caliper piston volume consumed at maximum ‘calculated’ running clearance (the gap between the pads and the rotors - usually less than 1mm). Its not the total piston volume as that would be huge, but the following simple equation [pad gap * piston area of all pistons in circuit]. Most caliper piston diameters are in the 30mm range while most m/c’s are on the 13-20mm range.

OE m/c’s are sized to give the rider the best blend of lever force and travel characteristics. Since the m/c’s purpose is to translate a lever force into fluid pressure (force per unit area = psi), the bore diameter determines how the lever feels. To understand the impact of bore diameter, think of the equation force/area with the force being lever force and the area being the area of the m/c bore. To display the math a little, I’ll use nice round numbers. Say you can generate 1000lbs of force and have a 1 in2 m/c bore area. That equals 1000lbs/1 in2 or 1000psi. By increasing the m/c bore area to 1.25 in2, using the same equation, you can only generate 800 psi. Likewise, by decreasing the m/c bore area to 0.75 in2 you generate 1333 psi.

M/C bore area summary: The bigger the area of the bore, the less pressure is generated for a given input lever force. The smaller the bore area, the more pressure can be generated from that same input force

Lever stroke is also impacted by m/c bore area. The total volume of fluid generated in the m/c is the equation [m/c bore area * m/c piston travel]. Again, using the 1 in2 m/c bore area from above and keeping the m/c piston travel constant at 0.5 in, the original case 0.5 in3of fluid volume. Increase the bore area to 1.25 in2 = 0.625 in3. Likewise, decreasing the m/c bore area to 0.75 in2 = 0.375 in3.

M/C volume summary: The bigger the area of the bore, the less stroke required to move a given volume. The smaller the bore area, the more stroke is required to move that same volume.

Combining the two summaries is the key to understanding master cylinder sizing:

The bigger the bore, less stroke but more force will be required to reach a given pressure. The smaller the bore, more stroke but less force will be required to reach that same given pressure.

The balance between force and stroke is what the tuners at the OE call “feel”. From my experience, I have seen smaller m/c’s on OE machines which leads me to believe that the goal is to give a system with less effort and more stroke than the other way around. Many stock units are around 13mm in diameter.

NOTE: A common misconception is that the bigger bore m/c’s make the brakes stiffer. They do not. The increase in required force and more importantly shorter lever stroke is mistakenly called increased stiffness because the brakes engage sooner.

[ctandc]

Check this thread

http://katriders.com/vb/showthread.php?t=102572&highlight=master&page=2