Caliper question G-Model

[Flojo]

Hello,
in my quest to upgrade my brakes, I just heard that apparently the BMW E23 caliper (ate, 4 pistons) fits 1:1 to the G-Model cars.
Only adaptation needed is to slightly bend the brake brass line to reach the thread in the caliper.

Can anybody cornfirm that?

[Flojo]

[Litle brother]

Interesting
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[manbridge 74]

Wasn’t there a BMW aluminum caliper that works?

[darrin]

how does this mod upgrade braking performance? Does it allow one to run bigger/fatter rotors to reduce fade/increase heat dissipation?

[chrismorse]

What is the mounting bolt spacing ?? 3 or 3.5 inches?

Manufacturer?

What is the throat width?

Piston diameter(s)?

It looks like cast iron, or is it aluminum?? Weight??

do you know the diameter/width of the stock BMW rotor??

Are pads readily available??

curious,
chris

[Flojo]

Chris, this is why I ask this forum.
I don’t know.

[darrin]

put another way, stock SC brakes should have no problem skidding your tires/exceeding their grip threshold when pushed hard. Improvements from Bigger/"better" brakes generally stem from reducing fade caused by rotors' inability to dissipate the heat accumulated during repeated heavy braking. Bigger calipers alone won't do much to help this situation and the potential for a different balance caused by introducing new front and rear brake calipers into your existing system can actually compromise braking performance.

[Flojo]

What about the benefit of 4 pistons vs 2, in case one fails/sticks?

[eastbay]

There is a fair amount of info on the 914 boards about this mod for the 3" space struts. I looked into it awhile ago for a car that had the 3" struts but never pursued it.

[Bill Verburg]

ATE did make a 4 piston caliper w/ 88.9mm(3.5") mounts

there were several versions
the smallest pistons were 4x40mm, a bit more piston area than a 930 caliper.

the 4 x40 w/ 3.5" mounts was designed for 22x290mm rotor, SCis 282x20 & C3.2 is 283x24

the 4x44 for 16x340 rotor
the 48/57 for 380x30

the best upgrade is still 930 4x38 on 32x304f w/ 930 4x30 on 909x28 rear

[Flojo]

Thanks bill

[Geronimo '74]

Originally Posted by Bill Verburg

ATE did make a 4 piston caliper w/ 88.9mm(3.5") mounts

there were several versions
the smallest pistons were 4x40mm, a bit more piston area than a 930 caliper.

the 4 x40 w/ 3.5" mounts was designed for 22x290mm rotor, SCis 282x20 & C3.2 is 283x24

So what does this mean regarding interchangeabity?
Possible to use the BMW calipers or not?

[Bill Verburg]

Originally Posted by Geronimo '74

So what does this mean regarding interchangeabity?
Possible to use the BMW calipers or not?

It means that you would have to find an appropriate rotor that would be an upgrade for the C3.2 24x283 and then a rear caliper/rotor combo to balance the front.

a 911 has the following rotor choices each dictated by a caliper set that can be used, some are better than others in terms of bias, the list is generally in order from least to highest thermal capacity

283x20 & 290x20
283x24 & 290x20
283x24 & 290x24
318x28 & 299x24
315x28 & 309x28
304x32 & 309x28
322x32 & 322x28

[kent olsen]

Ok what's a "G" model. Lordy the guys in my corvette group have done the same, C1, C2 and up. Give us old guys a break just tell me the year, ha ha.

I put SC calipers on the front of my 72 911. They gave me about 20% more swept area and were bolt on. I also have drilled/slotted rotors to help dissapate the heat. Also my car only weighs 2200 lbs.

I'm just a street and track junkie but I've never had any brake fade issues. Now I'm only running 205 X 50 x 15 tires so to much brakes would just lock up the tires, my opinion.

[manbridge 74]

G model refers to a 1974 911 but also it’s the same shape car from 74-89 so they are all lumped together. The 73 was an F model, 72 an E etc. In the US is where the year is focused on so much. In the UK it’s more what series the car belongs to, MKI, MKII etc.

[Bill Verburg]

Originally Posted by kent olsen

......
I put SC calipers on the front of my 72 911. They gave me about 20% more swept area and were bolt on. I also have drilled/slotted rotors to help dissapate the heat. Also my car only weighs 2200 lbs.

I'm just a street and track junkie but I've never had any brake fade issues. Now I'm only running 205 X 50 x 15 tires so to much brakes would just lock up the tires, my opinion.

The heart of any brake system is the rotors, they should be matched to the thermal load that they will be required to process. The thermal load in turn is determined by the weight of the car, the speed potential of the car and cycling time that the brakes will be expected to endure.

an early lighter car w/ stock relatively low hp/torque curves will be fine w/ stock A or S fronts on 283x29 rotors w/ M rears on 290x20 rotors. particularly if additional supporting steps such as pads that can operate efficiently at higher temps & w/ thermal brakes, fluid that can efficiently operate at higher temps and additional cooling air flow to the fronts.

You are also correct that brake torque useability is limited by the tires along w/ bias and suspension setup.

a +1 step from there is to use C3.2 front calipers and rotors

a +5 step from there is a 930 setup

and a +5 from that is a 993RS setup

[kent olsen]

Bill your advise is always expert and I'm sure from experience, which is the best kind.

I see many times individuals going overboard in some of the upgrades to our cars. When I first got my 911 20 years ago I couldn't afford the power upgrade I wanted so I went the cheaper way and removed weight, a little fiberglass here and a little there. M&K muffler 10 lbs vs stock at 30 lbs. It's really all about power to weight and then balance front to rear with some good corner balancing.

Maybe it's because I've had this car for 20 years and driven it on 8+ different race tracks but it is so stable and neutral handing I just love it. Now I have a classic Mini Cooper and I'm learning to handle front wheel drive, so far just autoxs. I've also added to my garage a 65 Corvette, this one unique, with a 392 Hemi. Here we are again with lots of power/torque and front engine and rear wheel drive. After some modifications to the rear suspension, oh yeah it has a Chrysler solid rear axle, I'm surprised at how it now handles as well.

As you can see I'm just a retired car nut that loves those old hot rods.

[Flojo]

Originally Posted by Bill Verburg

a +5 step from there is a 930 setup

Unfortunately very expensive...