The vented rotor hubs will allow you to bolt on a M-Caliper but the pad size is the same as the 914 and, I'm concerned about rotor clearance with the 914 mounting ears. There's a few here using them but, it's very close from what I hear. I'd like 2mm clearance to accomodate thermal expansion of the rotor.
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with a 180hp six even 320 BMW calipers are too weak for street driving...go the billet hub route and install larger Porsche calipers to get the braking in front you need
Odd... because the BMW calipers have the same size pistons and a much larger pad than the Porsche calipers you recommend (only M-Calipers will fit on the stock strut with the 3" spacing). So, you'd actually be installing a smaller Porsche caliper.
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I would upgrade the front's & leave the rears stock. The BMW calipers are really a nice upgrade.
Well... I almost give-up on this one.
As mentioned above, the BMW calipers have the much larger pad but still reside on a 914 solid rotor (el Warpo de Rotoro and change rotors and bearings etc. all at once). You'd be matching a pad and piston size similar to a 911 A-Caliper or S-Caliper with the small #30 pad and 33mm pistons of the rear. For me this kinda gets filed under "How to mess up your 914 brake bias 101". You can do it and report back like the other guy herein about your fronts locking up and nothing in the rear.
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my brakes are still lackluster
What pads did you use? How many miles on the system since the new calipers? Why would you need new hardlines (if they're not leaking they will have no affect on your pedal performance)? Did you mean softlines? What was your bedding procedure? Did you set the venting clearance properly in the rear? And finally... what are you comparing it to?
Great pads are a must for great performance from a 914. Countless teeners get lured into "dust free, noise free" pads but, they fail to read the fine print "stop free". Need I say countless teeners get lured into CHEAP pads? There are $25 pads and there are $100 pads. Then there are Porterfields that stop like $100 pads for $59.00. If you're using great pads did you bed them properly?
New seals in new calipers need to be broken in before your pedal returns to a hard position. Bedding the pads will help with this process. This issue is outlined in the 914 factory manual under brakes. The new seals will generally pull the pistons back further than the ideal gap. This will allow additional pedal travel until the seals break in.
New rubber lines can help if needed.
Once you lock up your tires your brakes have done thier job. 914 calipers can still lock up any tread you can stick under a narrow 914. There are VERY fast race cars running stock 914 brakes and doing very well with them.
Are they big power brakes? No... they're awesome disc brakes from the early 70's. If I got out of the Cayenne and jumped in the 914 I might think things are lackluster but, if I jumped out of the 71 911 into the 74 914... things are more apples to apples. That's why I asked the comparison question. It happens often when "Mommy" who is use to carting the kids around in the Land Rover gets in "Daddy's" 914 and swears she'll never drive it again. Daddy goes out looking for a brake solution... "my wife hates my 914." Common.
Hope that helps.