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Discussion Starter #1
Spent a few hours getting ready to fit my AP Racing front brake set today, and was stunned by the comparison with the stock set.

Now, I am obsessive with weight of the car, so I rumaged round the garage and found an old set of my original brakes. I wanted to check just how much extra weight the AP set were going to cost me. :bawling:

Here you can see the original set next to the new AP's



Now onto the scales


Stock front disc - 280mm


AP Racing front disc - 343mm


Stock 2 piston cast caliper


AP racing 6 piston caliper CP5555


So onto the results:

The stock disc, (now this is a cr4ppy 280mm, 28mm thick item) weighs in at 7.0kg's.

The AP racing disc 343mm, 32mm strap drive is 7.5kg's (thanks to ally bell, and thinner wall section)

Stock caliper, including worn pads = 4.5kg's

AP Racing caliper with new pads and ally mounts 4.0kg's (comparable with the stocker)

The absolutely unbelievable result, is that the bigger, better, badder AP set is exactly the same weight per side as the crappy stock set.

How happy am I?????:clap: A totally unexpected surprise



Now, just to clarify, the stock brakes are not from a GTR, they are cast iron twin piston calipers found on lesser Skylines, so probably heavier than the GTR 4 Pot Brembo, but I would expect the GTR disc to weigh considerably more than the skinny 280mm GTS one.

Perhaps someone could post up the weights of the stock brakes for R32, R33, R34, etc.

Oh, and to put my weight phobia into perspective, I opted for the 343mm AP kit, even though the bigger 356(???) R34 kit is the same price. This was due to the bigger disc weighing 1.5kg's a side more. (the friendly AP chap told me the weight difference). I also figured as my car now weighs just over 1 ton, I wouldn't really need the bigger disc version.

The whole exercise today just shows why serious racing teams still use AP racing, rather than the bling bling products seen on many dressed up road cars.:p
 

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Wow, that is suprising. And those APs make your OE disks look really sad!
 

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Discussion Starter #3
Ha ha, yes that old set is sad. Looks like they have been lying at the bottom of the ocean.
 

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very good, i was supprised the A.P's was lighter giving there size.

However, do A.P match the calliper to the car? For instance, your master cylinder will only push XXX amount of fluid to work the calliper. So the insides of the calliper need to be matched to the master cylinder to give the same breaking force. (more so from front to rear when not changing both)

Alot of people say that the new break kit works better but this is normally down to the calliper being new and running a better pad over previous set up.

I know that there is one company that build there callipers to match the master cylinder on the vehicle, is this the same for A.P?
 

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Discussion Starter #5
Erm, don't know, but I do know that most brake master cylinders are either 3/4 inch or 1 inch in diameter. Nissan use 3/4, so should give same feel as any aftermarket racing set up.

I have a 4 pot set to go on the rears, and for now I have fitted a Tilton brake bias adjuster on the rear line. Once the new cage is in, I will be converting to a Tilton brake pedal set, with double cylinders and brake bias bar.

Will post up on how they feel, or any problems on the bias side.
 

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what matty was getting at is that your master cylinder will displace XX amount of fluid through full travel. If the internal volume of your pistons x travel x 4 exceeds this, you won't be able to get full piston travel at the calipers. (ignoring the whole front/rear bias thing!)

Not normally an issue, given teh original volume of the caliper doesn't count, only the amount of fluid required to move the pistons. However, what you may notice is that as you now have 6 piston fronts, with potentially a greater swept volume than the stock calipers, Y amount of pedal travel will translate into less piston (& therefore pad) travel. Or in English, you'll need to push the pedal more for the same amount of brake "pressure" - however, your more efficient braking system may couteract this from a "feel" perspective.

It's all a bit complicated and you should at least work out the "swept" volume of your new calipers vs the old ones to see if it's significantly greater.
 

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Discussion Starter #7
Ah I see. It is a set designed for the GTR, and my car has same master cylinder, so should be 'all good'.

But to further what your saying, how about some quick maths then (engineer in me reacheds for vernier and calculator, mwah ha ha)

Stock unit has 2x40mm pistons = 25.132 cm^2

AP unit has 40mm, 33mm, 28mm pistons = 12,566+8.553+6.158 = 27.277 cm^2

Stock unit moves both pads, but AP has 2 sets of pistons, so I would assume the travel cancels each other out??? i.e. the 2x40mm pistons have to move the pad 2x the distance that each bank of AP piston has to.

Stock Master cylinder is 1.98 cm^2

So stock has a 12.7:1 ratio versus 13.8:1 of the AP set.

If we were to say that full movement is 2mm of pad travel, the stock system would require 25.4mm master cylinder movement, as opposed to 27.6mm on the AP set. Who knows what the pedal to MC ratio is????, but it doesn't add up to a great deal of difference.

The other factor is that the piston sizes on the AP are not the same, so presumably for a small pedal movement you would get a greater movement on the AP small pistons, then progressively the power of the bigger pistons as you push harder on the pedal????

The AP having a much broader range of progression (and therefore feel) due to the differential piston sizes.
 

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Ah I see. It is a set designed for the GTR, and my car has same master cylinder, so should be 'all good'.

But to further what your saying, how about some quick maths then (engineer in me reacheds for vernier and calculator, mwah ha ha)

Stock unit has 2x40mm pistons = 25.132 cm^2

AP unit has 40mm, 33mm, 28mm pistons = 12,566+8.553+6.158 = 27.277 cm^2

Stock unit moves both pads, but AP has 2 sets of pistons, so I would assume the travel cancels each other out??? i.e. the 2x40mm pistons have to move the pad 2x the distance that each bank of AP piston has to.

Stock Master cylinder is 1.98 cm^2

So stock has a 12.7:1 ratio versus 13.8:1 of the AP set.

If we were to say that full movement is 2mm of pad travel, the stock system would require 25.4mm master cylinder movement, as opposed to 27.6mm on the AP set. Who knows what the pedal to MC ratio is????, but it doesn't add up to a great deal of difference.

The other factor is that the piston sizes on the AP are not the same, so presumably for a small pedal movement you would get a greater movement on the AP small pistons, then progressively the power of the bigger pistons as you push harder on the pedal????

The AP having a much broader range of progression (and therefore feel) due to the differential piston sizes.
When you're working out ratios you need to consider the total piston area.33

If your stock callipers have 2 x 40mm pistons and the new set has 2 x 40mm, 2 x 33mm and 2 x 28mm then the master cylinder will have to push a lot more fluid to get the same result.

Master cylinder ratios for sliding pin callipers are indeed different than opposed callipers. I seem to remember 25:1 being talked about for opposed and 15:1 for sliding pin. However these figures are for bikes so I have no idea how they translate into cars systems with front/rear ratios and boosters.

Also worth bearing in mind the different master cylinders on different GTRs. I'm sure it's been posted before but I think that there are three different units. I assume that your set-up if it is the same as the GTR is the same as the R32 GTR ABS unit. Would mean that the R33 unit could be a useful upgrade if your pedal travel is too long.
 

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The other factor is that the piston sizes on the AP are not the same, so presumably for a small pedal movement you would get a greater movement on the AP small pistons, then progressively the power of the bigger pistons as you push harder on the pedal????
Differential piston sizes are to spread the force (pushing the pad) across the disk better. Equally sized pistons would end up wearing the leading edge of the pad more.
 

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Discussion Starter #10
When you're working out ratios you need to consider the total piston area.33

If your stock callipers have 2 x 40mm pistons and the new set has 2 x 40mm, 2 x 33mm and 2 x 28mm then the master cylinder will have to push a lot more fluid to get the same result.

Master cylinder ratios for sliding pin callipers are indeed different than opposed callipers. I seem to remember 25:1 being talked about for opposed and 15:1 for sliding pin. However these figures are for bikes so I have no idea how they translate into cars systems with front/rear ratios and boosters.
I was taking into account that an opposed piston arrangement (like AP) only moves the pads half the distance of a single sided piston, as the single sided device has to move both the nearside pad, as well as the frame to press on the far side pad, so twice the distance, or piston travel. The overall piston movement must surely be the same as if it was split between two sides?

Thanks for highlighting options on different MC's:thumbsup: Although my aim is to fit a motorsport pedal box, which will have separate front rear MC's and balance bar arrangement. That will allow the correct adjustment, pedal travels, etc.
I can't fit one now as I can't reach the gear lever with the seat in it's eventual position, lol

Saving for that sequential gearbox.
 

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where did you get the ap brake kit from ?
do you have a kit part number ...what skyline are you fitting them to ? i need for 32gtr
and what it the rough cost of the kit ?

cheers
 

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I was taking into account that an opposed piston arrangement (like AP) only moves the pads half the distance of a single sided piston, as the single sided device has to move both the nearside pad, as well as the frame to press on the far side pad, so twice the distance, or piston travel. The overall piston movement must surely be the same as if it was split between two sides?

Thanks for highlighting options on different MC's:thumbsup: Although my aim is to fit a motorsport pedal box, which will have separate front rear MC's and balance bar arrangement. That will allow the correct adjustment, pedal travels, etc.
I can't fit one now as I can't reach the gear lever with the seat in it's eventual position, lol

Saving for that sequential gearbox.
It's apples and oranges to some degree. The single side pistons will move twice as far for a given level of effort as opposed pistons. Assuming that the centring action on the sliding caliper leaves equal clearance either side (they usually don't) and that clearance is the same for an opposed caliper then the sliding caliper's piston (pad) will strike the rotor before the opposed unit does; in this example twice as fast. Then the situation you're describing with the sliding caliper 'evening out' occurs.

On bikes different ratios are quoted for opposed / non-opposed as ideal. They aren't twice as high for opposed unit, I believe for the above reason. However bikes are much more sensitive to these sort of things than cars especially with all the extra fluff that cars use. My guess is that you'll find the pedal travel longer with the APs. Assuming that your MC is the R32 GTR MC I think that the travel is too long already (in my car) bigger piston area will only make that worse. I'm thinking that the R33 MC might be the answer through I'm a little concerned that it's bias is different.

Of course you also have bigger (and better) discs so the mechanical advantage on the disc is greater. Could be that this will offset some of the ratio loss. As long as you aren't precious about bleeding the brakes and fluid costs it's probably best to suck it and see.

I look forward to your findings!
 

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As the kits are car specific, I'm sure all the calculations would have been taken in to account and work as stock but with greater braking force, thats my theory anyway.
 

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Discussion Starter #17
^^^ Thanks :)

where did you get the ap brake kit from ?
do you have a kit part number ...what skyline are you fitting them to ? i need for 32gtr
and what it the rough cost of the kit ?

cheers
Part Number is CP5555 T1000 For Skyline GTR. This set has the 343mm Discs, but there is a 355mm option for same price, and perhaps even the same part no.

Think they were around £1500 +vat, bought from Apex performance.
 
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