So the Subaru conversion is up and running and I am planning for next season's track events. A concern of mine is the stock solid rotors ability to dissipate heat. I went digging in the archives but the information is scattered to say the least. Most was why Boxster calipers are not an upgrade. No kidding.

Now I am very familiar with the "upgrades" and real upgrades related to early 911s. I only want more heat capacity over a run session. I tracked my warmed over early 911 for years with stock M front calipers and had no issues. Proper brake technique, cooling ducts and decent pads can really provide excellent braking.

I am not as familiar with the 914 system upgrades. The system has been brought up to stock quality with rebuilt calipers and for the street functions just fine. I have no issues with the braking force just the ability to stay cool.

What are the options? Will cooling ducts (AJ or other) work on these cars in the same way they do on a vented 911 rotor?

What pads work well?

Can I stay with 4 bolt wheels? I do not really want the added expense of a 5 bolt conversion right now.

Are there any "hats" that will fit over a stock 914 brake "hub"?

http://www.914world.com/bbs2/index.php?showtopic=170890

If you want to retain solid rotors, the only upgrade I can think of would be great pads and a cooling system. The AJR system incorporates a backing plate that would probably put the cooling air into the hub section of the integrated 914 hub/rotor. With a solid rotor, it would probably be best to have that directed to the rotor itself.

There was a hub manufactured a while back and sold through the now defunct BRAG. It allowed a 911 vented rotor to work on a 914 spindle. You would then use a 911 M-Caliper or a Brembo caliper made for the 3" spacing. That hub retained the 4-lug setup. You might be able to haunt the classifieds for that. This is about the only option if you want to retain the 4-lugs.

I really don't think there are any other caliper options for solid rotors (BMW etc.) because a ) it sounds like you know how to drive and b ) those simply add more heat to a rotor that can't dissipate it all that fast. That's why I mentioned cooling up front.

I know 4 bolt racing cars that are dumping air onto stock non vented rotors....


Pads are still the single most significant thing you can do to brakes..
even if you have to have one set of pads for racing and another for the street.

I recommend Porterfield R-4 or Raybestos ST-43 pads.

I am running R-4's in 1988 VW Fox calipers up front.
( Fox had a solid rotor )
I will be running street pads in the same calipers on the rear as soon as I can, to adjust the bias.

The calipers are less than $25 each on Rock Auto. ( no core )
Single piston. The cylinder bores are in the air stream, not shielded by the wheel shells.
Pads are 50% larger than stock.

I use cooling ducts, so overheating is not a problem on track.
For street these should be just amazing.










The bolt spacing is 3". The mods needed to bolt them on are:
1. enlarging the bolt hole to the same size as the 914 caliper.
2. Clearencing a small amount of metal to allow the rotor to pass through the caliper. About an 1/8". The casting is very thick and there are no hydraulic passages to hit.

Now that I have fitted and tested them, I am starting fresh with new calipers, rotors and wheel bearings.


KT

not necessarily amazing on the street
the way brake pads work.... is that they are optimal in a specific temp range...

street pads never reach the temperatures of a race pad
so race pads never work well on the street....
portefields are fine. but every pad is designed for a different weight of car that creates a differnt temp range due to its weight.....

try cool carbons.
they are much more 914 friendly due to their temp ranges with a light weight car..... portefields are designed with cars over 3000pounds and up....

@ trekkor. those look awesome dude. what MC are you using?

FWIW I also used the Porterfield R4's for a few years on a stock system with good results. (I might have had the 19mm master cylinder, can't remember.) That was on a narrowbody car with 205 Kumhos.

I don't think the AJR / Smart-Racing type of duct setups will work for solid rotors. I would see how the system does with good race pads and fluid first, then try gettings some more air flow onto the rotors if needed.

I am using the stock m/c. ( 17mm )
It's old and the pedal is a bit soft for my liking.

I'm going to install a 24mm MBZ m/c this winter.


KT

Over the years, here are the things I tried. First was stock calipers and rotors (F & R) with racing pads, not great for heat removal. Next were BMW calipers on front with stock rotors and racing pads, ducts and 19mm mc, tee and this worked well until a street race in Tecate MX with short straights and the brakes faded badly!

Final setup was Brad's alloy hubs with vented rotors, M calipers in front, BMW calipers in the rear, tee, 23mm MC and never any brake issues again. The 4 bolt hubs allowed me to use Center Line 7 inch wide solid rotor wheels and Goodyear cantilever slicks which are the lightest wheel/tire combo you can probably use but are very rare! The 914-6 could out brake any of the vintage 911s by waiting an additional 50 feet or more! No brake fading ever again.

Are Brads alloy hubs available?

Even if he says they are, they aren't. I like Brad, but he's a bit sketchy on his commitments. I have a set of alloy front hubs that MAY be available in the spring. I've got a strange idea for a brake upgrade, if I muster the sack to put it together, the hubs will show up on the parts for sale section of this forum.

I am not suggesting stepping on somebody's intellectual property, but I bet there are folks on this board with the engineering and metalworking skills (and tools) to produce something functionally equivalent to Brad's hubs.

There would of course have to be enough demand to make it worth their time. I'm sure that's why Brad and a lot of other people have bailed-out on the 'boutique' 914 and even early-911 parts market. The demand is small and the flake-factor high in the old car world.

There's a set of those hubs in my shop as well as a large mill and a decent sized lathe. There's a foundry capable of casting aluminum in large quantaties as well. It could be done VERY quickly. After working with all of the above, my opinion is it's not an optimal solution. Gimme 6 months, I should be able to come up with something.

Spoiler:

I am using the 4 lug to 5 lug hub on my car. B didn't make them. Someone else did it for him. They are probably on this board now as the other has maybe 50 hits a day on a good day... Drew Montoya has Cad capable machine shop and a link to it in his signature...

@rohar - what rotor will you use with the undrilled wilwood hat?

Thanks for all the great ideas. It looks like I am going to have to fab something.

I thought about using the old rotor as a hat to mount an aftermarket rotor.

This may be useful:

914 pad on top, VW Fox on bottom.




KT

I thought the VW fox used single piston "floating" calipers...
this seems like a step backwards in technology

Truth be told, it's on the "to do list" so it's gonna be a bit before I get there. I'll be running M's up front and probably BMWs in the rear next spring. Shortest path to running and all.

That said, the Audi engine I'm dropping in the car has the possibility of generating well over 350hp. It won't at first, but you know how tuning goes. Eventually I'm gonna have to step up to big boy brakes.

There's virtually nothing available for vented rears on 4 lug so 7" hats are the only easy way out. Since they make blanks, I can just toss them on the mill with a rotary table and drill them to fit. Once you go there, there's a LOT of disks available. It also moves the disk out, toward the rim a bit so there's automatically room for caliper adapters. Maybe 'Vette calipers?

This style of caliper is on nearly every modern car and truck today.


KT

on grocery getters yea
its cheaper to produce and works..
but it is not on performance cars and not a techonological performance upgrade.
its a bigger pad, but not a superior brake design.
many modern performance cars use multiple pistons... 6 or 8 even.

You can make up your own cooling for 4 lug rotors and then run the Raybestos ST-43 compound. There is nothing nearly as good as the Raybestos pads.

Also, Chris Foley used to make ducts that went over the front calipers and forced air into the pads. Might be worth asking if he could do them again.

Yeah, can you fit them under 15" rims with stockish disks? 4 lug?

All the design constraints considered, it seems to be a pretty elagant solution.

I did this mod so I could fit them inside my... 13" rims!!


KT

There's something terribly wrong and awesome about you Trekkor.

I'm questionable...


KT

Trekkor, do you have a brake brace in your car? You should take mine out for a spin tomorrow. Stock brakes, 19mm MC, brake brace and hard as a rock.

I don't have a brace. I'd like to check that out.

I saw the video. looks promising.


KT

Just read this thread on a Subaru forum talking about Floating vs. Solid caliper design. They get a little off topic (duh, it's a forum) but what I took away from it is:

- Potentially the floating caliper design has less ability to modulate near the threshold.
- Potentially the floating caliper has more slop upon initial engagement due to the number of connection linkages to get force from the piston applied to the outer pad. All those little gaps and movements need to be closed before the pads even start to grip.

Of course, neither of these points have much to do with the ability for the caliper to simply stop the car. That is undebateable. And the way I look at it the solid caliper should have better 'feel' all around, but if you can drive fast with a floating caliper then you've got nothing to gain by going solid.