1G 1- 2-piston brake calipers

[TheRealMRDyno]

Hi,

I have a 1991 AWD Talon, and the stock brakes are terrible.

The web is full of comments that the 2-piston 93/94 brakes are much better.

Bigger rotors is better for heat rejection, but I lack braking force, too.

I can not find reliable values for the piston diameters for the 1- and 2-piston calipers - I did find one post that gave diameters such that the 2-piston calipers would generate about 70% of the clamping force of the 1-piston calipers - that is a bigger reduction than the increase you get from the larger effective rotor diameter, a net loss in braking force / pedal force.

So, does anybody have these brake piston diameter numbers? I just cant see changing over to the 93/94 brakes when the only values I have indicate a loss in performance - hopefully those values were wrong, but the amount of bad information on the internet makes me pretty wary of jumping on any bandwagons.

Thanks for any help!

 

[viprez586]

It's not bad information. I didn't measure mine when I swapped them over but the pads are way bigger and you take two pistons and spread them out over a larger surface area and it's a no-brainer your braking power will increase.

Don't expect big brake performance out of this. It is an upgrade from an OEM bolt-on application perspective. Relatively less brake fade from 100mph+ is the biggest difference you'll notice. The daily street driving you do...yes you'll notice a difference but it's not huge.

That being said pads will make the biggest difference. I run Hawk HPS front pads, they're good but I wish I would've went with something more aggressive for my likings.
Are they a good street pad? Hell yes.

Please research it more, you'll find most information on here is good and accurate.

 

[Colt4G63 also]

I did the upgrade to two piston calipers and 276mm rotors, and there's more to it than clamping force.

Think of this: If you put slicks on your car with lightweight wheels, your still getting better traction despite the fact that your car is now lighter. If clamping force was the only variable, you would have less traction with slicks because the car is lighter and therefore less clamping force (gravity) holding it to the ground.

Now alternatively think of this: 276mm rotors are like a longer breaker bar handle, and the larger pads are like a stronger grip on that breaker bar handle. Also the rotors have larger mass to absorb and dissapate heat. Like the previous poster mentioned, the results are most evident at high speeds.

 

[steve]

From the 93 FSM

Single Piston Caliper
256mm rotor 24mm thick
60.3mm piston

Dual Piston Caliper
276mm rotor 24mm thick
41.3mm x 2 piston

 

[TheRealMRDyno]

Thanks for the info guys.

Those FSM values come out to about 8% more torque from the larger rotors, and about 6% less clamping force from the (2) smaller pistons, for net of about 1.6% more torque / PSI. I know the pad area has some effect on the braking torque, but it is not large, I suspect it is about a wash.

I think maybe the pad's coefficient of friction may be the biggest, easily affected variable in this mix, I will try to see if I can come up with friction coefficient values for some different pads (unless anybody already knows some!).

In reality, these brakes are just not OK. It looks like the Mustang Cobra/Bullitt brake setup is where I will end up, seems like the best bang/buck deal around.

This 1991 TSI only has 18,356 miles on it (first titled 2006), and this is the first modification that it is going to get. I fought crap brakes on my 1990 from about 1993 to 2003, this time around I want to solve that problem once and for all.

Thanks again.

 

[dsmdeliveryboy]

I did the "Big brake" upgrade on my 90 with lighter wheels and felt a huge difference in stopping power, but your right the Cobra brake upgrade is probably the best bang for your bucks. I was thinking about doing that for awhile, but other things always seem to prioritize over doing that since I already put the dual piston calipers on..

 

[steve]

While there are other more expensive upgrades I don't think there are more cost effective ones.

I had the original calipers from day one when the car was new and would go though pad and rotors about every 20k. Had them replaced three time under warranty because the rotors would warp. Once I swapped to the dual piston caliper no more warping and a night and day difference in performance that your numbers don't support. It's not just pad friction, I had a chance to run a few different pads since including stock ones and Porterfield R4S, so I'm left wondering about your math.

They aren't track brakes, a couple of hard laps at RA would destroy them, but a major improvement over the factory brakes on the street or hauling the car down from trap speed. I'm just sorry that I didn't have/make the dealer swap them in 93.

 

[viprez586]

Wow, I wish I owned my car from birth. It'd look as nice as yours!

20k is ridiculous on brakes that do not perform.

Some of our cars do on average 30k. Mainly heavy sedans like the LS430 + 460.
The IS250, 350, and F tear through front brakes as well, but it's comparable to Big Brake kit performance.
Well...the IS F has Brembo 6 piston big brakes. Hello $3k brake job.