aftermarket drilled/slotted rotors

herr_sparky · Post by **herr_sparky** » Mon Jul 06, 2009 1:58 pm

anyone ever bought/used these? i was going to have my original rotors drilled & bead blasted but maybe these are just as good? seems like a bargain ($246 w/pads)...

ebay item number: 140329658394

trinet rotors on ebay generic picture:

raygreenwood · Post by **raygreenwood** » Mon Jul 06, 2009 3:07 pm

Without mods.....I'm not aware of any vented rotors (radial center vents like those) that will "bolt-on" to a 411/412.
I think Wally has vented rotors, but a totally differnt caliper.

I have cross drilled rotors on my 412....and they make a big difference in spitoted driving and stopping. The slots are mainly to help shed water and to allow gas and dust package...and are hardly worth what they do to rotor strength and wearability to a rotor for anything but track service. Thats just my opinion from watching others who use them (regarding the grooves).....but cross drilling on standard high quality slotted 412 rotors with a very good set of pads, good fluid and a set of teflon stainless lines goes a lone way with just the stock system. Ray

herr_sparky · Post by **herr_sparky** » Mon Jul 06, 2009 4:03 pm

i guess i was wondering about the quality of these particular rotors... considering the Porsche crossover, what about aftermarket rotors for the 914? recommendations? a local machine shop said they could probably drill/chamfer my rotors in the proper spiral pattern (which is all i really want) for about $250 and i'd be keeping my good German-made parts...ideas? Zimmerman?

raygreenwood · Post by **raygreenwood** » Tue Jul 07, 2009 5:37 am

Unless your rotors are internally vented like those in the picture, there is no spiral pattern required.
Standard type 4 rotors are solid. The spiral pattern is required only when you have internal vents like those in the picture so you don't drill through the cast in dividers.

For our rotors....simply three rings of holes equally spaced from edge to center...staggered. Holes should be about 3/16". Anything smaller does not allow all that much air to pass through and anything much larger takes too much strength from the rotor.

I carefully drew a pattern on paper based upon spacing I had seen elsewhere. Used spray adhesive to apply the pattern to the rotor and center it up. Then I used an automatic centerpunch to mark the eaxct center of all holes
I drilled mine. I took a spare steering knuckle and mounted the rotor on the spindle....mounted that in the drill vise and leveled it carefully.

I used a two flute, solid carbide drill I bought from MSC for about $12. It cut like butter and left a machined quality hole. I drilled each ring, then replaced the bit with a six flute chamfering tool (about$15). Proper drill speed and plenty of coolant. It took about 1.5 hours per rotor.
Works perfectly, looks great and had no balance issues.

Cross drilling is worthwhile on these rotors if you drive spiritedly and especially if you live in hot climates. Ray