YOU MUST DRILL THE HOLE SO THAT YOU DO NOT DESRUPT THE BALANCE.
CHEAPER TO BUY THEM. AND SAFER!!!
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Agree with Dwight. Saw this done once and was a disaster. Guy tried to balance them by measuring between holes. Had to buy new ones plus a few other things.
Cobra Make, Engine: West Coast Cobra weber fuel injected 557 C.I.. 800H.P 760LBS. TQ. Magnum T56
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DRILLING ROTORS 101
I HAVE HAD MY ROTORS DRILLED AND BEVELED AT A LOCAL MACHINE SHOP BY A GUY THAT KNOWS HOW TO DO IT CORRECTLY.
1. MAKE SURE AND DRILL BETWEEN COOLING FINS (IF SOME ARE DRILLED THROUGH THE FINS AND SOME ARE NOT, THERE GOES THE BALANCING!)
2. MAKE SURE THEY ARE EVENLY SPACED APART THROUGHOUT THE ROTOR.
3. MAKE SURE THEY ARE THE SAME DISTANCE FROM THE OUTER EDGE!
4. IF YOU ARE GOING TO BEVEL THE HOLES MAKE SURE YOUR BEVEL HAS A STOP SO THEY ARE ALL CONSISTANTLY BEVELED. (IF NOT THERE GOES THE BALANCING!)
5 USE A GOOD CENTER PUNCH AND A PILOT BIT SO HOLES DONT WALK.
IF YOU ARE COMPETENT ENOUGH TO FOLLOW THESE GUIDELINES IS I HAVE , YOU WILL SUCCEED. IF NOT "THERE GOES THE BALANCING)
GOOD LUCK!
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WHEN YOU HAVE MORE HORSEPOWER THAN YOU NEED ITS STILL NOT ENOUGH!!!!!!!
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It can only be done if you have access to the correct machinery, specifically a CNC vertical mill, or a mill with a rotary table. NOT A DRILL PRESS. The setup is involved and it is very time consuming. The opportunity for error is great and the ultimate result is the compromise in strength & reliability (IE:safety) of the finished. To do this correctly (holes) there is a formula that takes into account the thickness of the rotor, the width of the friction area vs the diameter of the holes used on a specific rotor. (how much material is removed). I chose to do slots in mine.
Attached is a picture of the rotors that I modified by the above process. Each rotor took about hour once the setup was done.
Slotted rotors are supposed to be the most efficient under heavy braking and heat generating conditions. I don't have holes or slots in mine, but I have seen some NASCAR rotors they use on the short tracks where they get red hot and they had slots. Unless you are doing a lot of really heavy braking, I think their main purpose is to look cool. Also from the NASCAR garage shows, they never use the same ones twice as the heat tends to warp them and cause problems. They are also used with the high temp. brake pads that won't work on the street. Some of the guys here put them on their cars and they just drive the cars on the street and put them in shows. They like to point out their Racing Rotors at the shows.
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Drilled holes and make rotors lighter all right, but they also introduce stress risers at every hole. What happens, then, if a rotor cracks, a section breaks out causing disaterous results. This happened to one of my late model stock cars, ending the race and causing a lot of damage. We drilled rotors before they were available from the manufactures. Braking definately improved.
What do drilled holes really do? Some ventilation is provided, but they allow gassing between the pad and rotor escape under extreme braking, reducing brake fade. Grooving accomplishes the same thing, but drilling takes it another step.
Drilling is not necessary unless you'll be subjecting your car to repeated heavy braking such as would be found under race conditions on a road course. Otherwise, they are to make your car look "cool".
If you drill your rotors, don't forget to chamfer the holes. Otherwise the rotor will act like a cheese grater working against the pads. You'll also have to have an accurate pattern laid out before drilling, then the rotors balanced as suggested. All things considered: If you want drilled rotors, buy them.
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"If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough HORSEPOWER." Mark Donohue
Some rotors are only dimpled instead of drilled all the way through...I believe this reduces the risk of cracks. As far as looks go...who can see them with your knockoffs on?
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Drilling was a great way to cure a problem that no longer exists.
IS ANYONE HERE USING OEM PADS FROM 1965? I didn't think so. Your all using modern pads which are matched to your driving habits (street, race) which won't have the gasing problems that old pads had.
If you *have* to have holes, have them cast in, NOT drilled. Otherwise, slotted. Which isn't really necessary except for the Bling Bling factor.
-steve in nj-
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For reasons stated above, I would buy rotors drilled or slotted, rather than try it myself.
I'm considering the drilled (and chamfered), or slotted approach, but for an entirely different reason. Driving in the rain. When stopping on a wet road, water on wet rotors and pads need to escape as a liquid or vapor before the pads can grip effectively. My thought would be that a slotted or drilled rotor would allow this transition from wet (no friction) to dry (friction) to occur more rapidly, allowing the car to stop more quickly. Any merit to this? Your thoughts.
Some motorcycles, BMW's, and Porsche's have drilled rotors so the idea has some merit for high performance street driving.
Some modern pads still gas and some don't, such as carbon$$$. But even if a pad gasses, grooving should vent it.
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Tom
"If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough HORSEPOWER." Mark Donohue
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Don't drill your own rotors. If you want them drilled, just buy them that way.
There are only two advantages to drilled rotors and not all of them have both. One is the vent the hot gas and the other is weight. All that rotating mass takes energy to stop and start. Mass is a double edge sword because less mass equals higher rotor temperatures all else being equal. I don't beleive you will find any help with the water issue here. Try light pressure on the peddle when driving through puddles or perhaps residual pressure valves would provide some releif so long as the pad stays in contact with the rotors. Although I am not sure the latter will have any affect. If you want the gas benefits of drilled rotors you can achieve the same results by slotting the pads or rotors.
Rick
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I will not touch the drilling or slotting question... however, be aware that a drilled or slotted rotor is not turnable. In other words, if it warps or needs resurfacing, they tend to be a throw away item. The holes or slotts just beat the daylights out of the lathe cutters. You may want to check into that aspect before you make your decision as to which way to go.
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Check with BAER and Wildwood, either one of them highly recommend AGAINST drilled rotors ....period. Heat build up is tremendous, and we've tried them both by the way. One of my original DV's used professionally drilled rotors, half way through the race the brakes were gone and the car started pulling a different direction everytime the brakes were applied.
Pulled the wheels and "every" hole had stress cracks leading from all the edges! We have since gone to "grooved" rotors on all our cars that even drive by a track, let alone get on one!
Drilled rotors are for appearance reasons only.
Not for performance use.
The pads that are avail today dont expell the gases they used to.
They are prone to stress cracks at each hole. They are more prone to warpage. They have to be surfaced more frequently, and go through pads more often.
They look good , and provide better wet braking.
(how often do you drive in the rain)
But all the other cons outweigh the pros.
If you must do something , consider having them slotted.
Use as big as a rotor you can fit.
Dont take my word for it, do more research on your own .
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After all the posts and research I have decided not to spend my hard earned money on drilled or slotted rotors. I will use my money elsewhere.....Thanks for all the informative input.
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