has anyone installed Rx7 brakes?

[andyhorror]

jonc. i intend to go rear disc also more for ease of maintenance than anything. this setup would be topped off with a 1in master and adjustable prop valve. i have learned much by reading the stickies on this forum repetitively haha.

[SleeperZ]

Horsepower is for accelerating, brakes are for decelerating.  There is no horsepower rating for a brake system, it makes no sense.

 

It makes sense because weight and hp equals kinetic energy which must be dissipated in the brakes. The more power you have, the more speed you must drop to make the turn (or stop).

[NewZed]

All that matters is how you plan to use the brakes.  Tying brakes to horsepower is based on an assumption that the horsepower will be used to go faster.  But stopping a 120 HP car from 100 mph requires dissipating the same amount of energy as stopping a 1,000 HP car from 100 mph.  Assuming the same weight.  It's just bad logic to tie them together.  A lot of these threads get side-tracked from illogical thinking.

[helghast7]

All I was trying to do was give as much information on the calipers in question as possible. I gave the weight of the car in question and the average power levels of said car the factory brake system can handle before said car requires larger brakes. Being as how our cars and the FD are similar in weight both of these could be of use to someone that knows what to do with the data.

 

And power levels do matter for brake systems in pretty much any form of racing, a 120hp car can only make it to 80mph before needing to brake to enter turn A where a car with 300hp can make it to 110mph before needing to brake to enter the same turn which puts more load on the brakes and tires causing them to fade and overheat.

 

It's a piece of information I'd like to know before changing brakes. Though I'm sure most people just stick to factory because its safe and simple and the rest just go to whats shinny.

Edited November 13, 2014 by helghast7

[NewZed]

I almost mentioned weight as a good piece of information.  The thread in general though illustrates how easy it is to get unfocused.  The OP only started it because "when i picked up one of the calipers. WOW are they light. all aluminum four piston fixed caliper and they're cheap at 35 a piece.

so i was wondering if this would be another budget upgrade option."

 

Budget "upgrade" and racing applications are two different worlds.  I was just trying to redirect back to the basics of brakes.

 

Edit - not that I'm an expert.  I've been surprised though that nobody mentions one benefit of switching to disc in the back - no more up and down brake pedal adjustment with the parking brake handle.  Waiting for the star wheel to hit the next notch.

Edited November 13, 2014 by NewZed

[johnc]

And power levels do matter for brake systems in pretty much any form of racing, a 120hp car can only make it to 80mph before needing to brake to enter turn A where a car with 300hp can make it to 110mph before needing to brake to enter the same turn which puts more load on the brakes and tires causing them to fade and overheat.

 

 

Its not the horsepower, its the vehicle weight and speed at the end of the straight plus mid corner speed that matters as far as braking is concerned.  Its common on a road race track for a lower horsepower car to have a higher speed at the end of the straight and the end of the braking zone due to much better handling and lighter weight.

[helghast7]

This is getting far off topic, but you with your theory a miata should always beat a corvette and a gtr in a road race.

[johnc]

I've seen it happen and "always" is never true in road racing.  The winner of the race is the one that crosses the finish line first, not the one with the most horsepower.  My 325hp 240Z beat every Viper, every Z06 Corvette, every Mitsubishi Evo, every Porsche 911 at the 2003 and 2004 OTC. 

 

Compare lap records at various race tracks and you'll see that many low horsepower cars can lap at equal or better times then higher horsepower cars.  When I raced Spec Racer Fords we had all of 110hp yet our lap times at WSIR (arguably a horsepower track) were equal to race cars having double or triple the horsepower we had.  A Formula Atlantic with 240hp will absolutely destroy ANY Corvette or GTR on any road race track in the country.

[andyhorror]

i think that ill give the rx7 calipers a go with the 300zx rotors and link my build thread back here when i make it that far.

[Miles]

jonc. i intend to go rear disc also more for ease of maintenance than anything. this setup would be topped off with a 1in master and adjustable prop valve. i have learned much by reading the stickies on this forum repetitively haha.

 

You may want to research brake balance issues in the brake section before deciding to install rear disk brakes.  There are some good threads with balance calculations that quantify balance issues  associated with various front and rear disk combinations.  You will need to know the piston and rotor diameters for each caliper you plan on using. Match what you are planning to use to the balance calculations HybridZ members have posted or you can calculate based on your planned set up.  Many of the so called upgraded front and rear disk combinations  result in too much front bias.

 

If you do the rear disk swap be aware that worn bearings and warped stub axle flanges can cause the pads to drag.

[helghast7]

I've seen it happen and "always" is never true in road racing.  The winner of the race is the one that crosses the finish line first, not the one with the most horsepower.  My 325hp 240Z beat every Viper, every Z06 Corvette, every Mitsubishi Evo, every Porsche 911 at the 2003 and 2004 OTC. 

 

Compare lap records at various race tracks and you'll see that many low horsepower cars can lap at equal or better times then higher horsepower cars.  When I raced Spec Racer Fords we had all of 110hp yet our lap times at WSIR (arguably a horsepower track) were equal to race cars having double or triple the horsepower we had.  A Formula Atlantic with 240hp will absolutely destroy ANY Corvette or GTR on any road race track in the country.

 John you're absolutely correct. Its all about power to weight ratio. My original intention was to merely state that the vehicle in questions front brakes can handle the stopping energy needed at the vehicles weight range at an estimated acceleration and power range before said vehicle required upgraded brakes.

 

And I only stated such estimate because I assumed that people with the knowledge and ability to understand such data could use it to their advantage so that they wouldn't wade into uncharted territory only to find it inadequate for their use.

 

I suppose the saying still stands correct about assuming judging by the response.

[Sideways]

yes socorob they are smaller but four equal out to more surface area than 1 big piston. just like 4 valves be betta than two

But as far as clamping force is concerned you dont count four pistons, you count two.  You count the pistons on one side of the caliper, not both, as the braking pressure it being split/halved between the two banks. For example, a caliper made of just two of these pistons (one one side of the caliper), will have the same clamping force as 4 of these pistons in 2 banks. 

 

Being a rolla guy myself, Its actually a peeve of mine how popular rx7 brakes are for the rolla community.  For 99% of people out there, they are not an upgrade (on the rolla).  They see "oo 4 pistons!" and conclude 4 pistons is better than one!" "Moar braking force!" and the like.  When in actuality, you need to be counting the surface area of 2 of the pistons, not 4, and the surface area of 2 of thoe pistons is < one corolla piston.  They actually have *less* braking force than the stock single piston for the rollas, and in fact most of the people who do these "upgrades" start having issues with the rears locking up before the fronts (And they still conclude they have more front force, it baffles me).  The only advantage to these brakes for the rolla is that they run larger rotors, so they can absorb/deal with more heat.  But seriously, unless youre making a LOT of power over stock with the rolla, the factory system in good condition can see 20-30+ minutes on the track without any brake fade (on heavy brake demanding tracks to boot such as SoW and the like).  All these guys are doing is adding unsprung weight for braking benefits (endurance) they will never see, because they dont get enough heat in their brakes to over cook the stock setup, while throwing off their braking balance at the same time.

 

But I digress.  What is the surface area of the stock z piston? what is the surface area of two of these rx7 pistons? Thatll tell you which will have more clamping force.  The next area of concern will be the potential advantages of a vented rotor vs the non vented rotor. But what are you using the car for? Do you make a sizable amount of power over the factory setup?  Are you doing long extended track sessions?  Just an autocross toy? Weekend warrior?  If youre not over heating the stock pads/rotors, you will see *no* benefit here, and, much like the rolla guys, you will actually be hurting your performance- not helping it, as youre adding unsprung weight to your car. 

[socorob]

http://www.jakelatham.com/radical/info/brake_calculators.shtml

[andyhorror]

But as far as clamping force is concerned you dont count four pistons, you count two.  You count the pistons on one side of the caliper, not both, as the braking pressure it being split/halved between the two banks. For example, a caliper made of just two of these pistons (one one side of the caliper), will have the same clamping force as 4 of these pistons in 2 banks. 

this is actually opposite from everything that I've just read. you count all of the pistons in a fixed caliper system when calculating your piston surface area, but double them when figuring area on a floating caliper setup. 

 

http://www.rallydesign.co.uk/pdf/designing_4_pot_brakes.pdf

 

piston area calculator along with some other good info on the site

http://brakepower.com/help_abc_27_PAC_t.htm 

 

rx7 piston surface area for both front in millimeters based on rough 30mm measurement - 5652mm

240z pisotn surface area for both front in mm based on rough 55mm measurement - 9498mm

 

does this seem right?

have i completely screwed something somewhere?

how is a more modern sports car that seems to be a good bit heavier running halved brakes?

Edited November 17, 2014 by andyhorror

[G-E]

You are correct, you measure each piston on a fixed caliper, and double it for a floating caliper.

 

But comparing how the calipers work on different cars won't tell you the story, the leverage of the pedal, the size of the pads, the size and stroke of the master cylinder, any traction control devices like ABS, etc, all affect the outcome...

 

That all changes once they are on the same car, then you can do a direct comparison with the hardware you've got, and the only variation should be the pad area.

[Sideways]

this is actually opposite from everything that I've just read. you count all of the pistons in a fixed caliper system when calculating your piston surface area, but double them when figuring area on a floating caliper setup. 

 

http://www.rallydesign.co.uk/pdf/designing_4_pot_brakes.pdf

 

piston area calculator along with some other good info on the site

http://brakepower.com/help_abc_27_PAC_t.htm 

 

rx7 piston surface area for both front in millimeters based on rough 30mm measurement - 5652mm

240z pisotn surface area for both front in mm based on rough 55mm measurement - 9498mm

 

does this seem right?

have i completely screwed something somewhere?

how is a more modern sports car that seems to be a good bit heavier running halved brakes?

Im failing to see the discrepancy? I was talking about clamping force.  Please note: Actual piston surface area =/= clamping force.  That was kind of my point.

 

Please refer again to my example again, 2 calipers- Caliper A has 4 pistons of the same size, 2 on each side (a fixed caliper), caliper B has 2 pistons of the same size, all on one side (a floater).  I said these would have the same braking force.  Lets elaborate on this however and lets plug some numbers in. Assume each of these pistons in these calipers have 1" of surface area, then well use the formula you cited.  Caliper A has 4 1" pistons, for a total of 4" of surface area.  Caliper B has 2", but gets doubled.  Giving us a proverbial 4" of surface area to influence the clamping force. Ie, the same. So as long as these calipers had all other factors being the same (Rotor size and distance from its center, types of pads, line pressure going into the caliper, etc and etc), clamping/braking force would basically be the same.

Edited November 18, 2014 by Sideways

[johnc]

There are two separate but related issues - clamping force and hydraulics.  When calculating the hydraulics you you need to count the surface area of all the pistons (caliper and MC) in the system.  For clamping force you just need the hydraulic pressure number and the surface area of the pad.

[Miles]

Brake bias calculator:   http://www.tceperformanceproducts.com/bias-calculator/

[BrakePower]

There are two separate but related issues - clamping force and hydraulics.  When calculating the hydraulics you you need to count the surface area of all the pistons (caliper and MC) in the system.  For clamping force you just need the hydraulic pressure number and the surface area of the pad.

 

First I would like to say that many of the bloggers here seem to know quite a lot about brakes. But more importantly, you all show a lot of interest in the subject. If possible, I would like to add two cents as well.

 

Clamping force is the product of piston area and hydraulic pressure. That’s all. It’s a number that can be used to calculate torque. Even a rather small clamping force can still produce high torque numbers when the effective radius (distance from rotor-center to halfway the swept area of the rotor) is big enough and/or friction coefficient between pad and rotor is high enough.

 

Hydraulic pressure = force on pedal pad times pedal ratio divided by M/C area (single and tandem M/C). For dual M/C: divide force on pedal pad by two (balance bar exactly 50/50).

 

Pad dimensions are not related to clamping force or even brake torque. However, they are related to pad life and pad temperature. A larger pad lasts longer, everything else being equal.

 

About brake bias: assuming we are talking about race cars, I see too much emphasis on bias resulting from hydraulic pressure without taking into consideration under which circumstances this bias will allow all four wheels to lock up simultaneously. Without that information, brake bias calculations are ... “less useful”.

 

The bias number that really matters, is the number that allows for Maximum Possible Deceleration for a given surface condition (friction coefficient between tire and track). Maximum Possible Deceleration occurs when all four wheels are starting to lock up simultaneously after all weight transfer has taken place.

 

The calculator on Brakepower.com gives you a brake bias number based on physical properties of your car. It determines your cars Maximum Possible Deceleration, and matching bias.

 

Hope this helps.

Edited November 22, 2014 by BrakePower

[G-E]

Yes and as you allude to it, the ideal brake bias for one road condition might be wrong for any other condition.

 

So either you need to have an adjuster knob, then get a feel for the road before doing anything silly, and then fine tuning it until you're happy...

 

OR

 

You need a balance that's "good" in most conditions for your driving style, which doesn't really exist unless weather is fairly constant where you are...

 

I know a lot of people that love the way a car feels with overpowered front brakes, because it's a deceiving feeling in the dry, in a straight line -- their opinions might totally change if they were trail braking on a damp surface in a medium corner.