Brake rotor comparison lesson

[Techno Duck]

New parts came in the mail and laughed when i compared the sizes of the 928GTS 'Big Blacks', stock 951 and stock 944 rotors. I knew the big blacks were bigger, but i didnt think it would be THAT much bigger...

The 928GTS rotor is 12.68'' diameter and 1.26'' thick.
Stock 951 rotor is 11.73'' and 1.10'' thick.
I didnt even bother to measure the stock n/a rotor..





From left to right, FrozenRotors slotted cryo treated 928GTS rotor, ATE slotted 951 rotor and stock n/a rotor

[nynor]

what does it take to convert to the 928gts rotors and calipers?

[TNT25169]

So the turbo brakes and rotors on a N/A wasn't enough stopping power? You're going to need more rubber up front...

[Techno Duck]

nynor, you need the calipers, rotors, pads and if using your standard 951 spindles adapters to fit the radial mount calipers. You can source the correct radial mount M030 spindles, but they are expensive and hard to come by. You will probably also need ABS... .

TNT, the brakes are for the 951. I have enough trouble not locking up the front wheels on my n/a with the Brembo's. I will say the stopping power with 225 width r-compounds on the front is absolutely unreal.

[VINMAN]

Those look like the rotors off of my dually!!

[flash968]

more stopping is good, but all that extra mass is what prevents me from doing it - it kills quite a bit of power and initially takes more to stop it too - the trade-off is a real problem - same thing with the big reds

i am looking to get aluminum hat rotors in the OEM size for my car - i should lose 2 lbs per rotor, which is an effective total of 3 hp, and pick up better braking and a more active suspension to boot

changing the brake bias valve in my car made a HUGE improvement in the balance - i added some rear braking and now she drops down nice and flat

[lousailor]

Flash,
Where did you get the brake bias valve? Is it adjustable? Thanks

[flash968]

not adjustable - there are a number of them, each having a different front/rear ratio

stock for me was the 5/18 - i am now using the 5/33 and i got it from sunset imports, but pelican probably carries it - it is a porsche part

keep in mind that my car is a 968 - not sure what the crossover applications are for earlier cars

the ratios and part numbers are:

5/18bar 951 355 305 01
5/33bar 928 355 305 01
5/45bar 964 355 305 00
5/55bar 930 355 305 01
5/60bar 965 355 305 01

[d.a.autry]

Keep in mind that you can get adjustable proportioning valves

[Beetspeed]

Originally Posted by flash968

i am looking to get aluminum hat rotors in the OEM size for my car -

Did you find any?
Any-one know who makes these?

Tnx,
Walter

[lousailor]

I know Brembo makes a great after market set, but I imagine you would have to go to a "Big Brake" set-up. I don't think they make stock size versions for the 944.

[looneybin]

anybody here installed the Wilwood 4 piston front caliper for the 944 NA?
Looks like a decent setup, too bad it's only for the fronts & not all 4

[lousailor]

Actually for any sport driving, you really only need to increase braking at the front. That's why when they went to the bigger brembo 4 piston set-up for turbo, they used a proportioning valve on the rears. Under hard braking the car's weight shifts forward, and if the same pressure is applied to the same size brake set-up front and rear, the rears will lock up (very bad coming into a curve).

[flash968]

i am finding exactly the opposite to be the case, as are most racers

adding rear brake has been the key to balancing out the car, and getting through the turn faster - i changed the proportioning valve to one with more rear bias and significantly improved things - i'd add a touch more, back there, but i would be right on the edge in the wrong situation, so i'll probably leave it - a quick measurement of rotor and caliper temps will show this

making the fronts bigger will stop the car faster, but all at the front, and it will increase the front transfer - the idea is to prevent a lot of the weight transfer to the front, keeping it on the traction wheels more

[Beetspeed]

Flash, your giving away your edge on the track with this info!
(but I agree; its even more true in a rear engined car is my experience...)

[flash968]

lol - no fear of any "edge" lost - i'm rusty as an old gate - nearly 20 years off will do that to you - just now getting back onto the track, with a LONG way to go to getting back into form - i have to nearly start over, as this car is nearly twice as heavy and about half as fast as what i used to drive

still fun though

[xupkid2]

I have an '88 NA with no ABS and am interesting in the brake bias adjustments you are talking about. Is this part only for ABS units? I run Hawk HT-10 pads with cryo rotors up front and they work well but I have had the same back brake pads for 2 years now and I usally do 25 track days a year. Im interested in adding some back brake to the setup to help balance things out a bit. Please let me know if I can do the adjustment with the parts you mentioned and if the part #'s previously listed with work.

Thanks
Brian

[Techno Duck]

The bias valves will work on cars without ABS. However im not sure what kind of effect they will have with the different size single piston calipers. I know the 944S came with a 5/33 valve.

[ae1969]

Did you happen to weight them?

Curious what the difference is?

[Techno Duck]

I did not weigh them. The caliper weight between the 951S caliper and the GTS (Big Black) is negligible. Lets just say the weight difference between the stock 951 rotor and the GTS rotor is significant..and it makes the stock 951 rotor look pathetic .

These brakes are truely overkill for most applications, unless of course your car will likely be spending the rest of its life on a race track. The car might not respond as 'quickly' as it does normally by increased unsprung weight and rotational mass, but i like knowing i have more braking power on tap than i should ever need . Im going to be running these with the 2pc 968 brake cooling scoops, so this should be more than enough. The dust shields are long gone. I hopefully will never have to go with the foglight type ducting.