Rotors! Drilled, Slotted or Both which is best?

[ol_skl_jp]

I want to fit disc breaks in the rear of a 72' 240. Couldn't find alot of options in OZ ebay, so went on the US site and nearly creamed my pants on the amount of stuff they have over there for the Z (roughly 1200 items most are parts).

 

Anyway i m looking at some rotors, the guy assumed i wanted slooted only because im in Australia

"since you're in australia i am assuming you wanted slotted only?" I didnt understand this, could some one help me out.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=180218660310&ssPageName=ADME:X:RTQ:MOTORS:1123

theres the link. If anyone is interested shipping to Oz is 269USD

Is it a worthy investment?

Also which is better? (the whole point of this thread)

[Zedman240®]

Slotted is probably the only way to go, cross drilling is not the best for a few points. Removing material from the disc makes it less able to absorb and radiate the heat generated, and cracks are more prone to start from the drilled holes. If you are just driving around on the street, don't bother with anything, but for circuit work or similar, slotting should be fine. For a rear conversion, just use the brakes from a R31 Skyline on the rear. Easy to fit and cheap and plentiful!

[ol_skl_jp]

do the r31 rotors bolt straight on?

[tattoo_ink]

ive got those dba cross drilled /slotted rotors all round on my r31 and they suck ! 

already got lil stress fractures starting from the holes to the outer edge after 6 months so their going in the bin !

and i have been trying not not give them a hard time but i just put a modified rb30et in and they gota go real soon !

[sco_aus]

Although I agree that cross drilled arnt a good way to go unless made by a good manufacturer like Wilwood etc, the rear brakes would not get anywhere near as hot as the front and I wouldnt have thought it would be a risk of cracks etc from having cross drilled. I can see advantages from both perspectives, but for the front, definately not.  I would rather spend the money on getting vented disks and appropriate callipers.

[Zedman240®]

Ol_skl_jp, yeah, the R31 conversion is almost a bolt on exercise. The only hard work is to get the original Skyline caliper mounting bracket bored out and holes re-drilled to match the Zed rear hub. I've worked out a way to hook up the habdbrake cable as well with the calipers in the 3 o"clock position. Some people mount them in the 12 o"clock posi but it just don't look right....

[Scando]

I want to fit disc breaks in the rear of a 72' 240. Couldn't find alot of options in OZ ebay, so went on the US site and nearly creamed my pants on the amount of stuff they have over there for the Z (roughly 1200 items most are parts).

 

Anyway i m looking at some rotors, the guy assumed i wanted slooted only because im in Australia

"since you're in australia i am assuming you wanted slotted only?" I didnt understand this, could some one help me out.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=180218660310&ssPageName=ADME:X:RTQ:MOTORS:1123

theres the link. If anyone is interested shipping to Oz is 269USD

Is it a worthy investment?

Also which is better? (the whole point of this thread)

 

I have seen both cross drilled and slotted rotors crack on race cars due to the weak spots that both options cause.  Best to stick with ventilated rotors with no modification to the braking surfaces in my opinion.

[Zeddophile]

Just to join the rest - neither.  Stick to normal vented.  Concensus among the Alfa club sprinters and indeed most racers I've spoken to (including one or two who run in Targa Tassie!), is that cross drilled stress fracture around the holes very quickly under track conditions, and slotted doesn't do much other than chew up brake pads faster. 

 

Hence my Alfas brake upgrades was limited to slightly bigger (Brembo) front calipers and standard vented discs off a V6, along with QFM K750 brake pads all round.  Which, despite having 'Track Day' stickers all over the boxes, are awesome on the road even from dead cold, and even better when you start to push through some twistys.  And by reputation, they are also an excellent budget pad for the track, but I'll report on that at the end of March

 

Being that your rear discs will be outboard, I can't see you needing any additional cooling anyway - the rear discs and pads on a transaxle Alfa are not only tiny, but they are mounted inboard (Ie. up against the diff!), and I haven't managed to overheat them under road conditions.

 

Pad choice and fresh brake fluid is the important thing, run standard pads and you will cook them and fade them if you drive hard anyway, and old brake fluid greatly reduces stopping power.  QFM also make X500 pads (500 degree) which aren't outright race pads, but are high performance.  I had them in the front, and while they stopped well, the K750 (750 degrees) blew them away across the board in terms of initial bite even with light application, and on outright stopping power.  They even seem better cold, which leads me to suspect that maybe I didn't bed the X500s in very well - although the K750s killed them from the very first (very light) application when I'd just put them in.

 

As far as brake fluid goes, going on dry and wet boiling point figures, Castrol Super Response Dot 4 (in the silver bottle) is probably the best for most people.  It falls a little below the race fluids for dry (fresh) performance, but is a bit further behind on wet (some period of months old) performance, however it costs about $10 for 500ml as opposed to $100 a litre like some of the race fluids, and its available at almost any auto shop and a lot of servos - which means since you'd want to change it at least every year if you are driving hard, its damn good value for money.

 

If even with some high performance compound pads in, you are getting fade, then you'd go to setting up some ducting to direct air before you went to drilled or slotted discs, as its a much cheaper option, and much more effective - cooling doesn't happen without airflow.