I thought you guys might want a first look at this all new setup that will fit your stock 16" GTA crosslace wheels. These conform to the new SCCA rules which allow a Wilwood FSL 4 piston caliper teamed with a 12.2" x 1.25" rotor with an aluminum hat. These clear GTA wheels with NO rubbing and NO spacers needed. I finished the test setup today and the final version will be done in a week or so. First thing you'll notice is that the rotor hat isn't drilled yet, I wanted to make sure I had my math right before I drilled the hat and couldn't send it back in case I was wrong. I also noted the clearance between the caliper and wheel, about 1/4" in the areas I circled in red in the last pic. I tested them on a REAR GTA wheel so a front wheel will give a bit more clearance to the inside due to the 4.75" backspacing (Rears have 5.25" BS).

A big THANK YOU to Vern for shipping the wheel to me, your timing couldn't have been better. I'll get the rotor weight posted sometime soon, I'm sure you guys want to know exactly how much this thing weighs and how it compares to C5 and C4 HD rotor weights as well.

Enjoy!

Ed

 

Back:

 

Back side:

 

In wheel:

 

Here's the areas of tight clearance but without issues, I have about 1/4" or so in these areas:

 

Can I ask how much?

 

ed does it again!

i got my calipers from http://www.jrmotorsportsltd.com/ i think they were like $115 each

 

JR Motorsports has the calipers for $130 each now, Summit sells them for $154. The price has definitely gone up recently. I bought my test calipers for $112 each before they went up. But you can expect $130-160 per caliper. The hat was @ $80 and the rotor can vary from $50-120 each. Rotor bolt kit was $10. I haven't got the final amount figured yet as I don't have all the parts and I will be supplying a stronger, thicker (casting) rotor than you see here. But you're easily looking at $1000-1200 or so depending on rotor and pad choice. As I mentioned, this setup is designed for a SCCA car so it will be a strong and dependable setup.

Ed

 

If you already have an LS1 conversion, is it as simple as a new bracket, caliper, and rotor?????

 

Hmm JRMotorsports, they are basically in my back yard. If you need anything let me know how I can help.

 

Nice timing Ed. I've just tentatively agreed to buy an 89 GTA this afternoon. Guess I know where to go for my brake upgrade! I still need to get back with you regarding fronts for my Formula too.

 

which hub is that?

 

Standard hub used here. I wanted to keep the addition to offset at a minimum so I used that one. You could always use an HD hub but that added offset, along with the .500" thickness of this specific hat, would add .810" or so PER SIDE to your track width which is a bit too much with stock wheels. If you were running spacers and shortened them accordingly it wouldn't be a problem.

"If you already have an LS1 conversion, is it as simple as a new bracket, caliper, and rotor?????"

Pretty much.

Ed

 

No problem, glad I could help out!

 

Can the standard C4 be upgraded with minimal fuss? Too bad you didn't catch me before I ordered several goodies for the bird.

 

Yes, pretty much the same way as the LS1 setup would..

Whatcha doin' to the Bird now? I thought that thing was perfect as it was?

Ed

 

Not much,just a little of this.........a little of that. You going to be home this Saturday morning? I'd like to check those brakes out.

 

Yep, I'm off until December 30th...

Ed

 

Let us know what you think of the new brakes. I have been holding off on the c4 like you have ( I want to stay with GTA wheels) due to lack of time and my parts to install pile is out of control. Eventually I will get them from Ed or these new ones.

Only minimal difference in rotor size (keep in mind here I am strictly talking C4...NOT C4HD). C4 vs the new Wilwood setup.
All agree on here the rotor size is where it is at. However 4 pistons versus two has to be significant but unless one does autocross would it really be cost effective ? I guess to me the question is how much difference (on the street) would I notice
between the two piston caliper and the four piston Wilwood ?

Chime in here. Ed...please ? This new setup push the wheel out any further than the C4 ? Thanks.......................

 

I currently have the C4 and I love them. If the cost is right I may upgrade later but for right now I just want to get a look at what the mad scientist has come up with.

 

I did Mike's brakes (Mongoose) as one of my earliest kits when the standard 12" C4s were getting popular and before "we" knew we could go any bigger. I ran them on my RS before I had the HDs and really liked them, very good setup for the money.

This new setup will add only .200" more per side due to the thickness of the aluminum hat. The C4 hat is .300" thick, this one is .500" so it won't add much more at all. These brakes should make a huge performance impact, especially when compared to your stock brakes...night and day difference. For the comparison you mentioned, here's the specs:

This Wilwood setup: 4 piston FSL, 12.2" x 1.25" rotor;
Standard 12" C4s: 2 piston C4 PBR caliper, 12" x .81" rotor

These brakes are a good bit bigger than the 12" C4s, especially in thickness, which is good for heat absorption. Additionally, the pistons will push against each other instead of pushing on the caliper body which will again improve performance. These are top notch brakes for the GTA wheels.

Ed...Ahem.... Dr. Ed

 

So one could swap front to rear and vice versa on the GTA wheels
to make up for .500 on each side ?

Pad availability on these calipers ?
These calipers a good match for the rear PBR factory setup ?

How about anyone with this type of calipers chiming in here on how they act on the street ??????

Ed, You are a mad scientist but keep the wheels turning in that head of yours because we like the way you think...lol

 

Uh, you can't put "rears" on the front, right? Only the other way around (I'm running 4 front GTAs right now....)

 

Yes, the added BS of the rear wheels will negate the added offset of the rotor hat.

Vern, yes you can run rears on all 4 corners in a case such as this for the reason I described above, added offset. On a stock brake setup, I believe the steering arm will hit the rim of the wheel if a rear is placed up front. The buyer of this particular kit runs all 4 front wheels, I addressed this issue with him when I spec'd the parts.

As for pad availability, I supply Hawk HPS pads in my Wilwood street kits and will supply race compounds from Wilwood, EBC, and others as requested. Some guys also like to supply their own which makes my job easier, they already know what they like.

Ed

 

You can run rears up front with the C4 kit if you use a .25" spacer. I had a post about this sometime back right after Ed and I put the brakes on my car. The rotor in addition to the spacer brought the rear wheels out to where the fronts would have sat on the OE brakes. With the .200" extra from the rotor hat it should be close enough to work without problems.

 

Hmm, didn't realize that. Makes sense though.

Thanks for the info and education!

 

Oh yeah...rotor and caliper weights for you race guys.

13" C4 HD: 20#
12.75" C5: 19#

This 12.2" x 1.25" Wilwood rotor: 13#

That's 12-14# off the front in rotor difference.

Caliper weights:

C5 loaded (caliper, carrier, pads, guide pins): 10#
C4 loaded: 9#

Wilwood FSL with HPS pads: 7#

That's another 6# gone.

Ed

 

For those that may be interested, Ed started this project after I found him on this forum and contacted him about a setup for the front of my '88 American Sedan Camaro. Our brake rule just changed for 2006 and we are now allowed to run a setup like the one Ed has put together. Before, we had to use 1LE style brakes with the PBR caliper design but we were allowed to switch to any rotor/hat/hub combo as long as it was 12" or less. I was running stock 1LE rotors and C4 Vette GS calipers. These are the black calipers that are slightly beefier than the reg C4/1LE PBR.

We punish the 1LE brakes way beyond anything they were designed to do and the SCCA finally saw fit to change are brake package. In the past, I would have to put new rotors and pads on for each race weekend. I used GM Durastop rotors that lasted as long as anything at about $35 each and either PFC01 or Carbotech X11 pads on the front. The rears are the stock 1-piston setup. I use a lot of different pad compounds on the rear including cheap, stock pads sometimes. I have a cooling plate that I fabbed to go behind the roor with a duct outlet welded to it. This helped tremendously as far as brake fade but I still seem to wear out rotors and pads just as much - probably because I'm not afraid to use them harder now. I was planning to upgrade to a separate rotor/hat setup for next year until our rule changed.

I will definitely give Ed feedback on how this setup works on the track. I'm looking forward to a greatly reduced brake consumables budget that will hopefully pay for the new setup in a short amount of time.

-Jeff

 

Way to go Ed,

Perhaps I'll jump onto this one in a month or two. I got a clutch, UBE decoupled torque arm, and a Moser 12 bolt to pay for first.

One question I have is this: I have experienced poor braking performance from my 1LE brake package: Too much rear brake bias is the problem and I have severe wear on the rear rotors with virtually no wear on the front brakes at all. So I am very concerned with the issue of brake bias.

How are you addressing the variations in terms of different master cylinder / combo valve combinations, coupled with the difference in clamping force of the four piston versus the 1LE front calipers?

Is it standard practice in A sedan to substitute a proportioning valve in place of the combo valve in order to tailor brake bias?

Whatever happens, I want to fix my braking problems once and for all before hitting the NFME event at Indy this upcoming May.

 

We are allowed to add a in-car adjustable restrictor type proportioning valve to the rear line/brakes. I am using a wilwood unit right now that is pretty much set on full restriction. Even on full restriction (which doesn't restrict completely), some people still have brake hop issues. I've even seen AS cars with two of these in the rear line. A third-link setup usually cures the wheel hop and we can add more rear brake back in. That's my plan but I haven't come up with a good 3rd link setup yet. I'm using Dana 44 rear right now but I may go to a 9" soon (we're allowed to per the rules).

-Jeff

 

Jeff,

Is the GW track-link A-sedan legal? I would image that if you could properly tune that (or get a UE DCTA some how installed), that would really help the brake hop issues. hmm, I wonder if there is a way to change the dive geometry in the front, to help keep the rear wheels from unloading.

 

Yes, the Traclink would be legal. Do you think this would help with brake hop as much as a true third link? It may be worth a try. I guess we're kinda getting OT here but I appreciate the input.

-Jeff

 

It should be much better than a factory torque arm setup. You would probably need to crunch some numbers, and try to figure the instant centers with both a three link, and a the track link. For easy of install, and packaging, the tracklink would seem like an easier solution. The numbers and track time would be the only way to get a good comparison though.

I really like the UE peice, but I have not yet seen one fitted to a thidgen. I know there are several 4thgens in CMC and possibly even in AS, that are running the decoupled torque arm.

Might be a good move, to start this topic up in the suspension forum, instead of continuing to hi-jack this thread.

 

Agreed.

BTW, Ed, how are things coming?
-Jeff

 

I got back in town last night at midnight, I'll check on the finalized brackets tomorrow as well as the hubs. I hope to have it totally done next week, last week didn't allow much progress on it among other things.

Ed

 

Ed, do you know the weight of the stock brake discs and calipers in comparison. What is the unsprung weight difference compared to stock?

Many thanks!

 

Hi Ed,

Will your new Wilwood set-up work with Formula wheels? I am trying for a stock look on my '91 Formula street car. I am really curious and excited to hear about this as I race CMC, have been racing with a 3rd gen Firebird with the 12" Baer brakes set-up. I have never had any complaints about the braking or unusual wear with that set-up. I was planning an LS1 brake conversion for my '91 Formula, I think this changes my mind! What is the best way to keep updated on this kit?

I will agree with the comment that too much rear bias is a problem on the third gens. I also have a Wilwood proportioning valve that is usually dialed full out on the rears.
Another thing you can do is have really non-grippy but good wearing brake pads in the back. Some folks go as far as to grind off some of the brake pad material!

Hello Jeff from on of your CMC counterparts! I am also running a Dana 44, perhaps the only one in our series!

 

Julie. (ps- we met once at Calif Speedway) Its not the rear brakes thats the problem, its the rear roll center being too high. Lower it and you rear brakes will be much more usefull. I would more advise raising the front roll center via longer balljoint studs and then reshimming the coils to the existing ride height.

The stock weight of the entire front iron caliper factory setup (single piston 10.5 rotors) is about 40-41 lbs.

 

Good information. Thank you!

Okay, here's a dumb question from a suspension tech newbie:
How do you lower the rear roll center?

Thanks again!
-Jeff

 

not a dumb question- You do not have the provisions to lower it from the factory. If rules allow, you need to weld on the provisions. Here's my car. This is a Jegs unit that trust me is very very strong and user friendly in instrallation. make sure you weld it though- bolt on is scary.

Now when you lower the rear roll center, you will have to try and compensate for the added suspension roll leverage with about a 2mm larger rear swaybar and maybe even one click up on the rear rebound.

ps- this is a very slow 135rwhp V6 that has run a 2:09 on Calif Speedway roadcourse on street tires.

Dean

 

Hey Dean,

Nice to see you on TGO! I've been on here a lot lately with my '91 Formula project!

Thanks for the info...my brake hop problem was solved, I know some other 3rd CMCers that would like your great info here though!

I'll hopefully see you again at CA Speedway, this time I'll be piloting a 4th gen Trans-am CMC car! My 3rd gen CMC car "sniff" is for sale. That's why I got into the Formula project because I knew I'd miss it!

 

I'm not sure how the rear roll center is coming into play here. The part that effects the front/rear is the instant center. Changing the rear roll center would effect the rolling of the rear, in comparison to the roll in the front.

Maybe Dean just worded things funny. IMHO, the issue, is trying to balance the anti-squate and roll steer on these cars, with the braking feel. The brake bias isn't an issue, until you put descent brakes on, and sticky tires that allow you to brake that much harder. Doing that transfers weight to the front, thus making the amount of work that can be done by the rears less.

So the goal here, should be to optomize the suspension, so that you can have the rear brakes help you out, instead of just dialing down the bias so much, that they are no longer doing anything. By using a de-coupled torque arm, or changing the anti-dive properties of the front suspesion, you can do that. In theory, changing the LCA geometry, you could also get some help there, but doing that is at the expense of the AS, and forward traction.

 

John, The roll axis on these cars is much too incline towards the front from the factory. Under braking, that inclination increases and causes the rear tires to unload even more. Most people just try to reduce the rear brake bias not knowing what the real cause is.

the faster your car stops the more previlant this problem becomes counter acting its potential. You have to get your roll axis flat to have a fast car.

 

I agree the roll centers are off from the factory.

BUT, The force under braking is fore/aft, the for/aft instant centers, determine the dynamics under braking and acceleration. The roll centers (basicly the instant centers in front, and the point suspension rolls around (I know you know what they are, but I figure not everyone does)) detnermine dynamics under lateral foces. To reduce the wheel hop, you have to correct the right point. The problems is that the anti-squate here, cause brake hop. Just like screwing up the AS can cause wheel hop under acceration. We don't tell people to raise the roll center, when they get wheel hop under accelleration. We tell them to move their IC, so their AS goes up. You get brake hop when you have too much forward AS.

Under braking, you deal with the same forces, just negative numbers, so to say.

 

Rear brake hop and reverse AS are cause by using too short a torque arm. Rarise the front roll center or lower the rear and you can use a longer more stable tqarm for both acceleration and braking.

You need to start with whats wrong with the car 's design (inherit defects to start with) then make pruchase desicions and setup adjustments acordingly. You can not make one of these cars fast without lowering the rear or raising the front roll centers- then playing with the IC comes after that to fine tune things.

Thats why when you make a roll center adjustment it affects so many other things. Hard to just do that after the fact- it should be started with.

You casn get the same bite off the corner using a longer TQarm with a lower rear roll center without the wheelhop under braking.

 

I'm still not seeing how the roll centers effect for/aft tranfer and dynamics.

What force is acting on the roll center? The LCA's have no effect on the roll center. The part of the suspension that is being effected, never touches the roll center.

Maybe I am slow (I have never admited anything else), but I still fail to see how braking torque, and its effect on the vehicles dymamics, get effected by the height of the roll center.

 

Since no-one has showed up yet under suspension:

Only stock torque arms are legal in CMC.

 

Thanks for pointing that out Julie.

I will have to check back through my info at home, and find out what classes people were running them.

BTW, here is the rear suspension geometry for our cars.

 

John, The front roll center and the rear roll center are joined by an imaginary line. That line is called the roll axis. It is how the car pivots or rolls side to side.

However, how that roll axis comes into play for and aft is it is also the line that weuight tranfers along for and aft.

Its like having objects in the back of a truck bed. If the truck is a lowrider in the rear, when youtake off from a light even slowly the load will slide backwards easily. Now if the angle is raked forward then you can take off faster with less load shift. Same goes for braking, Its the angle that supports or allows weight tranfer along. Remeber, its not the angle of the body, its the angle of the imaginay line(roll axis) for and aft.

 

Wew are hijacking Ed's thread here but this is important for people to learn when doing brake changes also and how more front brake presure (larger front brakes) increases the braking problems associated with the bad roll axis.

this picture shows the roll axis inclination between the front and rear roll centers and the lower picture shows how the same car at same ride height rake (but higher roll axis rake) will jack in the rear under extreme braking forces.