Brent 89 - GT

I just finished installing my new set of GTS calipes and facotry cast hole big rotors <img src="graemlins/r.gif" border="0" alt="[king]" /> Just thought I would post a pic of those bad boys installed. I still need to flush the fluid with super blue and change the rear rotors and pads. I bought the cast hole Zimmermans for the rear and Hawk "plus" pads all the way around. I am thinking my brake fade days are GONE Of course i haven't had a chance to try the 928 out on the track yet but, brakes were always my nemesis on the 951.

I now have a pair of S4(GT) calipers for sale. The pads are 50% or better and would be free with caliper purchase looking for $250. brenth@wcta.net
Yeah Baby

Brent 89 - GT

OK, so why wont the pic load? I properly uploaded to Rennlist as can be seen by the address. I used "image" to try and put it in there. Any clues?

Shane

Let Me try



By the way they look sweet!
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Brent 89 - GT

Thanks Shane <img src="graemlins/wave.gif" border="0" alt="[byebye]" />

Gretch

Can you describe the difference between GT, GTS and "Big Red" brakes?

I have ordered the cast holes, shoes, pads and sensors, planning to stay with the GT calipers that came with the car. I am interested in why you chose to upgrade to GTS calipers vs Big Reds.

The holes do look great.

Ed Ruiz

GT brakes are the same brakes used on the S4 series, which was first installed in the 86.5 MY.

The GTS brakes are the same size as the "Big Reds" used on the 993 series. In most cases the 928 calipers were not painted red, but they were indeed the same size. Later, the 993TT calipers were enlarged, and all of them were painted red, so not all "Big Reds" are the same. The 996TT has yet even larger calipers and rotors than the 993TT. YMMV.

Gretch

"Bigger" is an interesting word, one in this instance, I am seeking the consequence of.....

When I asked Wally, he advised the GT (S4 as you have indicated) brakes were in his words "damn good brakes". As a result I have opted for a new set of holes for Gretch's Christmas present and passed on larger calipers.

I am interested in opinions of all "informed" parties on the merits of a caliper upgrade.

Ed Ruiz

As I have installed GTS calipers and rotors on my GT, I think I know something about them. As far as stopping power goes, the difference is hardly noticeable (assuming one uses the same type of brake pad). Where the is a noticeable difference is in reduced fade, especially at tracks where hard and sustained braking is required. Those larger rotors have considerably more mass to help disapate the massive amount of heat generated while braking hard. Slotted and cross-drilled rotors provide additional surface area to help disapate the heat as well as allow the venting of gases. The down-side to cross-drilled rotors is the cracks that occur that radiate outward from the holes. If such a crack were to migrate to another hole, the rotor could eat away at teh pad at a very fast pace, or it could even break apart.

If you do not intend to use the car on a track, then the OEM brakes are good enough, and as I said in an earlier post -"Save you money". YMMV.

Bill Gregory

[quote]<strong>
I am interested in opinions of all "informed" parties on the merits of a caliper upgrade.</strong><hr></blockquote>
Porsche brakes, from the factory, are usually pretty good. Bigger or larger brakes, for example moving from the S4's to the GTS brakes, entails new calipers which also handle larger brake pads (S4=250 cm2 in front; GTS=302 cm2 in front), as well as larger rotors (S4=304x32mm, GTS=322x32mm). If you can lock your existing brakes up, then moving to larger brakes will not stop you any quicker. The benefit of the larger brakes come, for example, in a track environment, where continuous usage of the brakes generates lots of heat and may boil brake fluid, not to mention the increased component (pads, caliper seals, rotors) wear and tear. Larger brakes have larger rotors for better heat sinks and larger pads which spreads out the amount of pad in touch with the rotor. Together this helps the brakes to run a bit cooler. (Ignoring the contribution of brake cooling, brake fluid, etc).

John Veninger

I ran my stock GT at several DE's. Used Hawk HP plus pads and also Hawk blues. Ran with ATE fluid.
Never had a brake issue. The only time they felt a "bit" softer was at Watkins in 98F weather at the end of the day. Not really an issue.
If your fading stock GT/S4 brakes I suggest looking at the fluid your running and pads.
I run stock S4 brakes on my lightened track car. Taking weight off is like upgrading brakes
Also remember S4/GT rotors and pads are much cheaper than GTS stuff.
My view is that upgrading S4 brakes to GTS on a street car is for looks only.

Brent 89 - GT

I only made the change because I intend to track the car some. The car is pretty heavy and I like to brake agressively. The tracks I would run have two to three heavy braking zones per lap, ie; 120-130mph down to 60-80mph. My past experience in a 951 was that I was always fighting the brakes. That car would have required a VERY expensive operation to increase the brake size. Doing this operation on the 928 was seemingly cost effective by comparison. I had the money and the time and I am tired of screwing with brakes at the track.

I agree with all who suggest that you save your money. You will never overdrive the stock brakes on the street. You would be in jail or dead before you could run that hard. Make sure you buy good pads and change the fluid annually, or every other year at the least.

The big rotors and calipers are good insurance agianst fade at the track. On the street they are a want, not a need.

Ed, are you running the 55bar rear bias valve with the GTS brakes? How do you like the set-up?

Gretch

Thanks for all the input. I really like the look of the cast hole rotors, and am very comfortable keeping the GT caliper set up based on the best expert opinions one could hope to find on the subject. Thanks Gents..........

Brent 89 - GT

Keep in mind that the rotors you ordered will not look quite like the GTS ones I fitted. Those are factory versions. What you will get is a cast hole Zimmerman like I have fitted in back. <a href="http://boards.rennlist.com/upload/holyrotorsrear.jpg" target="_blank">http://boards.rennlist.com/upload/holyrotorsrear.jpg</a>

Ed Scherer

[quote]Originally posted by Brent 89-GT:
<strong>[...] I bought the cast hole Zimmermans for the rear and Hawk "plus" pads all the way around.[...]</strong><hr></blockquote>
Regarding those Zimmerman rotors for the rear... I got those, too, and wound up pulling them off and painting the exposed, non-friction parts (the "hats") because they rusted so much that they looked pretty bad with my nice wheels. So... I'd just recommend that anyone that pairs the Zimmermans with nice wheels: paint them before you put them on!

I used <a href="http://www.ed.scherer.name/Porsche_928S4/6/project/IMAGE042.jpg" target="_blank">VHT flat aluminum and then some some VHT clear</a>.

<a href="http://www.ed.scherer.name/Porsche_928S4/6/project/index.html" target="_blank"></a> <a href="http://www.ed.scherer.name/Porsche_928S4/Slideshow5.html" target="_blank"></a> <a href="http://www.ed.scherer.name/Porsche_928S4/Slideshow5.html" target="_blank"></a>

--
Ed Scherer
<a href="http://www.ed.scherer.name/Porsche_928S4/Slideshow.html" target="_blank">'90 928S4</a>

Ed Ruiz

[quote]Originally posted by Brent 89-GT:
<strong>
Ed, are you running the 55bar rear bias valve with the GTS brakes? How do you like the set-up?</strong><hr></blockquote>

I installed the 55 Bar rear bias valve long ago. For normal street driving - there is no difference. On the track, the rear tires may want to lock-up first, but the ABS system will not allow them to.

The main advantage is that the rear brakes are contributing more to the overall braking effort. With the 18 Bar rear brake bias valve I would go through three sets of front pads for every set of rear pads. With the 55 Bar rear brake bias valve it's more like two sets of front pads for every set of rear pads. YMMV.