355 challenge calipers???

I know my ABS works, and in all cases the pads/disks were in good condition, but in all of the cases, I stood on the brakes and it just felt like I could use more stopping power, because the car just did not slow down fast enough.

I may try to Stoptech brakes

 

It sounds more and more like a simple change in brake pads may solve your problem though. Brake pad manufacturers should be able to provide a cold and hot coefficient of friction for you. This is referred to as Mu. Values for Mu go from 0-1.0

Caliper clamping force X Mu = friction force applied to the rotor.

So, let's say your caliper is capable of outputting 4500 pounds of clamping force during a full 1.0g stop. If the brake pad Mu is 0.35 (pretty normal for a street performance pad) the friction force applied to the rotor is reduced down to 1575 pounds.

Next, the torque force generated by the pad acting on the rotor is calculated as: Friction force x effective radius of the rotor. The effective radius is the distance from the hub center to the centerline of the brake pad. A 5.6" effective radius would be about right for a front big brake system that uses a 14" rotor. That would generate 8823.33 inch-pounds or 735 foot-pounds of torque at the rotor.

Working the math, you can see that if caliper clamping force and rotor effective radius are held constant because they are predefined by the brake system specs, then changing/increasing the Mu on the brake pads is the easy variable that you can control.

Generally the advantages of a big brake kit on a car like a 355 which already has a good factory system will be most noticeable on the track. Meanwhile, a change in brake pads will be most noticeable on the street.

Hope that helps!

 

Thanks Greg,
That does help a little. I did change my pads and it did help, but seat-o-the-pants, I have felt firmer, stronger braking on other cars (Porsches mostly, and cars with CC brakes, but they don't count).

I wanted to get the same feeling out of my car's brakes and figured that an upgrade to bigger brakes would be the ticket.

Thanks for the input

 

As an exapmle: I have 5K track miles on my unmolested brake system (stock everything).

If I keep fresh fluid in the system (full flush before track day) the only factory weak spot for street tires is the factory pads. At high speeds they go from cold to too-hot almost instantly. A better pad (such as Ferrodo DS2500) makes this problem go away. I have run 72 minutes in 103dF texas heat, circulating within 2 seconds of lap record, with the completely stock system with the simple alteration of pads.

If you go up to R-compound you may be able to generate enough heat that a little more pad (DS3000) might be useful. Only if you go full racing slicks are bigger calipers actually warrented.

But before going to bigger calipers, you should consider using NACA ducts in the diffusers to duct cold air to the rear brakes (ala challenge cars), and add a second air feed at the front to double the air towards the caliper and rotor.

Just adding calipers and rotors does not reduce stopping distances. These are limited by tire traction, not by the ability to generate heat (calipers and pads). You can go from the factory pads (mu ~= 0.42) to semi race pads (mu ~= 0.53) and get a substantially harder feel at the pedal with less effort and less cost (to say nothing of upsetting the brake balance F/R).

 

Not necessarily! A lot of that is how much power boost the car has. I can tell the Ferrari system is lightly boosted, but has good feel. My wife's Mini has MUCH more sensitive brakes (which sounds like what you are after) but they're in fact a lot smaller in size than the Ferrari brakes and the weight difference between cars isn't that much. They just have a lot of boost (too much for my taste).

 

Thanks Mitch. I will change them out and add more cooling and keep you posted.

Bobzdar, Thanks for the input - no, don't want over-boosted brakes

 

Mitch, how are those pads on the street? I switched to Hawk black pads from PFCM's on my other track car and didn't lose anything detectable on the street but had much better results on track. I didn't really care about the street performance on that car, though, it was just a side benefit. I was thinking of swapping to something similar on the 355 this winter as I plan to track it but would want to retain decent street manners. I'm not at all concerned about brake dust as that's easy to clean and plan to run Pilot super sports or Direzza Z1 start specs. It currently has brand new pads and rotors, so it really wouldn't be much of an issue to swap for the track and then swap back for the rest of the time, but if they're good on the street as well that'd be a bonus.