ap racing cp6665 on e92 m3

[frostie77]

folks and break experts,

i have a possibility to get a set of used ap racing cp6665 for very little money.

now i am trying to figure out if they will fit on the e92 and what is needed for a complete setup.

as far as i know the mounting hole centers are equal to the cp5095 which is used on the gt4. that means i can use the caliper bracket that is available through bmw motor sport to mount them to the car, however, the offset is 35mm instead of 42mm, meaning i would need a different rotor/bell hat which honors the 7mm difference. I am planing to use ap 378mm disks as they are mounted on the gt4.

has anyone the dimensions of the front disk hats of the gt4?

and the even more important question... am i forgetting something?

Cheers

[JAJ]

Do the piston sizes work?

[frostie77]

Good point! Already checked on it and it seems that the piston sizes are identical to the gt4 caliper.

[JAJ]

If I were doing this, I'd be thinking in terms of custom-made brackets rather than custom hats. If you move the rotor inboard, there's a risk that it will reduce clearance between the back of the rotor and the suspension ball joints. It's better to move the caliper outward. That way it sits where the GT4 caliper sits, not 7mm further inboard.

That said, make sure there's enough room in the back of your rims for the caliper. It takes 25mm deep pads, so it'll be about an 3/4" wider from outside to inside than a normal street caliper.

[frostie77]

I was hoping to do the job without needing custom-made parts, but I see your point, it would be rather simple to have someone make a custom bracket for the caliper.

I did some research in regards to other available big break kits and saw that pfc makes a package including the zr31 caliper which has the same specs for the mounting hole centers (210mm 35mm). i guess this would point to enough clearance... at least one would hope...

Yes, the ap racing calipers are wide... almost 200mm but it should fit in a 10 inch rim with no problem... I will check on that...

[jritt@essex]

Originally Posted by frostie77

I was hoping to do the job without needing custom-made parts, but I see your point, it would be rather simple to have someone make a custom bracket for the caliper.

I've heard the above statement from more people than I can count over the past decade, and usually it doesn't end all that well for them if they go the custom brake route. While the idea of creating a custom caliper bracket and disc hat (both of which you would need to implement the CP6665 on an M3) sounds very simple, it is a lot more complex than it appears at first glance.

When looking at designing these parts, here are some things that you'd need to investigate:
• First, you'd have to take extremely accurate measurements on the vehicle. We use a CMM (Coordinate Measuring Machine) that is accurate within .001". Proper measurements are critical to getting the parts on the car in proper orientation. It's just like anything else…garbage in= garbage out. If you miss a measurement, you need to scrap your parts and start over.
• Along the same lines, designing with CAD allows the designer to see the parts before time and money is spent on a prototype. Do you have the capability and software to design the parts, or will you pay someone to do so? Would you use rapid prototypes to mock something up (SLA), or would you use actual aluminum parts?
• Do you (or whoever you had build the parts) have the knowledge to understand the stresses that a caliper bracket and hat experience under a multi-G load on the racetrack during a braking event? For example, how much material should you use on the bracket, and where do you position it to provide the optimum strength?
• What aluminum alloy do you plan to use? Will it hold up when in contact with a brake disc running at 1200 degrees F?
• What type of fasteners will you use? Will they hold up to the above as well? Where will you source them?
• Will the hats be designed to allow for max airflow into the disc vanes and across the disc faces?
• Have you calculated the brake bias impact for the disc diameter and the piston sizes in the CP6665 caliper? How will the change impact front to rear bias or your ABS system?
• Where will you have the parts anodized for corrosion resistance, and how much will that cost?
• Does the caliper inlet port require a custom brake line? Where will you have those made, and how much will it cost?

Making custom parts is certainly doable, but it's not nearly as easy as most people think. The above list is just a few items off the top of my head. There is a very long list of issues that needs to be addressed to ensure safe, repeatable brake performance.

Brakes are a safety item, and not to be taken lightly. When you're hurtling at a track wall at 140 mph, you don't want to be questioning the knowledge, experience, and ability of your brake designer. Just about every customer I've dealt with who went down the custom route ultimately ends up coming back to us for one of our off-the-shelf solutions. That's after they've already wasted a ton of time and money.

Below are a couple of pics that I got from a customer last week. A while back he was in the exact same position that you're in now. He had someone design custom brackets and hats so he could install some AP Racing calipers. He now has some worthless and extremely dangerous parts to dispose of, his car is out of commission, and he's spent a lot of money and time. Fortunately he caught these parts before they got him hurt!




My advice: Buy our Essex Designed AP Racing Competition BBK and call it a day. You place the order, we ship it out the same day, and you spend a few hours installing. All of the above items and many more have already been worked through. All you have to do is enjoy it, and beat the heck out of it. If you run into trouble, you call us and we help. It's very simple, will save you time and money, will perform better, and be safer than going the custom route. It won't be quite as blingy as the CP6665 on a huge disc, but it will get the job done on the track better than anything else out there. Our kits are proven, and you can read a bunch of reviews from happy customers on our blog.

Hopefully that all makes sense, and let me know if you have any other questions.

[frostie77]

Thank you very much for your input! I totally agree with you that i would not be able to fabricate my own caliper brackets or hats and i truly do not want to end up like the poor fellow you are talking about. On the contrary, I am sure I could find someone with experience in this particular area who can provide me with either brackets or hats. I am just not sure if I want to go this route.