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

yes, its a pretty good build. Is it the green 914?

Yeah its the green project car, Sean. All of the articles are worth reading and getting back issues.
Do they give out secret info or how to build a 130hp Djet 914? No. Still lots of good ideas worth checking out and filing away for future use.

Geoff

I believe they are offering a package deal on the 914 issues.

They also have a good BBS too. Check it!

Grassroots Motorsports

Has anyone else done the "back up bolt" on the cross member trick that was shown in the article??? I never saw anyone mention this mod in any of the bbs threads. It seems crude, but simple. I didn't realize there was that much flex in the pedal cluster mounting area, maybe I'll beef mine up while I have it apart. Somehow the backup bolt is just too easy, I have to make this harder on myself

Flex if you have alot of rust...

I didnt see that much flex when I was putting my M/C in.. But hey, What do I know?

Andrew

I was impressed by that trick as well, would be interested in hearing from others if it was effective. It was enough to get me to buy the back issues! Wonder what they came up with for the suspension... 100lbs rear springs and some Konis?? Thanks for the tip.

has anyone been able to find the GRM sister mag in a bookstore?
(Classic Motorsports)

yup

Which one?

I have looked at 2 or 3 now (Barnes and Noble and Borders I think) and no sign of it.

Is it any good? I wish they had kept the two mags together, I don't really want to subscribe to two when I hardly ever finish all of one before the next one comes out.

magazine shop in Hermosa Beach. I haven't seen it in Indy though

Found it last night @ B&N. Full blown feature on the green 914.

Funny. I found an update on the brakes they installed.. they cannot get the bias correct in the car..>LOL

DONT USE THE BMW SETUP.


B

Oh.. yeah.. We have used a weld in brace for years on the race cars. Not really needed for a street car unless your tub is rusted in that area.


B

i have -something- going on in the pedal box of the 911. there is the usual open-car surface rust in the area but it appears structurally sound; i don't think that's what i'm seeing.

with my right foot applying constant pressure to the brake (stopped at a light, for example) i can feel the pedal move when i depress the clutch. it may have got a -little- better when i rebuilt the cluster with bronze bushings (the few surviving plastic bushings were toast) but it's still evident. i didn't see any pedal shaft wear, and the pedal box bolted securely back into place (after a liberal spraying to the area of LPS-3...).

i know i'll be back in there to replace the MC when i uprate the brakes (i suspect it's a 19mm instead of the NLA 20,5 it should have ...) and i'd like to fix whatever's actually wrong when i do.

I definitely used to feel that on my 911 and it didn't have any significant rust in that area. I just thought it was bad bushings.

Hi, short time lurker on this site. Long time lurker on PP and DGI. Brad, What is wrong with the BMW setup? You are the first I have heard say anything bad about it. I ask because I cannot afford 911 bits/wheels etc. but want better performance. Thanks

Thanks for posting..

Porsche spec'd the calipers/pads to match the rotor thickness. Adding a larger pad/caliper to a solid rotor is playing with fire. You have now introduced more heat into an object that has trouble dissipating heat already. What you get with the BMW setup is instant gratification in the first stopping tests. What you end up with is faster brake fade because of the heat that is generated with the larger pad/caliper.

Installing larger calipers on the front and doing nothing with the rears screws up the brake balance that Porsche was trying to achive. GRM installed a rear adjustable brake bias and annouced several times that they couldnt get the bias adjusted correctly.

Several "professionals" will tell you that the stock system is more than adequate in stopping the car multiple times. People jumped on the bandwagon with the BMW stuff because it works great when you replace everything and rebuild the entire brake system (which is exactly how the stock brakes would work if replaced/rebuilt everything).

The issue is heat. Always has been always will be. Adding a larger caliper to a solid rotor is not very smart. You have "home" engineers pushing brake products on people... is this smart ??


B

Oh.. I'm biased.. we have a vented rotor solution coming out in the next 45 days that will allow you to keep your current wheels/tires.

I was complaining about the BMW crap long before we decided to move forward with the 4 lug hub/911 rotor setup.


b

If the stock brakes are in good working order, they work great. I don't autox, but we have nothing but 2 gear streets here in the city.. I do alot of stopping.

Seems like the only real step up is 911front-914/6rear, otherwise, I would use that money on seals, or new wiring.. etc.


M

Thanks for the response. I have noticed that yourself(Brad) and another (Mueller?) are working on an alternative solution. More information on this would be of great assistance in making decisions. 4 bolt with vented rotors ARE the ideal! I have a 74 (orig. 1.8) with a balanced euro piston 2.0 that is currently under full rusto. I wish to be driving for spring. I would like to make a couple of points to consider. As for "home" engineers wasn't one of the original proponents of the swap Mr. Kaufmen?sp. an engineer? Also, I agree that more heat is created however: 1. That is kinda the point right? Greater friction= more stopping 2. The BMW is a heaver car with solid rotors. Were there heat problems with them? I am not trying to argue by any means. I certinaly do not want my first posts here to be the start of ill will as you guys are certinaly more knowledegable than I. I am as I said more interested in you're kit than any other option. And a big fan of (brackets) Happy new Year!

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

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.

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

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

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

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...

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

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

Joshua - what you're saying does sound logical and it's been a loooong time since college physics. 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!

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.

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?

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

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

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

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

Go ahead and yell, I can take it.

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

125cc (2stroke) sportbikes. Same deal

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

True, but it feels so good when one finally pulls over and points you by...

--DD

Hummm.....it's even more fun to blast by them on the straights, regardless.

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. .....then the back end started moving around....oops.

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!

Its all about making heat in a consistant way then getting rid of it.
Street driving and auot-x do not need larger than stock brakes. You just need a brake system that is easy to modulate or feel what is going on and makes heat ASAP. The the bigger BMW calipers will make more heat sooner but I have heard they are more difficult to modulate.
If they start fading it is time for more mass in the rotors and, or, more cooling.
Having said this I have the BMW brakes but i have not yet installed them on my v8 914.
My stock system with the propotioning valve replaced with an adjustable valve works great. But I bought all the BMW stuff (all four calipers) when he stock system was not working 100% because I thought the stock system was not good enough.
Since i have the BMW calipers I will install them and see what the difference is.

George

JP,

I certainly don't consider myself an expert by any means... but here is a few observations I've had over the years..

I hope this doesn't come off as condensending or angry.. I'll just try and explain my own thoughts about the momentum question.

my old car had big brakes and vented rotors front and rear... The fast guy in my class had stock brakes and could out brake me into the corners..

After years of observation, ride alongs, and lots of track time... I learned that he wasn't so much out braking me or waiting later.. he just wasn't braking at all really.

Now this is certainly not the case on every corner, but it is true on some of the fast and some of the slow corners... for example:

pueblo corner 1 (I know this means nothing to you) is a 1/2 mile straight away, and then a 180degree 90mph corner. I used to try and stay on the throttle until I saw my braking point.. then I would slam onto the brakes and turn in. My buddy who I'm referrencing would close up on me during the turn in like mad. NOW, I've learned..... this is a trail braking corner. Instead of slamming on the brakes and dragging the car from 120mph down to 90mph and turning..... I turn at 120 and then trail brake down to the apex.. I can catch 5 car lengths on people in this corner just between the turn in point and the apex. Its an entirely differnt line on the turn in to make it work. I still am about 90mph at the apex, but most of the speed is being scrubbed by the turning of the car and the (holy cow did he say that:) LOCKED DIFF, plus a little bit of dragging of the brakes... When I do this, I'm not pushing very hard on the brake pedal and its more of a dragging action than a braking action.

Thats a fast corner, here is my experience in a mid speed corner. Take corner 10 at pueblo. Its a 90degree right hander, big wide, and about 60mph. I used to go up to it.. brake and down shift to 3rd then gas it at the apex and start the eternal wait down the straight away before the above mentioned corner 1. NOW, I leave the car in 4th, coast a little bit at the turn in, and then coast towards the apex while scrubbing a little bit of speed on the turn in... NO brakes used... then ease into the gas and start the straight away.

I used to watch cars go through lots of different corners and not use their brakes.. (or not light their brake lights)... I've learned that I had to change my lines/turn ins/ and corner style to make this work for me.

Slow corner: I brake.... I also scrub some of the speed at turn in with the car. I've never over heated those vented rotors... however the same fast guy I keep referring too (dale tutey by the way). I don't think he has ever overheated his stock rotors either. I do know that he has simple dryer duct tubing dumping air into the front leading edge of his caliper....

I'm not going to claim to know what your 210hp motor would be like at the end of a straight away. I'm also not going to have any clue what brad's old tube frame car was like at the end of a straight away. I'm sure that hp changes things a bit, on the other hand the fellas I know that run 1900lbs, and twin plug 3.3 electromotive engines... don't seem to be on their brakes that long, and still run my same trail braking line in that big corner 1.

I think that my experience on the track with a 914 has taught me that the trick to going fast is not using the brakes.... I have tried faster and faster motors with more hp, and always was disappointed that I would hardly pick up any lap time... then I feel like I came to realize that the lap time would come down by focussing on this use of brakes more than any other aspect of the driving..

Wow, I didn't know I could write a whole book...
have a good day all
brant

Just my $.02, but I'd rather have the solid stopping power of my BMW calipers up front and the rear proportioning valve removed when driving on the streets. When the Dumb A$$ in an SUV or new lexus cuts you off in your old school 914 with your stock brakes from 1970....good luck stopping.

It's a safety issue with me being able to stop as well as the car in front of me on the street. I'm not talking about racing for 12 hours with this set up, just an affordable solution for the street driven 914.

Oh.. Oh... oh.. (horseshack impression)
I wanted to add another thing too..
When stock brakes are rebuilt for street use with good pads (don't have to be race pads).. they can work amazingly well.. Bleeding is a big key to this, but wheel lock up is easy in a well set up system on street tires...

and once you've locked em up... what more do you want.

brant

Yes, lockup is easy!

on blue car I had a 19mm with stock 4 parts front and rear. So damn easy to lockup on the street. I almost bought a couple cars in front of me cause they locked up easily.

A BIG BIG BIG factor here are tires. I didn't have the right size & compound tire to stop. -4 Brakes on a -4 car are more than sufficient when setup correctly. Unless your car is repowered or a big track car I don't see the need for more brake.

-4 tires are sr165 I am going to a performance 205. Are stock up to that? Post experience. I agree that tires are the most
important factor in the equation. With the better tires I would think the bmw units would be ok Yes?
Also, I have heard that one of the problems with the vw stock stuff is that they flex. I do not know if this
is true or not. I think that what works for racing might not be good for the street. This is where I feel a lot
of people are coming from different schools of thought. Race pads, tires and the lot need a particular set
of circumstances to be effective. That said it the zone they rock. On the street in the rain etc. they become
dangerous. I can never find my pit crew when it rains
I guess what I am saying is that you have to take your needs into consideration when modifying.

I ran the previously mentioned setup at the track with 205/15 BFG R1's (sticky tires) and it stopped really well. I didn't ever lock them up, but I didn't try to

Brant, can I quote you? That was very nice!!

--DD

Yup - when that happened to me the other day I locked up all 4 wheels, like a dumb shit. With stock brakes.

I just installed boxster calipers with vented rotors up front, with carrera (M)and vented rotors in the rear. Not because i couldnt outbrake almost every car on the track, but because I wanted expanded heat reserves for longer sessions/enduros and the ability to expand the motor size without having to update brakes. We have had this issue brought up many times, the main distinguishing variable has always been the application (street vs Track use). The key of course is to not use your brakes on track ( ), and apparently have back breaking decel on the street ( ).....