Project GD STI- Getting it Slowed Down with Stoptech

By Mike Kojima

The Subaru GD STI comes with pretty good brakes from the factory, big Brembo 4 piston front and 2 piston rear calipers squeeze big vented rotors. In other words the stock brakes are already quite good, what would have been state of the art just a few years ago. This means we would have to be careful when it comes to modding them, it is easy to mess things up and actually do worse than stock with a poorly engineered brake upgrade.  So why would we want to change them out with something else?  The main reason is that since our car is going to see some occasional track use, we want to upgrade our brakes so we can drive our car to the track for an event without the hassle of having to switch pads at the track.  The big brakes will allow us to run at speed on a streetable brake pad.  Bigger more powerful brakes will also be easier to modulate. The third reason is admittedly that big brakes just plain look cool!  We went with Stoptech as the brake system of choice for their combination of daily driveability and track performance.  We selected Stoptech's Trophy STR big brake kit. 

Read more about Project GD STI here!

Our Stoptech STR Trophy kit came with a large 14" or 355mmX 32mm slotted rotor.  The hat is hard anodized for corrosion resistance.
The rotors have a proprietary low turbulence vane design which greatly improves airflow throughout the rotor for better cooling. The vanes are staggered at the inner diameter entrance for more air intake and are airfoil shaped in profile. In benchmark testing of the Aerorotor, it had the best airflow of any rotor on the market.  The Aerorotors are also directional so you don’t have reversed vanes on one side of the car like many other rotors. Better rotor cooling leads to longer life, less fade and greater resistance to warping.
The Stoptech hats have vanes in them to pump air between the rotor and the hat to reduce the amount of heat transfer to the wheel hub and bearings, an interesting touch.
Stoptech floats the rotors using a special shoulder bolt which allows the rotors to move on the hats even when fully tight.  This helps reduce caliper piston knockback and reduce rotor coning when hot. Normaly the rotors are sent fully floating which is better for racing but we had the rotors built with anti rattle washers.  A heat resistant Inconel cone spring washer shown here allows free play but has enough preload to reduce rattling, the fully floating rotor's only real disadvantage.
The Trophy kit features an enhanced version of Stoptech's venerable ST-60 six piston caliper.   The Trophy calipers feature a forged aluminum alloy body. Forging is a superior method of forming aluminum when an aluminum billet is heated and basically smashed into shape using many tons of force into a die.  Forging produces a part with compressive stress for increased strength.  It also orients the metal's grain in alignment to the part's shape.  Putting the grain in the right direction increases strength and dimensional stability, much like how putting the grain of a piece of wood in the direction of stress makes for a stronger wood part. The pressure and stress of working the metal during forging also refines the aluminum's grain making it finer and eliminating voids and other internal flaws that can weaken the structure.  This also makes for a much stronger part.



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Thursday, November 08, 2012 4:39 AM
Are those titanium retaining bolts on the rotor hat?

Aslo, concerning the rear parking brake (and I might be way oversimplifying it) but couldn't stoptech use a second small brake caliper for your parking brake (a la ferrari)? The cost of the rear brakes would definitely jump, but it would probably reduce a ton of weight removing that integral unit.
Dan DeRosia
Dan DeRosialink
Thursday, November 08, 2012 5:23 AM
Heh... even as I wonder how other alternatives (the AP setup for one) stack up, I have to say the Stoptech stuff is pretty sexy.

Also, the canister looks different than the pics of the KW Clubsports that went on in part 2; can you share any details of what's going on there, or should I just be patient for more parts of this series?
Thursday, November 08, 2012 6:11 AM
I always wonder about removing the dust shields. Is there any concern about radiated heat cooking the cv joint boots? When I threw a brake kit on my B5 S4, I just trimmed the shields and bent them back a little.
Mike Kojima
Mike Kojimalink
Thursday, November 08, 2012 7:05 AM
The hardware is not Ti. The issue is that the rear spindle is difficult to mount more stuff to without having a really big and odd bracket but it is possible. It would add a lot of weight and complexity to a already pretty good stock rear brake.

I didn't check AP but Brembo does not have a rear upgrade for this car and only Girodisc makes a two piece rear rotor. You have to mill your pads down for the Girodisc rotor to work so I didn't bother.

For dustshields I have never had anything happen by removing them and all of my cars I have owned in the last 15 years including race cars, have had them removed. Brake dust gets on the suspension. It is the only downside I can see.
Dan DeRosia
Dan DeRosialink
Thursday, November 08, 2012 8:19 AM
The AP kit put together by Essex is only 332mm rotors, but uses the Superlite pad shape, and 2 piece AP rotors; seems like it would have less cost in consumables, but its obviously smaller and only 4 piston. There's 6 piston kits with similar sized rotors to the Stoptech and a 4 piston rear kit with bigger rotor that looks like it retains the ebrake... but it uses a (bigger; 335x24) one piece rotor. CP7625 for the rear, CP7040 for the 6 piston front. Price is probably up there being AP, but Stoptech isn't free either.

This is not to argue against Stoptech, just to point out other high end options.
Mike Kojima
Mike Kojimalink
Thursday, November 08, 2012 10:59 AM
That must mean the Stillen exclusive on street car AP brakes must be done.

I would like to try a caliper with anti knockback springs like the AP. This would help on cars like the 2004 STI with weak hubs.

Do you have a link to the rear kits? It looks to me that essex only has a front application.
Wrb kid
Wrb kidlink
Thursday, November 08, 2012 11:15 AM
Rotora also offers a four pot rear with two piece hat that retains the e- brake. We have it on our race car. The fronts are six pot with titanium vented pistons with anti knock back springs. We have 04 sti hubs and have ran two years with no type of bearing problem. Just ask Clint. The set up we run is the super challenge rotoras
Dusty Duster
Dusty Dusterlink
Thursday, November 08, 2012 11:21 AM
The S197 Mustang simply uses the rear brake calipers as parking brakes. The parking brake cable squeezes the rear brake calipers.
Dan DeRosia
Dan DeRosialink
Thursday, November 08, 2012 11:42 AM
Essex is the/an importer for race calipers; the ones in their kit are technically not street pieces, I think. Stillen has the setups I mentioned on their site, looking at it; direct linking is hard on my phone, but it's under the Formula brake kits.
Mike Kojima
Mike Kojimalink
Thursday, November 08, 2012 11:44 AM
Had some issues with Formula kits before. I would rather run stock. I would rather not run Rotora either.

We have had problems with knock back and steering centering and feel on both 04's we were familiar with. Note that our first GD was an 04. This is the main reason why we resumed the series with an 05.
Der Bruce
Der Brucelink
Thursday, November 08, 2012 12:47 PM
Would Motul 660 have any issues with the occasional Northwest freeze or is there no temp/moisture concerns?
Mike Kojima
Mike Kojimalink
Thursday, November 08, 2012 1:46 PM
Motul is really good with moisture.
Dan DeRosia
Dan DeRosialink
Thursday, November 08, 2012 5:09 PM
No experience on the Formula kits myself, just knew they existed. The anti-knockback springs make the Essex AP kit look pretty attractive for what I'm doing, as I've got a bugeye with the spindles that implies.

Of course, that sort of depends on the whole question of where I leave "good enough" at. I've every intention of *not* tracking it, but still want something that I don't feel is lacking... and that I can put snow tires on without swapping different suspension/brakes. Ah well.

Motul is just really good stuff in general. It's one of those things that makes brakes work on the stuff I'm familiar with. And if EProd RX-7s, with dinky 250mm rotors and stock calipers, can survive running a half hour sprint race at Road America without boiling fluid... it always makes me scratch my head a little at people insisting on the need for big brake kits. "Need" is different from "want", and "want" is perfectly valid, I full well acknowledge.
GT Flatout
GT Flatoutlink
Thursday, November 08, 2012 5:36 PM
By modulation are you talking about hard braking? Why is there the need to modulate the pedal on an ABS equipped car?
Mike Kojima
Mike Kojimalink
Thursday, November 08, 2012 5:41 PM
Yes, even with ABS there is plenty of need to modulate brakes.
Thursday, November 08, 2012 8:43 PM
I learned to track a car without ABS, so ABS throws me off a bit sometimes. Anyways, yes, even with ABS, you need to be able to modulate. For example, trail braking into a corner where you're also controlling the attitude of the car during turn-in.
Saturday, November 10, 2012 10:35 AM
Did you have to change bmc to account for the larger calipers/overall piston size and what did it do to the brake balance?

With dust shields it only takes one time to get a stone caught in between the shield and the rotor for you to rip them off on all future cars :)
Dan DeRosia
Dan DeRosialink
Saturday, November 10, 2012 6:41 PM
Hm; Hoerr Racing Products has PFC anti-knockback springs, says they work retrofitted into other calipers too. Wonder if that would be worth a try on the 5x100 Subaru spindles. They're like, $8 for a pack of 4. May have to try it on a non-Brembo 4/2 pot setup.
Mike Kojima
Mike Kojimalink
Saturday, November 10, 2012 9:20 PM
Properly engineered brake kits like Stoptech don't need MC changes.
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