RacePro Engineering

We are all well aware of the current trend to increase braking leverage by using larger and larger diameter rotors (and calipers). Unfortunately, this strategy usually requires the use of larger and larger diameter wheels (and tires). Very soon, unsprung weight has gone off the chart.
We are prepping a C4, and have done the "standard" things so far: *Replaced stock rotors with ventilated and slotted. *Replaced brake lines with stainless. *Using ATE Blue racing fluid. *Using Hawk "blue" pads all around. *Added cold air ducting from the spoiler area.

Now to my questions:
Have any road racers found satisfactory ways to DRAMATICALLY increase braking force while retaining the stock size diameter rotors? Additional master cylinders? Brake proportioning valves? Are there better calipers (more plungers, like Brembo), which do not require larger rotors?
And if larger rotors are an absolute MUST, then are there 15"x 11" or 16" x 11" wheels which will clear the rotor/caliper assembly better than the stock 7" backspace variety?

Any informed insight will be appreciated.
Ed LoPresti

96LT1

First thing would be to know a little more about what year C4 you are working on and what size rotor. 84-87 all had 12" rotors, 88-95 had a RPO - J55 that was a 13" rotor. J55 was standard in 96.

First thing most people do with 12" rotors is to upgrade to the J55 rotors and calipers. (Some OEM Enkei 16" wheels will fit over the 13" J55 rotors) Next install a bias spring or in-car proportioning valve.

I'm not up on the Hawk pads but if you are serious about braking, I would think you would be looking at something like the DTC-70s and 60s.

davidfarmer

Cooling, cooling, cooling first. You need SEALED backing plates with lots of airflow. If you cant keep them cool, then larger rotors are the next step. Any good racing setup will have aluminum hats with steel friction plates, so both rotating inertia as well as unsprung mass really doesn't change that much.

If you keep the piston area similar to stock, you can keep the OEM master cylinder. A lot of aftermarket calipers really screw up bias, so make sure you keep that in mind.

Doug Rippie raced a lot of C4's back in the day, and I would get in touch with them.

Sidney004

I use DRM Stainless Steel pistons on the J55's, it is a worthwhile addition. The greater coefficient of friction offered by the pad choices would increase braking force over the Hawk Blues. PFC 001's have a high CF.

AUTO_X_AL

I run the 96 GS brakes with the S.S. lines and the DRM stainless pistons. We did find that all of our stock 16'' wheels would not clear the larger brakes. Good brake cooling is equally important. With two drivers we have yet to have any issues. I would go after the GS calipers due to the fact that they are a bit stronger than the standard J55 brakes. The GS calipers dont deflect as much. So far we have used the HT-10 hawks and they have worked pretty well. Side benefit of good cooling is cleaner front wheels as well!!

STEVEN13

Hi,

Car 1992.

GS calipers here also with SS lines, DRM bias spring, and cooling ducts. I have run with Hawk (blue) and had no problems. Now I am using PFCs 01s and 97s.

This set-up works for me with a stock LT1 for 20+/- minute sessions at Pocono North and Lime Rock (Only tracks I run).

Steve

XPC5R

High coeficient pads will help (there are some higher than blues) I switched from wilwoood E's (street style) to H's - cold cf went from around .38 to almost .5 - dramatic difference in power.

Other options, calipers with larger pistons (more square inches to exert brake pressure) or smaller master cylinder (less square inches, higher pounds per square inch). Either options will add some pedal travel, but you will get more force at the rotor.

RacePro Engineering

Gentlemen,

Thank you all for the most helpful suggestions!

96LT1 - The project car is a 1987, bone-stock coupe, which we are bringing along very G R A D U A L L Y. I am unfamiliar with the DTC - 70s or 60s which you mention. Where can I find out more about these?
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David - "Cooling, cooling, cooling . . ." Of course: simple concept, yet so difficult to achieve. Do you know off-hand a good manufacturer offering the aluminum hat/steel friction combination in a 12" rotor / reasonable-size-caliper ? I have spoken several times with Randy Rippie at DRM, and have purchased their "trick" proportioning spring. Their standard solution was to simply "go larger."
Still on the subject of cooling, when we prep 911es for the IT and "stock" racing classes, we use an aramid fiber (carbon) brake pad, which tends to INSULATE the heat of the rotor from the caliper (or at least not transfer as much!) Are there any such pads available for the "stock" early C4 calipers?
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Sidney and Auto_X_Al - By consensus, Rippie stainless pistons seem to be the "way to go". Any idea what makes them superior to the stock pistons?
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Steven - It looks like we are out-voted on the Hawk Blues, but just out of curiosity, why did you switch to Performance Friction?
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BPC5R - Good points about the mechanics of the system. Right now, we are suffering from OVERHEATING (fade), AND mechanical inadequacy (squeeze on the rotor). I suppose we should solve one first (logically, fade), then work on the other.

One more general question if I may: To achieve accurate adjustment of brake bias, can we install a proportioning valve (beside the stock master cylinder), or will we need an additional MC with a balance bar attached to the pedal?

Thanks again for all the great input.
Ed

96LT1

Information about the different compounds from Hawk is available at http://www.hawkperformance.com/motor...unds/index.php

Enkei was one of the manufactures/suppliers of the OEM from 84-87. Enkei wheels were in both a 8.5" and a 9.5" wheel depending on the suspension option. The 9.5" wheels fit over the J55/GS calipers.

Stainless steel pistons conduct less heat than the OEM pistons. {Under extreme temps the OEM pistons are just large heat sinks}

ghoffman

I agree that the SS pistons from DRM are a really good, almost mandatory mod. The thermal conductivity of SS is only 10% that of aluminum (112 BTU-in/hr-ft²-°F versus 1160). Titanium is even better (46.5 BTU-in/hr-ft²-°F) and 1/2 the mass of SS. It significantly reduces the heat transfer into the brake fluid. You will be amazed when you compare rotor weights, they vary alot from brand to brand for a given size. Alot of the weight in stock type rotors is in areas that do not help, like the flange. The weight does not help anything, increases the rotating moment of inertia that needs to stop itself in addition to the car, and increases unsprung weight that reduces the tires' contact with the ground (unless the track is billiard table smooth).
Also keep in mind where you are going to run. At Lime Rock, you can go faster with lightweight brakes but at the Glen or NHIS, you want all brake you can get.
BTW, if anyone is interested, the above properties are from www.matweb.com and you can search and compare almost any property of any material.

WNDOPDLR

I had similar brake fade problems when I started with my C4. Had stock C4 rotors and calipers, PFC pads, and no ducting. I eventually wound up with the C5 front rotors and calipers, Wilwood H pads and some home made very crude ducting. I also run the Rippie bias spring.

My barometer for brake performance is Carolinas Motorsports Park which is a track that is hard on brakes for a heavy car. No more brake fade. The Wilwood's eat up rotors, but rotors are relatively cheap compared to C4 parts and easily changed.

MistressMotorsports

Circle track and vintage racers are usually limited to 15 inch wheel diameters and have some awesome brakes. I would think you could get an 11.5 or 12 by 1.25 inch rotor and a decent four piston caliper for not too much money. I ran my vintage 240Z with 11 inch rotors, Outlaw calipers (Wilwood copies), custom mounts for the calipers, and aluminum hats for the rotors for about $1k. Those fit inside 14 inch wheels. I am of the opionion that you can add bandaids all you want to the stock setup (I had a 93 C4 where I did just that - Rippie spring, ducts, ss pistons, etc.) and found I still faded brakes, cooked rotors regularly, etc. I even tried a kit that put two stock calipers on the front with a stock rotor. However, there was nothing that performed as well as going aftermarket. Of course I was running 17 inch wheels, which were stock on my car, so the availability of Vette specific kits was better. There must be someone out there with a template for a caliper mount to use Wilwood Superlights or similar on a C4.

STEVEN13

I got a set cheap and just continued to use them.

Steven

AUTO_X_AL

I found that the 12'' rotors are about 33% lighter than the GS system. 14lbs as opposed to 21 lbs. I know I have heard alot of people say the J55/GS brakes will fit with the 16'' wheels. For one reason or another mine will not. Our car is an 86 Z-51 with the bigger wheels. I am not saying they wont just not on my car. The early C4 brake pad selection is alot more limited as fr as compunds go. We were running the HP+ hawks I believe before we went to the GS update and started with the HT-10. The DTC-70's will be next once I wear out the 10's. Alot of people really like the 70's. It seems to me that alot of people really have good luck with carbotech's price,selection,and performance. Mention Chris Ingle and get a discount to boot. As far as the cooling goes we route a hose right to the caliper to keep it cool and we have not had any issues but good fluid and upkeep is imperative. Mid america has a good duct setup but you do need to get some beeter hose to attach to it if you run really hard.

AUTO_X_AL

If you are having additional issues like having the Brake pedal get hard and raise up, C4's seem to be pretty notorious for destroying the diaphragm inside the plastic booster. Changing that for the first time is a pain but it's really not that bad(after 4 times I can do it under an hour now ). I would make a heat shield around the booster about 30% of the diameter(from 5 o'clock to 9 o'clock If you look straight at it) and try to get a steel replacement if you do have to change it. If you can find a lifetime warranty like from autozone it will make things cheaper down the road.

The GS upgrade will really make driving alot more predictable and enjoyable as long as you dont mind the additional unsprung weight. It's worth it IMHO. Good Luck!

Al

ghoffman

Yep, I have it.

96LT1

Just to make sure...

A number of places have the kit/adapter to mount the Wilwoods to the later (89-96) C4s. It is the earlier (84-87/88) C4s that I haven't been able to find an adapter for.

ghoffman

That is true, we have the 88 and up listed in the Wilwood catalog, but not earlier. They changed the uprights in 88. If you want we could make adapters for the 84-87 with the Wilwood SL6R caliper(like we did here for the C6 with the PFC zR33 calipers). We FEM analize them as well before we cut metal.


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Gary Hoffman
Hardbarusa.com
603-682-8073

Bill Dearborn

Ed,
Good to see your post. As I mentioned in our phone call there are a bunch of people here that can help.

I upgraded my 86 to a set of J55 calipers after finding the 12 inch stock system wouldn't cut it at the Glen. I was able to buy a set of 4 16 x 9.5 Enkei's which I put the R compound tires on and I ran my Gatorbacks on the stock 16 x 8.5 wheels that came on the car. All fit fine. If your car has the Z51 or Z52 options it should have the Enkei's since the 87 Z51 and Z52 options came with Enkei's. In a call with Dick Guldstrand I found out that some of the earlier non Enkei 16 x 9.5 wheels would fit over the calipers and bought a set of 5 from a wrecking yard. Two actually turned out to be Enkei's, 3 turned out to be from an 84 and I found I could get 2 of the 84s to fit over the calipers by filing the corner of the caliper by a couple of millimeters. The 3rd wheel had so much casting flash inside I would have had to file off a large part of the caliper corner.

Dick Guldstrand also recommended going with a larger Master Cylinder than I had in the 86. The reason being the 86 had a single reservoir and was designed to work with the smaller calipers of the early cars Vs the 88 and later cars having dual reservoir master cylinders that were designed to work with the larger calipers. I found that my 86 master worked fine with the upgraded brakes.

On the track I used to use PFC 83 compound in the front and 80 compound in the rear.

I also ran cooling hoses to the brakes which worked quite well. If you have Dante give me a call I can show him how to run some brake cooling lines from the front spoiler. Some racing brake hose, a 3 inch hole saw and a wire tie kit from Home Depot and you will be in business.

After the brake upgrade I went from running out of brake after 3 laps of the Glen to never having a problem. The top speed of the early C4s going up the back straight is about 125 for a stock engine in 4th gear (that is why I bought a 97 as soon as they came out) so you can get by with the setup I ran until the engine gets upgraded.

Another brake upgrade option may be to go with the C5 brakes. One of our club members recently acquired an 89 and upgraded to the C5 brakes. He was running it at the Glen with me this week and was using a set of Hawk Blues that I gave him and he really liked the brake feel.

As for brake pads there are so many its hard to know which to run. I found the Hawk Blues to have a lot more torque than the PFC 01s and they required an extremely light touch on the brake pedal to keep from overbraking the car. The 01s can run several hundred degrees hotter but require more pedal force to generate the same amount of torque.

I forgot to tell the guy who bought the 89 about the power steering reservoir problem the C4s had and when he went to the Glen in June he melted the reservoir and spilled power steering fluid all over the track and the car. He was able to get some Marine patch that glued it back together again and bought a spare just in case for this week. There used to be a vendor who sold a stainless reservoir for the C4s and that prevented the problem. Somebody on the forum may remember who the vendor was and whether or not the product is still available.

By the way we are going to have another multiple event autocross at Lafayette on October 14th and 15th. There will be a total of 10 events with at least 2 runs per event with 2 laps of the course per run. Should be a blast. We are planning on having a Steak and Bake after the last run on Saturday. Should be a lot of fun.

Bill

RacePro Engineering

Hello, Bill,

Naturally, I would rather converse on the telephone than use this rather "formal" medium. But just like our phone conversations, I am writing as fast as I can, and you are still delivering more useful information than I can digest in a single sitting!

I wish I had known you were at the track recently - I would have come to buy you a cup of coffee and watch the running. Dante and I are going to be up there next Wednesday & Thursday doing some testing. AT 125 on the back straight, I had better bring a book to read! I shall pass along to Dante your most generous offer.

Those of us who live in the area know that mid-October in Syracuse can present "iiffy" weather. However, if the snow isn't falling by then, we would encourage anyone who has not experienced it to try the high-speed solo event at Lafayette! That track has it all: hairpins, dog-legs, increasing radius, decreasing radius, surface changes, relatively long straights, full-throttle excelleration, hold-on-to-your-pants braking, AND severe elevation changes! Evey lap is a complete high-performance driving course! We are planning on it.

Rather than steal Forum space, I'll give you a call after our test days next week.

Ed