911 Brakes 3" vs 3.5", What am I missing and Options

[jesiv]

Ok so I am upgrading to a 911 suspension (Seperate Thread http://www.914world.com/bbs2/index.php?showtopic=87337 ). Then I hear brake caliper bolt spacing 3.5 vs 3.0. So (IMG:style_emoticons/default/WTF.gif) WTF is 3" vs 3.5" Am I making a mistake going with 3.0 vs 3.5? I really don’t understand the issues. Do I care?

Thanks for real world opinions!

Regards,

James

[PRS914-6]

When I make a change like this I always try to get the best bang for the buck. In this instance why spend money on 911 3" when you can probably get 3.5 spacing for about the same or a little more. In the future you will have more options for those struts including kits with adapters for very large brakes if you ever need them.

I battled this same decision and decided to go right to the max. I'll never need more. 964RS brakes on 3.5 spacing with adapters. The cost was only a few hundred more than going with smaller components You can also see the red Tarret sway bar done at the same time with additional reinforcing added

[ArtechnikA]

You can also see the red Tarret sway bar done at the same time with additional reinforcing added

I'm not sure I agree on the really big brakes but if 'A' calipers can be had for the same price out the door (insluding the strut package) as M's I couldn't argue. Of course, he already has the '72 M-brake struts sogoing bigger could be considered an upgrade path. Swapping in a pair of built-up big-brake struts 'should' be an afternoon job.

(And I'm sure I wouldn't have painted the brake pipes, but it's your car, do what you like...)

AFAIK, Ira Tarret is the only one who 'gets it' that the 'standard' 8mm droplink hardware is marginal - his stuff is 10mm. (Lost a car to droplink failure, this is a sore subject with me.) The 911 project will be using Smart bars but Tarett droplinks.

FWIW, and out of the scope of this thread, I'm reconsidering my long-held belief on disk slot direction. I've always done it the way you have it, which matches the drilled-rotor pattern on 911's.

However, Brembo is recommending the other direction on cars with trailing calipers. After years of doing it the traditional Porsche way, when I did the slotted rotors on the Subie (trailing calipers) I went with Brembo's suggestion. *Mostly* I think it doesn't matter. The only place it seems to make a visible difference is the angle at which the slot first contacts the edge of the pad. This may be a distinction without a difference - like I said - I'm thinking about it.

I still mount drilled rotors with the spiral in the conventional direction, even tho my drilled-rotor cars have straight vents, not the curvy ones that inspired the pattern originally...

[PRS914-6]

FWIW, and out of the scope of this thread, I'm reconsidering my long-held belief on disk slot direction. I've always done it the way you have it, which matches the drilled-rotor pattern on 911's.

Actually the slotted pattern is opposite the drilled pattern with the slots running "forward". I slotted them myself. The reason being to not have the slot run between the reinforcing and vanes in the rotor creating a weak spot. I do however agree it does not matter from a functional standpoint, only a strength standpoint.

I made sure to stagger the slots on each side to make sure grooves were not close to each other.

As for weight, the calipers are very light. The big negative with big brakes is the large rotors, not the calipers. They are considerably heavier and have more rotating mass and unsprung weight. It's also the positive since they can absorb so much more heat. Building car a is a trade off and you have to decide whats important to your application...ability to shed and absorb heat or light weight.

Here is the difference between my rotors and stock 911. A huge difference in mass and heat absorption ability. Do I need all that? eh, probably not but it cost the same as the smaller ones and they have unbelievable stopping power.