mark kibort

its a technique that will allow some amazing differences in your stopping power. its using the lateral capability of the tires, to scrub off even MORE speed. since you want to turn anyway, why not!

no magic at all. the principle is simple. as you load the front tires with a lot more weight, they have more grip. you use this grip for more stopping power and the ability to turn in at a faster speed. those that dont do it, and use the school line of late apex, can be left in the dust around a hard braking turn like Lagunas front straight to the hairpin, coming down from 120 to 130mph.
works with pinner tires too! (actually required with the smaller tires! )

xschop

330mm Cayenne rotor = 24 lbs
282mm stock 928 rotor= 16 lbs

After all the crying, you guys still think the extra rotational weight is worth it?

slate blue

I have Cayenne rotors in storage, they are the 390 mm ones and I believe they use the more modern style hub that came out with the 996. So this is where you may get stuck. Otherwise you may have to make hubs or at least adapt them.

Personally I am just going to use a 2 piece disc. I do realize they aren't super cheap but I wont use that many of them. They have quite a lot of disc area. BTW 995 GT3 discs used to be cheap them Porsche changed the price. Something to be aware of.

Greg

xschop

I just got the hub/bearings disassembled but stiil have to press the wheel studs out at the shop. Does anyone know where I can get the stud specs so I know what diameter to drill the stud holes since they are knurled and pressed in?

I tried a BoxsterS rotor. It fits with the centering rings and the porsche 4-pots clear but a funky bracket has to be milled.

Also this '85 928 hub has 7mm more offset than the 87-up 944/968 hubs and I got ahead of myself, the O.D./ hub/rotor registration are the same 155mm to be exact and 71.6mm wheel hubcentric.

xschop

Besides the 28mm thick BoxsterS rotors, is there another 28-30mm thick Porsche rotor readily available somwhere between 300-318mm O.D.?

The various offsets are definitely workable as there is plenty of clearance between the caliper and upper and lower control arm for alot of different calipers.

slate blue

Why don't you look at Nascar rotors with a hat? They are plenty cheap and good.

Greg

mark kibort

why on earth would you think not? besides , the ones I pulled off are only 20lbs. (vs the 16lb 928 rotors), and that is 4lb differences, but lets say its the full 8lbs. thats 16lbs of rotational weight, very close to the center of the wheel. If it was on the tire, it would have the effect on acceleration of near 2x as if it was sitting in the car. on the rim diameter, only 1.4x, and then on the rotor, less than 1.2x. So, both rotors have an 8lb difference, or maybe 16lbs dfference, which is like 20lbs as if it was in the car. thats 2hp equivilant. Its very low on the CG so its not a effect on handling. AND, now you have a large mechanical advantage for braking, and much better heat control of the brake rotors and pads. (reduced fade, feel and force!)

So, yes, it is WAY way worth it. if it wasnt, all race cars would use very light rotors of small diamter. (and hint: they dont! )

mark kibort

the centers of a lot of VW tourareg or cayanne rotors are the 157.1 mm so they will work being hub centric. (porche S4, OBs, etc are all 157.1mm)
the smaller dimension (i.e. 75 to 85mm), is irrelevant as it isnt used to center anything. its basically just a window to the wheel bearings.

xschop

I've done enough brake swaps to know the larger dia/heavier rotor installed, the more high speed centrifugal affect on steering/handling, especially at 100+ where I like to be before my morning exit to work LOL. I like my cake and eat it too.
Other than that, the only other thing I see could be a problem is the sliding caliper will chatter more on an extended bracket with it's loose fit arm-pins. It may be o.k. as the pad area is quite substantial anyways at 117x74x50. I also mic'd the '85 piston to 53.95mm and looked over the piston edge to seal distance/relationship to see if it could take a perimeter cross-drill mod.....I wouldn't have a problem doing it to such a large dia. piston, probably 20ea 1/8" holes around the perimeter wil reduce alot of heat input into the caliper.

Also the 157.1mm inner rotor dim is interesting. Do the Touareg/Cayenne rotors center by 2ea set screws? if so what are those PCD?

mark kibort

you have done "enough" brake swaps? really , how many "tests" have you done??
You will NEVER be able to feel a few extra lbs on a small diameter rotor. its just too small of a change compared to what is actually spinning out there. we are talking 3-6lbs compared to 66lbs spinning. its only spinning in the 1000rpm range, so you are not talkng some massive rotational speed. ou talk about 100mph with your morning coffee? you dont make rapid sterring inputs to notice anything at these speeds unless you are on the race track or on a real bumpy, and undulating road. for a street car the extra mass will help your silly street tires, helping fight lock up and give you stability for errant steering inputs.

Ive been racing a long time now, have done MUCH more dramatic swaps of weight, namely 5lbs weight change on the tire swap. ( old hoosier vs steel belted toyos) . thats 5lbs on a 26" diameter vs a 13" or 12" diameter of a rotor. thats an effective change that is 2 to 4x more than what we (you) are talking about here. guess what? absolutely NO noticible difference. certainly, my racing on the track with these changes with very high speed , and rapid sterring inputs, will dwarf anything you can do getting on your expressway going to work.

again, if saving weight in this area was a good idea, do you think ONE race team would do it?? guess what not one in the world agrees with you. Why? because the UNDERSTAND what Im talking about here.

It really bugs me when people post complete BS . why dont you also post that your car "Feels" faster after you wash it too. could be true, but it isnt reality.

Now getting back to the mod (hate to lay into you there, but the weight stuff is pretty easy to calculate), yes, it seems all the porsche cayanne and touareg rotors follow the same 157.1 inner diamter for rotor centering. not that this is a huge problem if it wasnt the same and larger, (smaller obviously wounldnt work), but its the same. So, the only thing you need to do (optional) is drill a small hole in the rotor hat to match the stock set screw. it certainly doesnt need to be done.

what are you talking about when you speak of the '85 set up on the the other "spindle" thread? the S brakes? right? those pictures i copied here, are of the calipers were confusing. Were they off a 944 or rear brakes off an S4? LOoking at those picures however, it would seemed my adapter idea will need to take a curved shape to clear the roundness of the inside of the S caliper (single piston caliper)

and yes, the pads are very substantial. M3 drivers have been racing with these same sized calipers for years and with larger diameter rotors. not an issue in anyway. only gains, no downside. This will be a tremendous gain for a budget racer wanting racing brakes with no real cost to upgrade!

by the way, if you really want to get that "feel " back using heavier rotors, fill the tires with helium, as that will counteract the effect that you can feel.

xschop

You need to come drive on Oklahoma roads and you know exactly what I'm talking about LOL. 120mph exits over a sharp turn uphill curve no doubt. You are just another faceless soul behind a keyboard and I don't take offense nor do I offer any. Just getting real world info for my project. I've never seen anyone build billet hubs for the 928 and I'm on it, I just have everything here for a big brake swap/adpter mock-up. The other post of mine is for the spindle dims to make sure I got an early set. seems they are 76mm calipers and 104mm calipers. The 79-85 spindles are stronger than the 86-up and that's what I'm going to churn out billet hubs for.
#2 yes those are Porsche Brembo calps that I just happen to have on hand that I am rebuilding and they have 36mm and 38mm pistons and would be a great caliper upgrade for up to a 318mm rotor. They about the same length, but way more narrow than the 928 sliding caliper. If you stick on a 77mm offset rotor they would still clear everything. Doing this mock-up I discovered that it would be possible to run 6-pots if you wanted to get stupid stopping power.

mark kibort

I dont know what you are "feeling" but if you really want to comfirm your "feelings", go and do a test for me. put on some 3-5lb heavier tires and do your test. if you can feel 3-5lbs on the rotor, then if its on the tire, you will be out of control. . Like i said, I race our cars. i run between 50lb wheel packages and 45lb wheel packages all the time, running 100-130mph on the track, some bumpy some smooth. Are you talking the roads in OK are bumpy? thats a shock problem. . if you are talkin steering input, at 120mph, sorry, you dont get the transitions that you would need to have to "feel" 3-5lbs on a rotor. are you feeling a turn in problem at 120mph . hey, dont take my word for it, ask anyone that knows their stuff on the subject, besides me. com'mon, who are you trying to kid here?
no offence taken, as Im just speaking reality here. dont pollute the discussion, with assumptions that are very far off base. lets take it to another thread if you want to go any farther with talking about 5lbs being enough weight to not do an upgrade due to handing degredation. clearly, it is not, and to say that it is, based on your "feeling" and no track experience, is a diservice to the list. you can ask, but dont come off as if you know.
again, no offence, just trying to help out the 928 community with a mod that will be much better than stock for many reasons.

Now back to the mods. so your other post has an old brembo caliper, but where is it from. those are aluminum calipers too and not really designed for front brakes as heavy as our cars are. Why wouldnt you just get a set of S4 calipers. are you saying that the S4 calipers with a 69mm rotor thicknes will hit the suspension because they are too thick? why not just do what Im suggesting? you feel a need for the 4 piston calipers? surely, they will be better and give better feel and wear characteristics, especially with a near GTS sized rotor (318mm rotor as you mention)
Is there a problem of using a billet hub as far as strength vs the iron that is stock on our cars. Interesting idea, but what are you trying to do, just mold out the offests for your new calipers? if that is the only reason, why not just find some used S4 spindles and job done? then you have the ability to do what I have done. use GTS /965T rotors 322mm and stock S4 calipers. or heck, just design it for the 330mm rotors from the cayanne.


Mark

xschop

No offense taken. Actually appreciate your real world imput. Yes, the roads are jacked up here in Oklahoma. I never argued, but asked about rotor weight as I have built kits for many bikes and a few cars, hot rods, especially my own and I always felt the extra rotational weight in the high speed steering only. From 80-130mph acceleration is where I notice the extra weight in my V8 swapped 944 with the BoxsterS Rotors, maybe it was always there in my other 944's, just never noticed because I didn't have the awesome acceleration that I do now. Like I said my goal is building 7x strength hubs for the 9 series cars and I just happen to have a harddrive full of caliper, rotor specs over the years and thought I would offer some help in getting better brakes on the 928 as well. I drove a well maintained 86 928 a couple years ago and the brakes were lacking IMO. The story of this thread is CHEAP rotor upgrade. Everything comes with a price. Happy new year, xschop

xschop

#2 you will have problem with the 928 caliper inner radius matching the radius of a 330mm rotor. Trim the cast steel outter caliper bridges and you are on your own.....some real world experience for you. Not trying to **** on your parade either, it will have some pad overhang on the outter perimeter.

mark kibort

I think its great you are posting some ideas here and are able to buid some replacement elements, like a spindle.

BUT, Im keeping it real in areas of expected performance. you post in this response that you notice the extra weight from 80 to 130mph?? well that is really where you would NOT notice it. this is the one area where the physics is pretty straight forward. take the interia value and plug it into the formula. because the rate of acceleration is so slow at the high speeds, the effects are minimal. its the same reason dynos use rolling dynos to factor out inertial values of wheels and tires. suspension action is an entirely different beast, but still we are talking about sterring inputs at high speed that are very slow compared to driving a bumpy mountain road at the limit at 40mph. Still, we are talking about effects much much less than a change of tire weight available for your car.

Now, as far as the fitting of the single piston calipers. yes, I imagine we need to hog out the edges to fit the much flatter circumference. we did this with the S4 calipers, so its not going to be a big deal for the S calipers, unless we are going to dig into the caliper fluild reservior.

the padover lap is not a problem we have the same pads (S4) ,and pad shape as the ferrari, yet 350mm vs 304mm rotors . its all in the set up. you want the outer center edge of the pad to meet the edge of the rotor. if it curves in a few mm, thats not a big deal or an issue at all.