Four vs. six piston

[Splangj]

Good day everyone I’m currently running a Willwood front disc conversion kit from drums on my 69 RR. I installed them many years ago, and they work pretty well. I’m almost sure they are only 10” rotors, but I’m going to check them today, along with the id of my 15” centerline wheel. Summit sells a few different Willwood kits with a 12.19” rotor, with either a four or six piston caliper. I already have a Willwood manual master cylinder with I believe a 7/8” bore. Has anyone experienced either of these Dynapro kits? And how much difference in stopping power between the four to the six? Thanks for any input or advice.

 

[topside]

Rotor size vs wheel ID is generally on the ratio of 13" rotors requiring 17" wheels with most calipers.
The calipers are the interference point, of course, but lower-profile calipers are available.
If you're already locking & sliding the tires, that's the next upgrade, assuming no other issues, right ?
All else being equal, 6 pistons should exert more power at the rotors, "apples to apples".

 

[Splangj]

Thanks topside!
I just measured my rotors, they’re 10.75. The I’d of the centerline wheel measures just about 14.125 where the caliper outside would sit, approximately an inch in from the hub face. I tried to get a photo with the wheel on but didn’t work. I could get my middle finger between the caliper and wheel with a hair of extra room.

 

[topside]

Calipers only need to clear by enough to not trap too much heat (and obviously not touch).
I think Mopar Action recently had an article on how much rotor & caliper can be stuffed inside a 15" wheel, and they went pretty tight.

 

[Splangj]

I’m going to call Wilwood tomorrow and see if they’ll fit. I want the extra rotor size if it’ll fit. I’m not willing to go to bigger wheels, I think they look weird on old cars. What are these lower profile calipers you speak of? And thanks for your help!

 

[topside]

Can't remember exactly, but think they were either Wilwood or Baer.
You might gain a little clearance by beveling the ends of your calipers, but check out that MA article; if you don't get the magazine, they're pretty good at posting their articles online, and Rick Ehrenberg - who does their tech stuff - can be found on Ebay if not FB or other online sites.

 

[1STMP]

Just my opinion of course, but if your
current setup stops your car
adequately, save some loot and don't
fall for the hype.
In a given location, you cannot put 6 round pistons with the same surface area as 4 pistons. The 6 pistons will always be smaller in overall surface area.
They do not apply a greater clamping
force, and may actually be a detriment
in a daily driver as 6 piston calipers
flex a great deal more than 4
resulting in faster pad wear.
NASCAR runs a 4 piston caliper and
we all know how many times those
boys hit the brakes, hard, to the point
of glowing red rotors. With all their
their technology and top notch
engineering, if running 6 piston
calipers would give them an edge,
they'd be using them.
Wilwood, though ther products are
top notch, would like nothing
better than to sell you their braking
systems. Even if they are
unessary for your particular
application.

 

[Splangj]

Good Reasoning on the six vs. four pistons. I’ve never really done a full skid attempt brake test, only stoping quickly as I could a couple of times. In my past posts somewhere, I stated that my Dart with 12” manual rotors definitely felt stronger stopping rapidly. Going an inch plus up in rotor size should help noticeably I would think. Like most of us, I live in deer country, and drivers have become more distracted as well as just being crappy drivers in general. Dr Diff sells an 11.75 kit with Wilwood four piston calipers, but I might need to change spindles.