A young friend of mine bought a Wilwood big brake kit for his NA Miata. It's NOT the FM kit. The 6UL wheels grind on the calipers. He's wondering if the FM smaller kit brackets would work with his current Wilwood calipers and a smaller rotor. Does the smaller FM kit use the same caliper as the big kit and are the mounting brackets available separately from FM , or from Wilwood?
If the interference is not real significant, I've grinded calipers slightly with no problems.
What kit did he get? 11.75" or 11" rotors?
There are a bunch of kits that use Wilwood calipers, but only one kit from Wilwood. People don't usually distinguish.
In reply to Keith Tanner :
I'll ask.
Also, what size 6ULs?
If it's a Trackspeed gen1 11.75" kit, you need 5mm spacers for the caliper to clear the inside of a 15x9 6UL. The kits came with them, but if it's secondhand then they may have gone missing.
This kit with two piece slotted rotor option.
That's the standard Wilwood-sourced kit.
Different calipers than the FM Little Big Brake Kit (Powerlite vs Dynalite) and completely incompatible brackets. I'm assuming the calipers are hitting the back of the spokes, and the solution is spacers.
Tell him to install an adjustable proportioning valve if he wants shorter stopping distances with that kit.
In reply to codrus :
It's a new kit, and he's purchased some spacers separately since he found the problem. Unfortunately, he's already scored the back of the wheels and left a gouge on the edge of the nicely coloured calipers.
What size and generation wheel?
In reply to Keith Tanner :
Why the proportioning valve? Is he going to lock the fronts?
Sorry, the wheels are RPF1s , 15x7, 38mm size. He already has a proportioning valve installed, too.
BIG difference. 6ULs will clear almost every brake setup, RPF1s will clear almost none.
And yes, the reason for the proportioning valve is that the NA comes from the factory with a fair bit of front bias and increasing the front brake torque will only make it worse.
OK, I've passed all this on to him. Thank you for imparting your knowledge in such a speedy fashion. Now I'll be utilizing a proportioning valve on my Challenge build, just in case my hybrid brake system needs some tweeking. 
I've got to add this: Keith's presence and support on the grm website is one of the reasons I chose a Miata for my autocross car.
Keith Tanner said:
And yes, the reason for the proportioning valve is that the NA comes from the factory with a fair bit of front bias and increasing the front brake torque will only make it worse.
Are you suggesting to prop the fronts? Or to use the adjustable prop to raise the point at which the prop starts to limit the rears?
Oh, replace the factory valve with the adjustable so you can send more pressure to the back. You don't handicap the end that works 
Keith Tanner said:Oh, replace the factory valve with the adjustable so you can send more pressure to the back. You don't handicap the end that works
OK, I was just making sure you hadn't taken the brown acid. :-)
In reply to Lof8 :
You tell me ;_;
https://i.imgur.com/0y5rJKj.jpg
Aforementioned young (dumb) friend here. :(
Thanks to everyone for their help.
In reply to Keith Tanner :
As a follow up, I wish I had known then what I know now -- If FM had mentioned that their offering worked with RPF1's with minimal spacing and not this grinding hell, I would have bought it.
Actually, lets be honest, I just wish I had bought the FM offering.
Sorry we didn't get you the information you needed to get the right kit. We provide templates so you can check your own wheel - it's more work, but trying to stay on top of the hundreds of wheel options with every brake variable is pretty much impossible. We don't have any RPF1s to check clearance on ourselves.
Just so everyone is clear on this, Cory did not buy an FM kit. He bought a Wilwood kit elsewhere and wishes now that he had gone to FM instead.
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