1G RX7 brake calipers fix 90 AWD?

[awdcsm]

my goal here is keep my stock 90 tsi wheels to retain sleeper look and still have braking superior to the 2pot calipers...
my first attempt to big brakes was upgrading to a 93 awd rotor and 2pot caliper but now i still want more braking power.
next i look into 3kgt vr-4 calipers but i would rather not add more weight with bigger rotors, rims, and fabbing custom brakets (RX7 1gen 4pots weight 5lbs btw)
so as i was searching the web i came across some 86-91 sumitomo 4pot rx7 front calipers. they look very similar to the 3kgt vr4 calipers but a smaller version. as we know rx7s have 16" wheels so these should clear my stocks
so i did more research, the dimentions of a 1990 rx7 and tsi rotor are very similar.
as you can see on a rx7 caliper bolt hole brakets are shorter than 3kgtvr4's are. so i was wondering if it is possible to bolt them up to a 90 awd knuckle.

http://www.s248849158.websitehome.co.uk/Data/300209/2236middlemagregs_thisnthat/1.html

if anyone has a rx7 4pot caliper and can possibly mock it up to see if it fits on 90-94 awd, it would really help my researh thanks.

 

[sbiggi]

What is wrong with the 2pot dsm calipers?

Guess I dont see the reason to go with a 4 pot caliper on the same size rotor if the 2pot can already lock up the tires. Just going to a 4pot caliper isnt going to do anything for you.

 

[habitatguy187]

What is wrong with the 2pot dsm calipers?

Guess I dont see the reason to go with a 4 pot caliper on the same size rotor if the 2pot can already lock up the tires. Just going to a 4pot caliper isnt going to do anything for you.

1g small calipers 12lbs. per side...

1g big brake twin piston calipers 14lbs. per side...




9lbs per side of unsprung weight? Sounds sweet to me.

 

[123abc]

They must be aluminum calipers then? That would be nice if they matched up better than the vr4 setup.

 

[awdcsm]

therefore aluminuim is lighter and will displace heat 1.5 to 3 times faster than the cast iron or steel calipers. This is important when the rotors heat up to 1100 to 1200 degrees.

OEM (floating) vs 4 piston (non floating): Most of the brake kits currently being sold are single/dual piston OEM type calipers. In order for the caliper to squeeze the rotor it has to use a floating design, otherwise it would only apply pressure from one side to the rotor. Because of this design you loose approximately 100 psi. 4 piston calipers squeeze from both sides and are fixed (don't float), so they (4 piston) do not require as much pressure. The single/dual piston caliper also requires more volume to work. The area of a 2 3/4" single/dual piston caliper is 5.93 si VS the area of two (2) pistons on a 4 piston design of 3.53 square inches. (you only multiply by 2 piston to get the area because the other 2 pistons are being apply at the same time to squeeze the rotor, unlike the one piston design) anyway 5.93' si VS 3.53 is a big difference. Does the volume effect the braking? Yes, it has a great effect on the master cylinder volume that is required for all 4 wheels. This will mean you will have to use a larger diameter master cylinder to meet the requirements of the calipers. The larger the master cylinder is the lower the pressure output.

just some info

 

[duwackerTSi69]

If anyone is interested, I have the 2g RX7(86-91) 4 pot calipers, and am willing to sell them?

 

[habitatguy187]

If anyone is interested, I have the 2g RX7(86-91) 4 pot calipers, and am willing to sell them?

Pics?

 

[KGB Pilot125]

Trying to get a RX7 one now

 

[duwackerTSi69]

Pics?

Ill get some pics later on this afternoon. They have been powder coated fire engine red and where they say RX7, I sanded off the powder coating to give them a brushed aluminum look.. They can easily be redone, and this time shave off the RX7 lettering that way you dont have rx7 badging on your dsm.. Powder coating is apprx $30 for a set of 2 in either glossy black, white and fire engine red. Pics comming soon.

 

[KGB Pilot125]

I am having one delivered tomorrow from the parts house. I will measure anything that anyone needs just let me know. I intended on measuring the mounting ears and comparing them to a 1G 2 piston

 

[eclipsh]

What is the width of the stock Rx-7 rotor that goes with the caliper? Most of the road racers here seem to complain about the lack of heat sink in our stock brakes, not the torque available. If they use thicker rotors that'll be a big improvement for a lot of guys.

 

[KGB Pilot125]

Got the caliper in my hand and boy is it light. I forgot to grab my 1g caliper from home but if someone wants to measure one I can measure this and we can compare. I also really like the idea if the quick change pads.

Josh

What is the width of the stock Rx-7 rotor that goes with the caliper? Most of the road racers here seem to complain about the lack of heat sink in our stock brakes, not the torque available. If they use thicker rotors that'll be a big improvement for a lot of guys.

Looking through our book here at work I find that thickness for a 93 TSI is .94 inches and for a 91 turbo RX7 its is .89 inches. The gap on the caliper is about 1.011 inches dont know how accurate the mic is but it has to be closer than me and a tape measure!

EDIT:

There are some pictures of the two calipers side by side. The weight difference is amazing. The calipers are not a direct bolt on but I might pursue this further becuase I like the idea of light weight and being able to run my 16 inch wheels, I have 3 sets of them and I dont want 17's. Cannot give a time line for this but hopefully soon.

 

[eclipsh]

So it uses a thinner rotor? I guess it could be a weight savings for drag racers then but it will not be of any use for road racers. Still, I wish you the best of luck on it.

 

[KGB Pilot125]

So it uses a thinner rotor? I guess it could be a weight savings for drag racers then but it will not be of any use for road racers. Still, I wish you the best of luck on it.

Thinner by hardly anything, I think with the aluminium caliper this would actually cool better than the steel ones. I am going to try it out soon like I said. I have to put my brand new KYB AGX's on that I just got for free

 

[drivemusicnow]

therefore aluminuim is lighter and will displace heat 1.5 to 3 times faster than the cast iron or steel calipers. This is important when the rotors heat up to 1100 to 1200 degrees.

OEM (floating) vs 4 piston (non floating): Most of the brake kits currently being sold are single/dual piston OEM type calipers. In order for the caliper to squeeze the rotor it has to use a floating design, otherwise it would only apply pressure from one side to the rotor. Because of this design you loose approximately 100 psi. 4 piston calipers squeeze from both sides and are fixed (don't float), so they (4 piston) do not require as much pressure. The single/dual piston caliper also requires more volume to work. The area of a 2 3/4" single/dual piston caliper is 5.93 si VS the area of two (2) pistons on a 4 piston design of 3.53 square inches. (you only multiply by 2 piston to get the area because the other 2 pistons are being apply at the same time to squeeze the rotor, unlike the one piston design) anyway 5.93' si VS 3.53 is a big difference. Does the volume effect the braking? Yes, it has a great effect on the master cylinder volume that is required for all 4 wheels. This will mean you will have to use a larger diameter master cylinder to meet the requirements of the calipers. The larger the master cylinder is the lower the pressure output.

just some info

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 ;-))

 

[Todd TCE]

Nice reply. I read that and found it full of holes also.

The loss of 100psi is not quite right....given a floating or sliding caliper is less efficient and does not have the quick response of a fixed mount design I'll take it to mean that there is an excessive amount of DISPLACEMENT of fluid but that's not pressure. Once on contact with the rotor the pressure is the same if the area is the same and input the same.

FWIW, caliper piston area is defined as 1/2 the caliper body to compensate for the slider design. Not 2x the actual size on one (and only in a single) side. In most cases a properly paired system would not require any change in mc.

 

[Flash]

1g small calipers 12lbs. per side...

1g big brake twin piston calipers 14lbs. per side...




9lbs per side of unsprung weight? Sounds sweet to me.

You won't feel the 9lbs per a side, this isn't F1 and most everyone on this forum isn't a pro driver to have such an acute sense of feeling. Weight isn't everything.

 

[Rob10_99]

Also, for the 2 piston being able to "lock up" the disc is irrelevant, it's about modulation and peak torque capacity. If you can lock up a 20" 50lb chrome wheel on the freeway at 80mph with a stock brake system, why would anyone make big brakes for anything?
Modulation lets you use that peak force before it locks up and sends you into another car or the wall.

 

[Flash]

Why do people get so excited about 'bigger' brakes or the number or pistons they have when they use tiny rotors. Or when they install the brakes they run crappy pads and rotors that warp. Is this an image or status thing?

 

[KGB Pilot125]

Why do people get so excited about 'bigger' brakes or the number or pistons they have when they use tiny rotors. Or when they install the brakes they run crappy pads and rotors that warp. Is this an image or status thing?

Not trying to start anything because I agree with you to an extent but I would like run a 4 piston rather than the single sided single piston or single sided dual piston because its a better design. Kinda like why have a stack dash in a street car? little over kill and some people would think that its only for looks!

 

[Todd TCE]

For the budget minded drag racer that 2lbs may be worth taking. Granted probably won't show up on the clock but a little here....a little there....I know how that works personally.

While fine for his needs the twin pot setup offers improvements for pad wear and durability not needed on the strip. From there the move to multi piston calipers goes one step farther by offering improved response, often beefier pads, a change in area, fit to a larger disc or whatever the intent is. Just more flexible options.

I agree that fitting a lot of that to a small rotor is somewhat counter productive. For durability there's no sub for more and larger rotor mass regardless of the caliper and pad.

 

[KGB Pilot125]

For the budget minded drag racer that 2lbs may be worth taking. Granted probably won't show up on the clock but a little here....a little there....I know how that works personally.

While fine for his needs the twin pot setup offers improvements for pad wear and durability not needed on the strip. From there the move to multi piston calipers goes one step farther by offering improved response, often beefier pads, a change in area, fit to a larger disc or whatever the intent is. Just more flexible options.

I agree that fitting a lot of that to a small rotor is somewhat counter productive. For durability there's no sub for more and larger rotor mass regardless of the caliper and pad.

Personally I would like to do it because of the reasons you mention above plus I can keep the 16 inch wheels. I have 3 sets plus track tires are about half the price for me. Not to mention another really cool feature is the pads are easier to change if your doing a pad slap.

 

[habitatguy187]

You won't feel the 9lbs per a side, this isn't F1 and most everyone on this forum isn't a pro driver to have such an acute sense of feeling. Weight isn't everything.

I would venture to say that you would feel a difference in 18lbs of UNSPRUNG weight. Match those with a set of lightweight wheels and tires and you're set.

 

[PieEyedPiper]

I would venture to say that you would feel a difference in 18lbs of UNSPRUNG weight. Match those with a set of lightweight wheels and tires and you're set.

If people can detect an increase in low speed driveability with lightweight wheels, then why wouldn't you notice 18lbs off your calipers?

I'm in agreement. 18lbs is enough to notice, possibly enough to make a difference.

 

[Flash]

The bottom line is I am a person with light-weight wheels and I don't notice a difference in low speed drivability. I have forged aluminum calipers and I don't notice a difference. But that is all OK because I purchased all those parts without weight at the forefront of my decision making process. Someone already mentioned the thermal properties of the calipers. Just because you can fit a calipers with more pistons on your car doesn't mean it will always equal an improvement when you run tiny rotors and crappy pads. They said this to me when I joined in 2003, good rotors and good pads take you a long way and I think it still applies today, anything more and you should just call Todd at TCE.