1G RX7 brake calipers fix 90 AWD?

[VETTE_50_TH]

Bigger brakes allow you run shittier pads and rotors and still stop better so... Not that i am going to run cheap autozone rotors and duralast pads on my Evo calipers but you could.

 

[PieEyedPiper]

So you two are telling me I should notice a difference or 9 lbs of unsprung weight?

No, 9lbs would be incredibly hard to detect. 18lbs, however, combined with other weight saving techniques might be detected.

When switching to my SPC upper A-arms I noticed a difference in how the car reacts since the arms are more than double the weight (still not a lot though). Not apple to apples since that isn't unsprung. At least I wouldn't consider it to be.

I also tried on a set of rx7 wheels @14lbs and compared to my stock GSX wheels ( 25-27lbs I think?) I noticed a significant increase in driveability. I actually enjoyed leaving from a stop for once.

If I can feel a positive difference with ~44lbs of unsprung weight removed why would I think that removing an additional 18lbs for a combined ~62lbs would be insignificant? I would imagine it isn't a linear scale and that the benefits become more and more noticeable.

Anyways, this whole topic is purely subjective. No one can reasonably say to another that their wrong or an increase/decrease in unsprung weight will make no difference. Every person's body is different and so is their car.

Honestly though, I have no interest in rx7 calipers. Interesting discussion though.

EDIT: aahh! ninja edit strikes! I think we both know where we're coming from.

 

[Todd TCE]

Being the weight conscience fanatic I am....I'll agree that a few pounds won't make a huge difference.

But...what's missing here is that 'hopefully' the same logic is being applied to everything. I shaved about 25lbs off the race car over a few years. Woo-hoo....25lbs huh? Yea, off a car that weighs about 1500lbs and a car that was lightly built to begin with. And today I don't stop doing it.

Weight is everywhere. When you can shed it; do it. The problem is often cost. When I did a lot of open wheel race prep a guy would ask for a Tilton clutch kit, or a drilled ring gear, or an annular slave cylinder, or two piece rotors etc.etc. What was the weight savings? Often measured in ounces. Some of it rotating, some not. I could shave 15lbs off a FF if you were willing to pay for it. Here's the rub; once you do the simple stuff it gets costly. As a rule of thumb; $100per pound is not out of the question.

Take the easy stuff and keep after it.

 

[ACM]

I switched from 245/45.16 Hoosiers at 20 lbs each wrapped around 8.5.x16 Koseis at ~16lbs each to 285/30.18 Hoosiers at ~24 lbs and 10.5x18 CCWs at ~25lbs.

Not surprisingly, the difference was night and day. Think the difference between an OEM 25lb flywheel and a Fidanza 8lb flywheel is obvious - much more so. What really hurt is that all the CCW weight is in the rim shells, as far out as possible; that rotating mass makes the car change direction like a school bus. By comparison, Kodiak wheels are half the weight, and it's all saved in the rim shells. I've been kicking myself ever since...

Changed from OEM 2G AWD front brakes to TCE's SP-legal Wilwood kit, saving 4lbs of rotating unsprung mass and 7lbs non-rotating unsprung mass per front corner. Similarly, if you can't feel that you should consider switching to competitive beer drinking

Charles

 

[eclipsh]

Similarly, if you can't feel that you should consider switching to competitive beer drinking

Charles

You mean I can't do both?

Good information to have. Still, as every road racer out there seems to be looking for an increase in thermal mass over stock rotors and these are a decrease (however minor) it doesn't seem like a good move for a track guy. For Auto-X or drag racing where the breaks don't have time to heat up it does make sense. This combined with some brake ducting could work.

What is the weight difference between these and Cobra calipers though? Those are also aluminum and will take a thicker rotor.

 

[ACM]

You mean I can't do both?

Good information to have. Still, as every road racer out there seems to be looking for an increase in thermal mass over stock rotors and these are a decrease (however minor) it doesn't seem like a good move for a track guy. For Auto-X or drag racing where the breaks don't have time to heat up it does make sense. This combined with some brake ducting could work.

What is the weight difference between these and Cobra calipers though? Those are also aluminum and will take a thicker rotor.

I don't know the weight of the Cobra rotors, but 2G AWD rotors are a little over 14lbs each, whereas Todd's 12.2" OD 1" thick rotors are just over 10lbs. Given the size of a 1-piece Cobra rotor, one can extrapolate without too much difficulty...

Regarding the Cobra caliper, I don't know the weight, but keep in mind that's only part of the equation - there's the mount adapters and hardware to consider too. In the case of the radial mount Dynapros, that additional weight is 1lb 3oz - if that was steel it would be an awful lot more; similarly, if one were to use a non-radial mount Dynapro, my guess is that the 1lb 3oz would be halved.

The key to brakes is two fold - you need the right leverage to generate the stopping power, and the right heat sink mass to avoid fade. The larger diameter the rotor the higher the gyroscopic effect, and that slows down steering responsiveness (ok, perhaps not so hugely on a 3000lb DSM piglet and the more energy it takes to accelerate that lump of iron. The leverage you need depends on speeds, vehicle mass, available grip, the heat sink mass simply on the energy to be dissipated. If one is running low grip tyres or on a low grip surface a 10" rotor may generate all the leverage the mechanical grip can tolerate - but if the speeds are very high a much thicker rotor will be required compared to a low speed environment - local rallycross vs a WRC stage. It all depends on what you're doing. Yes it's safer to over-engineer, but it adds weight and slows the vehicle in multiple ways. The flip side obviously is that you never want to under-engineer a braking system !


All of this weight saving sounds like not very much, but when you add it all together it becomes substantial. For most cars, there's no 100lb redundant component you can throw away, it's dozens of minor components that need to be hunted down. In the same sense, when any component is added or changed be sure to pick the lightest possible functionally effective part, or all those pounds so slavishly removed are _very_ quickly added back in.

Charles

 

[Flash]

The cons of the larger rotors should be considered but should not overshadow the pro's. It won't slow the car down substantially. Any given day I would rather deal with a VERY slight decrease in acceleration over having to deal with a day of heat soaked rotors tiny rotors.
I'll have to weigh my rotors to see how much they are. I'll let you all know.

 

[awdcsm]

First off, the cool thing about aluminum is that not only does it shed heat quickly, it gains heat quickly (funny thing about those material properties is that they work both ways) You need to take steps to shield the caliper from getting hot in the first place. Powder coating hurts this.

Your "just some info" is misinformation.

Where does the magical 100 psi go?

You have ONE brake line going to each caliper whether it's a sliding or fixed caliper. This fluid either moves 2 pistons twice the distance (sliding caliper) or 4 pistons half the distance. Aside from the not quite negligible losses caused by friction on the sliding pins, you end up with very similar pressure and outputs. It has to cover the pads have to travel the same distance over all.

Your area of 5.93in^2 is correct for your example, however your area of a 4 pot fixed would be all four pistons. 7.06in^2
Pressure requirements for applying a pad to rotor are the same whether you have 10 pistons or 2.

The only benefits to fixed calipers are A) you never have to worry about frozen slides, B) there is typically more even pad wear, and C) a slightly better feel due to very slightly faster response from peddle application to brake force.

Hydraulic systems are pretty easy. Don't give out bogus information if you really don't know what you're talking about.


And don't try to call me out as being negative as I'm running 4 piston calipers... Just for the right reasons and not bogus ones. (Like being able to put monstrous track pads in ;-))

4pot = even surface area on pad to rotor contact front and back of rotor also less warpage
boooooooo
go bash someone else in another forum
were tryn to see how we can mount these

 

[drivemusicnow]

4pot = even surface area on pad to rotor contact front and back of rotor also less warpage
boooooooo
go bash someone else in another forum
were tryn to see how we can mount these

Please STOP posting incorrect information.

Rotors don't warp. Check out stop techs white papers. Deposits are left from the pad of a very hard carbon material. This has more to do with pad break-in and how hot they get than, and I quote "even surface area on pad to rotor contact front and back of rotor also less warpage"

Do you get how a sliding caliper works? If not, I'll draw you a picture to make it clearer.

 

[Todd TCE]

So I was having to help a buddy convert this huge mc threaded fitting to -3AN. It must have been M16 or such thing with an o-ring seal and then 1/2"IF outlet or whatever. It's on a Lightning truck. Can we get an adapter for this he says? Ahhhh....only if we stack up about 6 adapters one to another to some how get to what you want.

So...we pull the fitting and chuck it up in the lathe. Then we lop off an conventional -3 adapter of some sort to fit inside it. Tig it up (not me I suck at welding) and we're golden.

But as I was sizing the parts they were heavy! It was all I could do not to chop it all down on the lathe to remove 2oz of wasted metal! It's a sickness I tell you.

 

[KGB Pilot125]

Please STOP posting incorrect information.

Rotors don't warp. Check out stop techs white papers. Deposits are left from the pad of a very hard carbon material. This has more to do with pad break-in and how hot they get than, and I quote "even surface area on pad to rotor contact front and back of rotor also less warpage"

Do you get how a sliding caliper works? If not, I'll draw you a picture to make it clearer.

Rotors dont warp? Please oh please back this up so I may update the millions of techs and service writers that believe that rotors warp

 

[Todd TCE]

DTV: disc thickness variation.

The result of build up on one or more areas of the rotor's surface. Sometimes referred to as "hot spotting"- caused for example when one hold his foot on the brake pedal after a hard stop causing crystallization of the pad material upon the surface.

 

[KGB Pilot125]

DTV: disc thickness variation.

The result of build up on one or more areas of the rotor's surface. Sometimes referred to as "hot spotting"- caused for example when one hold his foot on the brake pedal after a hard stop causing crystallization of the pad material upon the surface.

I have a set of these in my shop right now that came off a MDX. they are warped and show hot spots on the rotor. but I also have "seen" warped rotors that showed no hot spots but you could feel the vibration in the brake pedal.

 

[drivemusicnow]

StopTech : Balanced Brake Upgrades


When I said "see stop techs white papers" I wasn't joking.

My actual point was to say that sliding calipers won't "warp" rotors more or less than opposed piston calipers.

 

[4g63thermal]

I was wondering if he ever got those on there im not trying to join in a which is better argument but i like the idea of the smaller 4pot rotor and was interested in maybe doing this to my car

 

[awdcsm]

iam gona order some soon from rockauto then make custom brackets that fit under my original tsi wheels

 

[ThomasG-1b]

So did anyone see if the rx7 brakes work?

 

[GRNDSM]

I have been told that these FD RX7 calipers are fairly low profile and are designed to work with .88" rotor (.77 low service limit). That could make them compatible with TCE's .81 rotors, given custom caliper mounts.

Does anyone have a set of these calipers on hand that they could measure?