Grassroots Motorsports magazine, Dec. issue has 914 brake tech article Options

[SP9146]

I don't usually read this magazine but saw on the cover a mention of the 914 article so I bought it. Excellent explanation of the upgrades to BMW front calipers, etc.

This was actually one of the last articles in a series about their 914 project car. Has anyone read any of the articles, are they worth trying to find?

Pete

[Brad Roberts]

Yes on number 1. Heat is the idea. But the ONLY problem with stock brakes is their ability to dissipate the heat that can be generated with the stock components. Adding a larger caliper/pad induces this heat MUCH quicker and causes fade almost twice as fast as a stock setup (semi makes sense..almost double the pad area).

Number 2. The BMW has thicker solid rotors than the 914 and the actual circumference is much larger compared to a stock 914 rotor (more swept area to help cooling). I would have to argue about the weight.. I dont think that they weighed that much more than a 914.

Ill will ?? here ...ha ha No way. All are welcome. We test everything on the race track. Some idea's work and some dont. We have pushed the factory brakes as far as anyone can push them (we have to run them in our stockish race classes.)

Bottom line: Will the BMW's stop the car? Yes. Will the 914 calipers stop the car ? Yes Will the BMW's fade first from multiple stops ? Yes Will the 914 calipers fade from multiple stops ? Yes, but you will get almost twice the amount of "attempts". It is a trade-off. I also happen to enjoy controlling my cars from a panic stop instead of "locking them" imediately like we do with the BMW calipers.


B

[F4i]

Again thanks, I have not tried the BMW setup and intend on autoX occasionally that is why feedback is welcome. I am glad ill will is hard to come by here. It can be very easy to aggravate some people unintentionally or by having a difference in opinion. (Brad)Will you be making a vented 4 bolt kit for the teener? I could not ascertain from previous posts.

[Brad Roberts]

Yes. The first ones come off the CNC lathe 2nd week of Jan. It is a new hub that accepts a stock 911 SC vented rotor. They can be drilled for 4lug or 5 lug and accept stock 914 wheel bearings. The plan is to sell them in kits complete with wheel beerings (races installed) wheel bearings seals, new drilled or slotted rotors..or solid... and rebuilt 911 calipers that will bolt directly to your struts.

We raced this setup in SCCA back in 1993-4-5-6 on a GT3 914. It should change the industry. You will no longer be forced into 5 lug wheels to achieve better braking.

Soon after the release of this new hub.. we will have a hub/rotor/caliper combo that allows you to run a HUGE 930 Turbo brake pad on a HUGE 930 style vented rotor..all under a stock 2.0 Fuch alloy (way overkill...LOL)


B

[biosurfer1]

so i can start saving my pennies now, how much are you expecting this kit to be?

[Brad Roberts]

I dont have totals in front or me.. but the plan is to be several hundred less than what it would cost you to convert to 5 lug. Plan on no less than 700$ for EVERYTHING.. hubs/rotors/bearings.. blah blah... you save: $$$ not having to buy 5lug wheels.

The number one answer we get when we ask about the reason people convert: (to get more selection of wheels).. then everybody runs stock 15x6 FUCHS..LOL

We will have a 5 lug hub also..


B

[biosurfer1]

sounds right up my alley...i found a great set of polished fuch's but have been passing on them so far because of the cost to convert correctly, might have to give the guy a call now and renegotiate...

[Brad Roberts]

This is driven buy a recent racing rules change.. we are now allowed to run anything that came "brake wise" on a 9146 (which was vented rotors and M calipers).. so this is my underlying reason for doing this.. just so happens.. daily drivers can benefit also.


B

[JoshuaSkinner]

Brad,

I don't understand how slowing a car from 60 MPH to zero in 200' with different sized brake calipers can possibly put different amounts of heat into the rotors. You have X kinetic energy in the car that will be converted into heat in the rotors, pads, etc. If the brake balance stays the same then the front and rear rotors will still have to absorb the same amount of heat energy. I know the brake balance is an issue with BMW calipers, but I think my point is clear.

I do understand that a larger caliper will inhibit airflow more than a small one, but how much rotor area in square inches or as a percentage of the total are we talking about? I think if the brake balance can be restored that the fade problem experienced with the BMW calipers would vanish almost completely.

I'm looking in the SCCA ITB specifications (yes, both a 320i and a 1.7/1.8 914 are ITB cars) and the 914 has an 11" diameter front rotor and the BMW is only 10" so there goes your swept area argument. And the rotor thickness difference is what 2 mm? So I'd bet the rotor mass of a 914 is probably greater than that of the 320. But the weight difference between a 914 and a 320 is how much? I'll bet money that the 914 has more front rotor mass per pound of car than the 320 does. SCCA race weights are 2460 for the BMW and 2080 for a 914, BTW.

In any case I think I'm probably going to try some Volvo calipers on my 914 and see what happens. I go wrecking yard shopping tomorrow.

Joshua Skinner

[campbellcj]

Joshua - what you're saying does sound logical and it's been a loooong time since college physics. (IMG:style_emoticons/default/idea.gif) But I think the variable you're not accounting for is -time-, i.e. all things being equal, a larger caliper and pad will convert more kinetic energy to heat per unit of time than a smaller one. In other words, the BMW setup will generate more torque on the rotors and thus more output brake HP than a stock setup. So the larger "unmatched" pad/caliper setup could potentially overwhelm the ultimate heat-dissipation characteristics of the stock rotor which is not designed to dissipate a sufficient amount of heat in that amount of time.

Conceptually it's similar to launching a stock 2.0 from a stoplight vs the same exercise in a 350cid V8 conversion, with the identical tires, suspension etc. The torque and frictional forces on the V8's tires per unit of time will overwhelm them.

In fact, since I touched on the subject of tires -- they are the #1 performance tuning factor in braking once the brake system in question is in optimum working condition. A car with sticky tires will immediately show braking improvements over one with inferior tires. A LOT of people seem to forget that, and dump time/money into their brakes then their tires can already barely match the friction demands of their stock brakes!

[J P Stein]

That's it, Josh, jump in with both feet.

I'm not smart enuff to figure out if Brad is correct or not, so I'll pass on this aspect, but.........

IMO, a "brake upgrade" must add:

Mechanical advantage....as in larger dia rotors.
Increased heat sink or cooling.

Bigger calipers "usually" come along with the above hardware. Calipers by themselves aren't much of an upgrade, IMO. They do add some heat sink on the caliper side of things. Josh, those Vulva calipers weigh about 250lbs ea ....great heat sinks, tho:lol:.

I would be less inclined to add better brake pads to this short list. What's good for a race car will suck on the street or at an AX, so "better" is a relative thing.

[914werke]

Yes. The first ones come off the CNC lathe 2nd week of Jan. It is a new hub that accepts a stock 911 SC vented rotor. They can be drilled for 4lug or 5 lug and accept stock 914 wheel bearings. The plan is to sell them in kits complete with wheel beerings (races installed) wheel bearings seals, new drilled or slotted rotors..or solid... and rebuilt 911 calipers that will bolt directly to your struts.

So Brad if Im following you correctly, in the next 45 days your inital setup will be the delivery of a "hub" that will allow vented 911 rotors to fit the OE 914 strut spindles, so we might retain our 4x130 wheels and benifit from 911 M (steel) calipers?

Cool, just to be dificult is it possible for that same or similar hub(or diff. bearings) to be applied to the later 3.5" 911 strut spindals(replacing the 5 lug hub), to retain the same 4x130 wheels but use say.. S calipers?

[brant]

I wanna throw in my $.02 too...

1) the grass roots master brace looks ugly and heavy... We have used much more graceful pieces for the last 8-10 years...
bolt or weld something onto the cross brace that points back and cradles the MC... then put a couple of hose clamps over the MC and this brace....
(to remove the mc, just loosen the hoseclamps..)

2) Man... STOCK brakes when rebuilt are more brake than is needed on 99% of the -4 race cars....
Add cooling air, race tires, and pads to a GOOD functioning stock caliper and you will have more brake than you need.... These are momentum cars... if your using your brakes enough to over heat them then you should not be using your brakes soo much...

Sorry I just felt like yelling
brant

[bernbomb914]

Brad will you make a vented rotor that will bolt on to the stock hubs. some of us have already rebuilt our hubs with new bearings etc. and would like to purchase the vented rotors only?

Bernie

[Brad Roberts]

Right now I have not even checked with the machine shop to see if they are done (figured they would call when ready.)

Bern, you have to use our hub. No way around it. The bearings/races are cheap. Stock rotors are cheap also.. you wont be out that much.

Joshua,

Run them.. I dont care. I'm telling you that people with 100's (yes 100's) of SCCA National wins have been doing it on stock brakes since the 70's. Learn to drive is the moto I follow. We now run vented 911 rotors with the same size brake pad. We ended up with better cooling and NO issue with fade. Put big reds on it for all I care. I personally wont sell or install the BMW stuff. I would rather figure out why your stock system isnt working properly. On some of the cars, we run 4 front calipers (makes buying brake pads easier) and then balance them with an adjustable bias control. Brakes is the one area where I have seen it all and dealt with it all. Stock system still works.

B

[J P Stein]

Brant:

I've always wondered about the term "momentum cars".It seems to get bandied about when talking about 914s.

Does that mean you carry as much speed as you can...at all times....just like a non-momentum racecar?

Or does it mean that if you screw the pooch on a corner, it takes a lot longer to get back to speed?

Or does it mean you better get the other guy in the twisties cause he's gonna hand you your hat on the straights?

I ain't being a smartass...I just don't get it (IMG:style_emoticons/default/confused24.gif)

Go ahead and yell, I can take it. (IMG:style_emoticons/default/laugh.gif)

[Brad Roberts]

I'm not Brant..but..

Momentum cars are cars that appear in your mirrors suddenly but cannot pass you on the straights. It means he is faster than you. It also means we rarely even *touch* the brakes. I watched it all day today. People with BIG brakes and BIG engines come up to the corner as fast as they can and bring the car to almost a complete stop before turning the corner... then use all that BIG power to exit the corner. Basically NO entry speed. A momentum car carries almost the same entrance speed as it does exit speed (no MPH loss.) People who learn momentum in under powered cars go on and learn to be VERY fast in cars with power. They are typically smoother in the powerful big braked car than the new guy. They know how to use the power and keep the car on edge. People who come out of go carts already know momentum.


B

[F4i]

125cc (2stroke) sportbikes. Same deal

[Brad Roberts]

We have basically beaten this PCA region into submission. "If you see a 914 in your mirrors that was NOT there prior to the last turn.. HE IS FASTER THAN YOU and probably NOT in your class.. a slight lift on the straight to let him past you"... << this is echo'd in EVERY event held in NorCal if they see 914's in the paddock (during the drivers meetings).

It gets real old riding the bumper of a 911 waiting for him to F-up in front of you...


B

[Dave_Darling]

True, but it feels so good when one finally pulls over and points you by... (IMG:style_emoticons/default/smile.gif)

--DD

[J P Stein]

Hummm.....it's even more fun to blast by them on the straights, regardless. (IMG:style_emoticons/default/laugh.gif)

My one only DE:

Novice group, of course. The were a couple cars that I couldn't pull on the straights. I found that if I backed off them prior to the last section before the straight I could get a run on em' and exit the corner 10-15 mph faster than they......then they were dog meat. (IMG:style_emoticons/default/smile.gif) .....then the back end started moving around....oops. (IMG:style_emoticons/default/blink.gif)

Call that momentum if you want. I'd call it higher corner speed. I did find that while following these folks, I never had to touch the brakes going thru the twisties. On my own, going thru there, I sure as hell did!