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Lets talk about slotted rotors again


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21 replies to this topic

#1 WJM

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Posted 16 February 2005 - 02:27 PM

$200 for a full set of slotted rotors...8 slots front and 6 for the rear.

Or...$100 for either the front or the rear.

Who would be interested?

#2 spanky_pete

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Posted 16 February 2005 - 02:34 PM

$200 for a full set of slotted rotors...8 slots front and 6 for the rear.

Or...$100 for either the front or the rear.

Who would be interested?


Interested, yes. But unable to commit without getting a few other purchases out of the way. Any pics of the rotors?

#3 carfreak85

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Posted 16 February 2005 - 02:36 PM

Would we be able to get these done for the front rotors of EA81s?

#4 scrapdaddytatum

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Posted 16 February 2005 - 02:46 PM

ok im interested, for my wagon, better than brembo blanks.......let me know what you need from me

#5 Do It Sidewayz

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Posted 16 February 2005 - 02:48 PM

you do know that with Modern brake pad formulations slotted rotors actually offer worse braking performance.

the slots were originally designed to de-gas the pads, back when they had gassing problems with pads, and the gas formed a barrier between the pad and the rotor.

Now...you don't need the slots as pad gassing isn't a problem.

You will also create more heat with a slotted rotor.

You will stop quicker, cooler, and pads will last LOTS longer with a quality Blank rotor.

I'm not talking crappy rotors made in thailand or china. Brembo rotors are available for the EA82T cars. They are excellent rotors, and stop well.

If it's a bling factor....slotted rotors are ok.

If you actually want braking performance...just get good blanks.

#6 scrapdaddytatum

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Posted 16 February 2005 - 02:55 PM

really good point sideways, i agree totally, i didnt think before i posted, but the slots actually increase temps, to offer faster warmup and better pad adhesion, but we do this on race cars, with cooling ducts and HUGE rotors where the outer edge has a tendency to be cooler than the inner edge, i have brembo blanks on my rx wagon, with real good pads that have the slot in the middle, this slot is the same as a slotted rotor and help gas escape without cooking the rotor, my brakes work great, get up on them and the feel and act the same as my slotted brombos and ebc pads on my impreza, i would have to agree that slotted rotors on a ea82 street car might be a bad idea, would look cool though, but leave the bling for the new gen cars

#7 avatar382

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Posted 16 February 2005 - 03:07 PM

Regardless, $200 is not a bad price.

I paid $150 for brembo sport slotted rotors for a Chevy Cavalier. Cavalier rotors are the same dimensionally, as an XT6.

Blank rear rotors were another $100...

#8 WJM

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Posted 16 February 2005 - 03:09 PM

Would we be able to get these done for the front rotors of EA81s?


Yes.

#9 nkx

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Posted 17 February 2005 - 02:09 AM

i thought slotted rotors were also supposed to add more 'bite' because the edge of the slot cut into the brakepad, thus increasing braking ability..?

#10 WJM

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Posted 17 February 2005 - 06:47 AM

My problem is that I get ALOT fo heat build up. How am i supposed to keep the rotor cool? I mean...i get it GLOWING RED all the time? I thought the slots were to help carry gases off so there was less fade....im thinking drilling helps in cooling AND gasses...

#11 Do It Sidewayz

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Posted 17 February 2005 - 08:18 AM

here's a good tech article that William from Williams Performance Friction posted on a local forum.

Rotor Information
Tech Article

I recomend solid blanks for Solo1 and regional racing.The slots serve as a cosmetic feature only.Slotted rotors increase your stopping distances because of the reduced surface area.

Think of the rotor as a tire.If you have grooves in the tire(TREAD) you reduce the surface area so they don't grip as well as a slick (No Tread).Quality blank rotors are best for competition.

People are going to respond to my FACTS, not my personal opinions about this matter by saying that slotts de- gas and or de- glase the pads.

Modern racing brake pads are made with non-organic materials that do not gas like the old days.Prior 1985.
In the old days brake pads were made with Formaldehyde, Cashew nut shell oil, Barytes, Lime, Zinc, Copper,Brass, lead,gum rubber,carbon black,graphite,Sulphur and Asbestos.

When this toxic mess was heated and pressed under extreme pressure(100 plus tonnes) in the presence of air ,only the outside skin of the thick brake pad would polymerize.The polymers in the compound have not cross linked fully.This is called a Unsaturated state that has free linkages which can join with other atoms and molecules to form a different product.To combat this problem in racing, the engineers created the slotted rotor to peel away the outer layer of the pad.The pads new layer would then Polymerize under the heat of the rotor and pressure of the caliper to keep the consistancy of the brake feel uniform.(NO FADE)

The modern day Racing brake pads are designed for total polymer saturation where the polymers cross-linking is fully complete after it leaves the press and you have a sound product.
No need for the slotts.

Re-cap
1985 and older brake pads- Unsaturated polymers which still has free linkages which can join with other atoms and molecules to form a different product than you intended.

Modern day racing pads-Are refered as Saturated polymers where the cross linking of atoms and molecules are totally complete.

Hope this answered all the questions about slotted rotors.

William
Williams Performance Friction




he doesn't talk much about cross-drilled... but really they are worse. If you are getting your rotors to the point where they are glowing red, then you will crack drilled rotors to hell in about 10 miles. The only drilled rotors which will stay together are those who have the holes CAST into the rotor....rotors that are drilled from blanks, do nothing but create stress risers at every hole and you will crack them...it's just a matter of time. I have actually seen cross-drilled rotors explode...NOT PRETTY!

I recall you were talking about doing a gb on Carbotech pads....if so, you are spending a good amount of cash on your pads, and i'm sure you'd like them to last longer than 1 track day...slotted rotors will do nothing but accellerate pad wear.

for what you are doing...the key is in the pads....and there is NO single pad out there that will achieve what you want. you really need 2 sets of pads...one set for the street and one for the track.

As far as cooling..you really only have 2 options...
1. brake ducting, install brake ducts which force cool air onto the calipers.
2. larger rotors....you are trying to slow down a 2700+ lb car, with 10 inch rotors....it's no easy task, a similarly weighted new car would come with much larger brakes and wheels. Larger rotors are the only real option as you physically have more material there which takes in more energy and disipates it better (heat)

If i was you, and you seriously had this problem....stock replacement crap isn't where i'd be looking...you need to look into an XT6 hub swap, and possibly upgrade to legacy turbo or impreza 2.5 RS brakes on those hubs when you do. You need to get away from the single piston caliper stuff that RX's have stock.

oh yeah....you shouldn't be using the brakes that much anyways....they just slow you down ;)

#12 WJM

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Posted 17 February 2005 - 10:09 AM

Ok, im staying solids and trying out some new pads.

#13 scrapdaddytatum

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Posted 17 February 2005 - 11:17 AM

i would conside a hub swap and doing wrx brakes, im thinking about this my self, i have a strut/hub setup from my 95 impreza and im just going to toss it on and see how well it fits, i dont want to give up my german 14" alloys but better braking would be good, mine grind under hard braking, but this is the pads, and im used to it, my race setup on my impreza does that too, brake ducting is a great idea, but my understanding is u run the ducts to the center of the rotor so the cool air can go out through the vents coolong rotor and pad, is this wrong, thats how my impreza and bmw are setup???

#14 JWX

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Posted 17 February 2005 - 01:04 PM

As far as cooling..you really only have 2 options...
1. brake ducting, install brake ducts which force cool air onto the calipers.

good idea here

2. larger rotors....you are trying to slow down a 2700+ lb car, with 10 inch rotors....it's no easy task, a similarly weighted new car would come with much larger brakes and wheels. Larger rotors are the only real option as you physically have more material there which takes in more energy and disipates it better (heat)

winnAr?


If i was you, and you seriously had this problem....stock replacement crap isn't where i'd be looking...you need to look into an XT6 hub swap, and possibly upgrade to legacy turbo or impreza 2.5 RS brakes on those hubs when you do. You need to get away from the single piston caliper stuff that RX's have stock.

I can vouch for this, he has SMOKED those rotors and pads before.

#15 WJM

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Posted 17 February 2005 - 01:16 PM

Smoked it not the right word....at the dragon, smoking and slightly dull red is accurate...lately its been ON FIRE and Rio Red glowing. :eek:

#16 Do It Sidewayz

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Posted 17 February 2005 - 01:34 PM

well..your obviously using the brakes too much then :)

look into bigger rotors man.

I'd think go with an XT6 hub swap, and use Legacy Turbo rotors and Calipers allround. The Legacy's used a nice 2 piston caliper (very similar to the WRX and RS) in the front, with nicely large vented rotors, and in the back they are actually a step above every other impreza as they used vented rotors back there also.

If you want a cheaper solution....Re plumb the rear brakes and get rid of the factory pressure regulator, and install a Willwood brake bias adjuster. You really need to get more brake bias to the rear of the car. Most people in the know, acknowledge that bringing the rear brakes much more bias is the KEY to stopping a car quickly.

The stock set-up is probably biassed to the front....prolly the front does around 70% of the braking..if you can get to the point where the rear brakes are doing like 40-50% of the work...you have just put alot less stress on the front brakes.

lets do some numbers here.....

Assuming a 75% front and 25% rear bias in stock form....and a 2700 lb car
the front brakes need to stop: 2700 lbs x 0.75 = 2025 lbs
the rear brakes need to stop: 2700 lbs x .25 = 625 lbs.

If you can get that to 60/40 or even 50/50....same 2700 lb car.
front brakes need to stop: 2700 lbs x .60 = 1620 lbs
rear brakes need to stop: 2700 lbs x .40 = 1080 lbs


The numbers and bias are probably way off...but you get the point.

if you can install a brake bias adjuster, and keep giving the back more bias until it start getting sketchy under brakes (rear wants to lock up). then you will take alot of load away from the front brakes, and cause less heat.

A brake bias adjuster is cheap...but you need to replumb the entire brake system (front and rear channel instead of criss-cross)

#17 Hodaka Rider

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Posted 17 February 2005 - 01:48 PM

You really need to get more brake bias to the rear of the car. Most people in the know, acknowledge that bringing the rear brakes much more bias is the KEY to stopping a car quickly.


DO NOT do this with stock supension. A hard stop with stock mushyworks will transfer much more weight to the front, causing the rears to lock up very easily. If you have stiffer springs/shocks, then no prob (that means you, WJM). Many Volkswagens have automatically adjusting bias via a valve that is connected to the rear torsion beam. When I lowered my first Jetta, braking got WAY better due to the combination of less weight transfer and more rear bias (lowering the car automatically gave it more rear bias). I don't think this could be adapted to the more independent rear susp. of a Soob, though.

#18 Do It Sidewayz

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Posted 17 February 2005 - 01:58 PM

actually...putting more bias to the rear would make the dive to the front less.

#19 WJM

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Posted 17 February 2005 - 01:58 PM

I see.

#20 PoorManzImpreza

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Posted 17 February 2005 - 11:40 PM

I'll just chime in here briefly..

My brother in law drives a '98 corolla GT has a 20valve 4a-ge not bad..I noticed that the rear discs are actually BIGGER in diameter than the front..when we put new brake bads on it we put TRD pads on the back and some semi metallic stuff on the front..car stops VERY well with almost zero forward squat..other toyotas with drums on the back squat horribly and some even lift in the rear..the lesson here is that more stopping power in the back causes less squat which in turn allows the rear discs to contribute more to stopping the car..for the power levels that some of us are making (read: Will) the stock brakes even with nice pads isn't really up to the task..we REALLY need bigger discs..I also HIGHLY recommend a bigger MC..I'm working on some custom rear discs and a modified front disc from another car..I'm aiming for a bolt on setup..as soon as it's done I'll post pics..Bigger is better than slotted..

#21 JWX

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Posted 18 February 2005 - 12:15 AM

wow......I was actualy kinda right about this. I've always said we needed more stoping power in the rear.

#22 Hodaka Rider

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Posted 18 February 2005 - 04:38 PM

actually...putting more bias to the rear would make the dive to the front less.

OK, I'm speaking from actual experience here. Maybe under easy to moderate braking rear bias will help, but I'm talking about HARD braking with stock suspension. Your rears WILL want to lock up easier.
We're talking about physics here. Weight transfers can be so violent that there is effectively very little weight holding the rear end of the car down. (we're talking about front engine, front- or all-wheel drive). Usually about 60% or more of the static weight of the vehicle is over the front end.
Figure in a hard theoretical stop of 1g. If the car weighs 2700 pounds, with 60% on the front, that means about 1080 pounds is biased to the rear. Depending on the center of gravity of the vehicle, we could see over half of that weight transfering to the front of the vehicle. That leaves only about 500 lbs over the rear. If you increase the braking force at the rear by say 10-20% on a car that would likely be close to locking up the rear at stock bias settings (which I know my Soob was), you are almost sure to have lockup at the rear. Not to mention other factors, like the fact you are taking that braking force away from the front brakes, thereby reducing their effectiveness, and the fact that with stock suspension, the front end WILL compress more (or more quickly) than with uprated springs and shocks, and the rear suspension WILL extend faster than with uprated shocks - which both add up to even more effective weight transfer.
ON THE OTHER HAND, if you lower the center of gravity by installing uprated springs/shocks (like I said at first), you WILL benefit by adding a little rear bias. Note also that most newer performance cars have a little more front bias than required, to avoid unstable handling under hard braking. Some older cars (some mid-eighties Chryslers, for example) were cursed by automotive testers for having too much rear braking bias, which lead to scary situations in 60-0 and 80-0 brake testing.

That all being said, you were right that in Will's situation, an adjustable bias would be good, because his car is modified and weight balances, center of gravity, and other factors have been changed. The diagonal braking circuits could also be changed, as their main purpose was for safer stopping if one of the brakes failed.




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