924Board.org

[RC]

The question is:
To drill or not to drill?

Are there any thoughts or data on the various advantages and disadvantages of cross drilled discs? Particularly referring to 931/924S/944 brakes although any generalizations should apply.

We could also discuss slotted, grooved rotors and those with cast rather than drilled holes, especially if there are any available for these cars. Different considerations for street, fast highway/twisting mountain roads, autoX and faster track applications would be helpful to many of us.

[morghen]

mine work much better than the stock ones...but the rims are always black from the brake dust.
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Supercharger and EFI kits
https://www.the924.com

[Raceboy]

There's no point. If you find drilled discs, you can buy them but no advantages other than looks. BTDT with both 944 and 951 brakes.
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'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
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[Vince Ponz]

I have slotted on mine.
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"Never let them see you sweat"
77.5 924 modified track car
79 931 Euro stock
88 924S SE
87 911 Targa stock

[gegge]

The question is if it is for show or go?

Drilled had got less area, less weight and will crack sooner or later.
Slotted are better when wet.

If you want less fade, get better pads, remove dust shields and duct cold air to the center of the rotors.
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Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

[Rich H]

I have spiral grooved discs on the Elise.

Problems with drilled disks is if they are concentricly drilled you can end up with ridges all round the disc and pads to match. also they unzip radially along the holes.

The spiral groves on mine were done by a mate in scotland, the spiral groves sweep the whole pad to keep them deglazed all the time and to give even wear on both the pads and discs.

The only problem I have is that soemtimes the pads rattle as the grooves move the pads in the caliper and they click-click-click-click
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

[924RACR]

Spiral grooves (or other such slots) are the only proven way to go, beneficial for the wet only. Drilled are bad, as mentioned.

I run totally stock rotors on my racecar, as per the rulebook; would slot them if I could, but not really a big deal anyway (rain races are few and far between).
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[RC]

Thanks for the replies guys.

Backs up the general consensus of interweb experts regarding dubious benefits along with likely eventual cracking.

So the 3 practical advantages of drilled discs is the bling factor, they look cool and they also look cool. Right......... The only real positive opinions came from manufacturers and/or sellers, with a vested interest, and a few ricers.

Have dismissed the drilled rotors and accept that there is some benefit using slotted ones, particularly in the wet. Although I haven`t searched far have only found Meyle ones with continuous overlapping grooves. Crossed those off when stated made in Brazil, for some obscure reason. Recall there was an ebay seller who offered his machined slotted Zimmerman rotors but has now vanished. May not be a bad thing?

Anyone know of a source of quality slotted discs?

Any valid problems with plain flat Zimmerman ones?

Thanks