4 pot versus 6 pot calipers

[scott coyle]

I would say the 4 piston set up is probably enough. I run the 4 piston front and rear, castrol srf, balance bar and 3/4 front master, 13/16 rear master. I have cooked a bunch of fluids and pads to determine this set up. I run PF 01's in front and an r4 porterfield in back. This sytem wil stand up to road america and a high altitude airport track. Huge brake zones at both tracks with 650hp pushing the cobra. I run front ducts.

The PF 01's are the best pad I have found. They only work well when braking really hard and the harder you break the better they work. I also run a bunch of rear brake bias. I keep adding rear brake until the rears lock in a straight line, then back it off a little and don't trail brake.

Good luck,

Scott

[Ant]

Scott,

Your setup and experience makes good sense to me, I have just been on the phone to Wilwood in CA, and they recommend the 120-6385-RS for my setup, Narrow SL6R with Thermotech pistons, these run a 16mm pad.

They are their narrow caliper but should be real good, so now the next stage is to make my hubs up, mount the rotors, and do a real world measurement, because I might just be able to squeeze the wider caliper in which runs the 20mm thick pads, and it may be borderline but I could run their nice 4 pot 1.88/1.75" differential piston caliper, but they are lug mount, and I think radial mount would be easier to fabricate for this setup, hence the SL6R.

Aussie Mike,

The AP's, Alcon, and Brembo prices for me are just way out of my logical thinking, and I cant justify the expense, (poor hard up old wage earner) the wilwoods are cheap, one downside is they have no dust seals on any of their performance calipers, but that would apply to the better brands also, the wilwoods are no heavier than these gold plated calipers, wilwood supply thermotech pistons at not much more expense. NZ V8 Supercar type series Holden/Falcon saloons are running the 120-5960-RS, SL6R calipers with alloy pistons, and some Dynalite 120-6985 calipers on the rear, and those guys are really doing it in 1450kg saloon cars, which surprises me a bit as the pad area in the SL4 and SL6R etc is the same and not overly large. I dont know the rotor size for them but would emagine either 13" or 14" which 1" obviously makes a big difference in leverage and heat transfer capability.

[D-CEL]

With similar piston area, and caliper mass, performance will be identical. The only true advantage of a 6 piston vs. 4 piston is control of pad taper. The leading edge pistons are smaller to reduce the clamping force so that the pads will wear evenly. On race cars with complete pad and rotor wear over the course of an event, this is important.

The key is to use the smallest / lightest caliper and rotor package, that can absorb the energy (heat) your car produces, then shed it prior to the next input cycle. The system must have sufficient mass to absorb the heat while keeping the pads from exceeding the maximum temp (fade) or causing the fluid to boil (fade).

6, 8, 10 piston calipers look great (to me) but they offer very little performance advantage over a properly sized, differential bore, 4 piston unit unless you are in a 10/10ths application.

Wilwood vs. AP vs. Brembo……
Once upon a time I was a manager @ Wilwood. During my time there, I was afforded the opportunity too play with every bodies toys. I can say without question that the high end Brembo and AP offerings are fantastic parts. Beautifully machined, and assembled. They perform as a very expensive caliper should, perfectly.
However in blind testing, there is no perceivable difference between them and the Wilwoods.
I am asked on a regular basis “Why are Wilwoods so cheap?”
My response is always: “Your question should be, why are the other guys so expensive?”
Are you getting a great caliper from AP for $900.00? Absolutely. Is it $500.00 better than a Wilwood? Not to me. Its nice to be able to buys pads for $50-$60 a set and replacement rotors for $70.00 -$100.00
Many people perceive value in the higher cost item “its more expensive, it must be better” Also a discussion we had many times @ Wilwood.


Hence the name
D-cel

Jason

P.S.
Still a Wilwood dealer if anyone needs parts

[rdorman]

What D-Cel (Jason) said. Although I seem to recall some staggered bore 4 pistons as well. Either way, Wilwood is the best bargain in performance brakes today and their full disclosure of technical data such as the temp vs cf charts on their pads make it, at least for me, my first stop if I am designing a brake system for some one. My oldie but goodie Unique uses an MG front end and the wilwoods don't fit... at least until I was done machining their hubs they didn't. It was worth the time. The difference from the Girlings is nothing short of miraculous.

Jason... did you ever get my brake work sheet? It is in Excel and you can enter all the paramaters (everything from aero CG's and specs down to tire CF) and play with the combinations on paper before you try it in real life. You would probably have fun playing with it. Email me and I will send you a copy. Also, The wilwood kit I modified to fit the MG spindles was a 70 chevy mid size kit as I recall with 10.75 rotors. I want to change those out for the 12.19 so I will be in touch!

[Ant]

Jason, Scott

Thanks for your advice, and I agree a nice 4 pot setup will do a good job, once all the right pad compounds etc is sorted!

I have decided to go to the Wilwood SL6R #120-6385-RS caliper, as it still runs 20mm common pads, and has a narrow outboard body, which after having another measure up the SL6R gives me a bit more badly needed clearance. This problem arose as the Compomotive wheels have less offset on the hub mount than the Trigo which reduced my caliper clearance, Compomotive told me that the wheels were the same..........!?!
For the rear of car I am trying to find some calipers, from a hi-perf road car which have a handbrake incorporated, plus on the rear to keep it simple I have access to rotors/hats all one piece factory eg BMW etc that I can adapt to the rear!

[D-CEL]

Ant,

Wilwood now has a hydo-mech rear caliper as you are describing. They call it the "Combination Parking Brake Caliper"

Here is a link: http://www.wilwood.com/Products/001-...-cpb/index.asp

The only problem I have found with this type of rear caliper is its lack of mass and surface area. In a Hi-perf/track application, you must run a lot of front bias in the system to keep the rears from boiling out the fluid.
This is a common problem on early Vipers. When the owner does a pad-line upgrade (which they desperately need) The rears get hot so fast that they boil the fluid, burn the seals. Then fluid squirts onto the red hot rotor and bursts into flames!!
Cars with good rear weight bias (Cobras &Vipers) benefit from a little more rear caliper. I like 1” bore Dynalites or NDL’s and then use the Combo caliper as the P-brake only.

Jason

[Ant]

Jason,

Thats the thing with these cars and they need good rear brakes, also the more calipers on the rotor the less air around it for cooling. With the handbrake I can get dispensation for a hydraulic handbrake while I own the car, which maybe a way around it!

The Dynalites with 1" bores seem to be popular with a lot of race guys here for the rears. I have also seen very good Jap hi-performance 2 pot calipers grafted into setups, and as mentioned one piece ventilated rotors 11" & 12" available in different offsets here for $60-$80, we have guys here that have built some of the fastest race cars in NZ with a very simple rear common setup, but I as you mentioned there is potential for uneven pad wear with less than 2 pot calipers.