Hi Sean, So how is the brake cooling work panning out??? I am trying to improving my dad's old 911 brakes, (same piston sizes ironically enough, 48-38). Maybe going to front cooling ducts and EBC yellow stuff pads. One huge advantage the "dark side" enjoys is massively more people focusing on improving the car, so there are several brake cooling systems available, many more brake upgrade options and a huge customer base looking for improvements. Any thoughts??? Dazed and confused, chris
The cooling ducts are working excellent ... so well that I shelved the big brakes for a few months. I'm running Portefield R4 pads ... race pads ... they like heat and have a high friction coefficient once they're hot which my sticky race tires really like . On your P car I would experiment with better pads first. My second 308 has brand new brakes and rotors on it but the difference between how that car stops vs. my Alpha 308 is night and day. It was instantly apparent why people think the 308's brakes are so weak when I drive that car, but the only real difference between it and my other car is the pads in terms of initial stopping power. Even with some old TRX's on 'er she did not want to lock the front wheels up very easily. With good pads it's night and day ... so try pads first before spending a bunch of money on brake upgrades. My '73 911S has bone stock brakes but that car is light!!!! ... and you can feel your heart pushing on your rib cage when I brake hard with that car ... she's got some racing Pagids and racing slicks ... stock calipers, cross drilled front rotors, slotted rear ... thats just what it came with from the po. On a side note I'm going to start autoX'g with SCCA I think. There's an event this weekend. My car falls into a class where I think I can be pretty darn competitive at the national level but we'll see. cheers
Saturday or Sunday at Qualcomm? Maybe I'll stop by with the camera and get a few photos of your car in action and say hello.
Hi Sean, My 74 is about 2400 lb. What pagids are you using?? I have R4-s on the 308 and they are good cold. The 911 is mostly a DD, so i can't have a pad that doesn't grip cold. Do you have any experience withthe EBC yellow stuff?? I heard that Martin at Girodisc recommended them for rears to the guys running the Brembo big brake kit to try to make up for the heavy front bias. chris
From memory I think the Pagids on the 911 are orange if that tells you anything? ... haven't had to replace a set since I've owned 'er. They are pretty bad when they're cold though. Martin cautioned my about the race R-4 compound on the street vs. the R-4s, but I would say when cold the brakes are like my beta 308 with "I don't know what pads" for brakes. Before just diving into the "yellow stuff" (never used them) most of the brake pad manufacturers list optimum temps and coefficients of friction cold and hot. I would compare those spec's before making a decision ... HTH cheers!
Saturday is practice and Sunday is the official timed sessions. I'm thinking both days but if I'm not as fast "as I think I am " on Saturday I may not be back Sunday . The tracks they setup for SCCA are a different animal to what I'm use to with PCA. Much tighter and lower speed which is real problamatic for oil starvation even with the updgraded baffle and TWO extra quarts of oil ... see ... already have my excuses ready!!!! If that is a real problem there is no way I will go back on Sunday. I've had that problem at the Porsche club before which is why I'm kind of selective about when I go run with them. I prefer counterclockwise setup which means more left handers than right . I think they know this because lately the tracks have been all clockwise . cheers!
Are you sure it isn't NEXT weekend? http://www.where2race.com/events/view/846-scca-san-diego-national-tour
I was playing in the mountains last weekend with some bikes and my brakes started fading again. I thought it was because the pads were getting too hot but after chatting with a P car racer/mechanic I'm thinking all differently now ... he told me if I was running race pads it's probably the fluid, and I'm not running fresh Motul right now. It's old ATE blue. I checked the temp of my rotors and they were about 600 f in the middle. The shiney surface of the rotor where the pads run throws off my pyrometer so when I say in the middle I mean where the pads don't run ... the hat part of the rotor I guess would be the term. I thought that was hot but after looking at the temp charts for the Porterfield pads I agree with the P mechanic that it's probably the fluid boiling. It was very interesting that it felt like pad fade, but I guess it could've been there just was not as much pressure/force from my foot reaching the caliper. Something else he said was "You want heat in the rotors and pads, but not in the caliper. If they're the same as the P car caliers there's ceramic insulators you should put behind the pads to insulate the calipers". So this got me thinking that my ducts really need to be pointing at the caliper and not the middle of the rotor? Looking forward to a brake flush and another "test session" . Any more thoughts from brake guys? I put thermocouples in my pads but I don't have my data acq going all the time 'cause they only got to like 600 f when I first hooked up the ducts. I wasn't breathing hot gasses from another vehicle but I was trying to get them hot ... coming down the mountain accelerating and overbraking almost to a stop so the fade last weekend caught me by surprise. I'm really interested in figuring out what is causing it. It's amazing the temps the pads and rotors live at. Cheers all! Sean
Hi Sean, If your pedal is firm, (as opposed to soft or long), then it is the pads. I have had the embarasment of driving fast and feeling the pedal get softer and spongier as the fluid, (or more appropriately, the moisture in the fluid boiling),. Get the air to the center of the disc and provide a block off plate, so the air is forced through the eye of the disc and out the vanes of the rotors. Just aiming a duct at the hot stuff is not the most effective use of the air. As i recall, you had some nice front air dam ducting. Here are a few of the DarkSide parts to achieve better cooling. hth, chris The little sales blerb on the Ti insulators said that the Ti transmitted about 1/7th asmuch heat as the steel. Our rotors are solid, as opposed to open like the porsche stuff, so the first photo of the block off plate is meaningless for us. These kits hang the scoop under the front a arm, which is not olnly perilous but not as effective as a out front duct opening. Note the attempt to get the round backing plate as tight to the rotor as possible to keep all of the air going through the rotor, to better extract the dreaded heat. Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
Thanks Chris ... those guys have all the goodies worked out don't they? It's just such a shame that nobody in the 308 world seems to have seriously blazed this trail. What amazes me is the dark side cars from that era have essentially the same brake calipers and they race the heck out of 'em, so why do we have the problem and "reputation" that the 308's brakes are so lame? We are carrying "roughly" an extra 400 # but I'm not braking from over 120 mph. Probably right at 100 mph but I'm going down hill ... should be nowhere near a real track day that the P guys run. He did tell me pads with atleast 50% material are a must or the P cars boil the brake fluid. I've got plenty of pad. If the only difference is the floating rotor I would play with that, and that is specifically what I asked this P car guy about. He told me that shouldn't be an issue because the race pads will go over 1200 f ... adding the fact that "We'd see rotors glow on the old 911's ... you're not pushing that hard". I was nowhere near that temp on the rotor or pad, so it makes sense. My rotors are blue though and some temperature paint would also be priceless to understand really what's going on. Your comment about pedal feel is exactly why I thought it was pad fade, not fluid boil. The pedal still felt pretty firm but I stopped pushing really hard as soon as I felt the stopping power decrease. There is zero run off on the mountain . It is gonna be a simple test to flush the brakes out and put in some proper fluid. I was hoping for some "that makes sense" posts .... anyone? Thanks for the input Chris ... I could call Martin and just get to the bottom of it I guess. cheers
I always understood that if the pedal goes long then its boiling fluid, if it just feels solid/wooden accompanied by a loss of braking then its the pads overheating. New fluid can't hurt but I'd look at what the limits of the pads are & how you can introduce some more airflow into the area.
Yeah thanks. That's what it felt like but again I go back to the fact my rotors were not glowing, nowhere near that. Regarding limits of the pads I've attached the curves from Porterfield. I'm running the R-4 compound. It has more stopping power at 1300 f than R-4s pads have at peak operating temp. I'm finding hard to believe that my rotors or pads were anywhere near that hot. As mentioned earlier I've got a thermocouple in one of the pads ... it's sounding like I need to do another run with a laptop flying around in the passenger seat or invest in a basic gauge of some kind for the TC. cheers!
Well, as they say, if it walks like a duck..... I would either be looking at a different pad compound or what you can do to introduce some more cooling. Have you got any scope for larger discs (rotors) on this car?
Hi Sean, The 911, (at least my 74) run a 48mm front caliper piston and a 38mm rear caliper piston, just like us. My dad's 911 weighs about 2400, whereas the 308 with me and a half tank of gas, comes in at 3400 pounds The 911 has no power assist. I think the reason they get away with this f/r hydraulic pressure balance is because they cary significantly more weight on the rear, it is lower and they do not have a prop valve. My best guess is to go with more air to the fronts, with a plate fitting close to the inboard eye of disc opening to seal inthe air,then get a hose fromthe front to feed in the air. As with most things, a bigger diameter hose is better and of coarse the hose will flow more if it has the least kinks Second, go for a higher temp rated pad. hth, chris
I've got a design for rotors with a seperate hat. I was thinking I would spec out a rotor with directional vanes and this is what right away got this P guy telling me worry more about my brake fluid and insulating the pads from the caliper. The pads and rotors "want" to be hot, but not the caliper. So when we get talking about more air flow, I guess it makes me wonder if the air flow is preferred over the caliper vs. the disc. I've seen drawings showing the ducting concentrating on the rotor but it got me wondering if those are required for tracking where you can get the rotors over 1300 f ... maybe? ... going down a moutain fairly fast where the speeds are really only around 80 mph braking to 40 kinda thing just doesn't seem comparable to what a P car sees on the track for continuous lapping and hot exhaust always coming in the brake ducts. It's only 7 minutes each way up and down so the brakes get pretty cool going up. Regarding P car weights, the earlier cars I agree are lighter AND my S has aluminum calipers which are able to dissipate heat quicker? The later 911 SC which is what I thought had the same size fronts and maybe slightly larger rears weighs almost 2600 #. I just weighed my other 308 and it's 2950 # without the battery but with both bumpers which add 80 #. Yes the weight is a key factor but the energy that needs dissipating goes up with the square of the speed. I got the feeling that the speeds the P cars hit on the big tracks would be comparable to the heavier 308 on the street. Thanks for the input gents ... I'll post back after the fluid flush and see if I can get some real data vs. just my interpretation of how the brakes are fading. The pedal very well could've been getting soft vs. hard and not really stopping. I think when it first starts to happen it's not as obvious what's going on ... maybe? ... or is fluid boil always obvious and a mushy pedal will be there after the brakes cool down. I was thinking I was right at the point of boil which is why I didn't go to full mush on the pedal. This P guy I respect otherwise I wouldn't beat this to death. I was ready to get into some rotor R&D to get rid of more heat, but he didn't think I could be overheating race pads. cheers edit: regarding proportioning valve, I thought I read in another thread that the 308's do not have a proportioning valve, and I thought having or not having power brakes was purely a master cylinder and pedal box design balance????
The pads want to be hot - upto a point, beyond that they do what yours are doing. Going down a mountain you are dealing with (relatively) lower speeds so the airflow/cooling on the brakes is maybe not as good as at higher speeds. At the same time you are dealing with not only the forward momentum of the car but the added momentum attributable to gravity i.e. the braking force needed to slow the car from 80 to 40 on the flat is aa good bit less than when travelling downhill. When you add the two together over a resonably long run I can see how the brake temperatures will gradually climb out of the "working zone" Ya just need bigger brakes!
Continuing to beat a dead horse . 1. I think P cars ran our front brake pads all the way to 1989. Those cars were not that light! 2. Rounding the weight of the car to 3000#, a decent of 1000 ft is 3,000,000 "Energy Units" (BTU's or something ... I'm doing this fast ... formula: energy = mgh). Equivalent energy from speed (1/2 mv^2) ... approx 120 mph ONE time ... I'm not buying that as being a significant amount of additional energy to absorb. I would guesstimate we decend about 3000 ft in 8 minutes and my brakes started giving up after the first 2 minutes. So based on this I took a look at my front calipers and found the right front was getting way way hotter, and the pads are wearing crooked and are significantly worn! Okay! ... hopefully all the heat was due to a sticky caliper. I rebuilt that caliper and squared up the pads but I could really use a new set now. How time flies ... I thought I'd replaced them recently but looking at my log it'd been 125 hrs. So one more time ... why are the 308 brakes considered so lame when Porsche used these pads all the way up until 89? The reason I'm not just finishing my big brake upgrade that I started in this thread is because the lack of a brake bias made me realize I am going to have to do a lot more to get the balance back. I'll finish that project eventually. I think the stock brakes can be made to work when playing at less than triple digit speeds ... again ... just basing this on the fact that the P guys run the heck out of their cars ... just no comparison to the street even if it is a mountain grade based on my napkin calc's ... what do you guys think about those energy numbers? ... pretty insignificant I think? Also ordered some temp sensative paint to put on the rotors and some indicating stickers to put on the calipers. After doing a bit of research this is brake R&D 101. After a few mountain runs I will positively have the data I need to determine if I really need the bigger brakes (edit: or just a better rotor/slot the rotor/insulate the pad/more air flow/all of the above ) cheers
Hi Sean, I have noted that every car, 246, 308,328, 348, 355, 360 and even some of the faster stuff; guys complain about the brakes going away on the track or really fast street driving. Same thing on the porsche forums, (well not all of them, i am just getting into them). You are right, fast driving, particularly down hill, where you have more kinetic energy "on" your side is more demanding of the brakes. Basically, you are converting kinetic energy into heat, that is all that the pads and discs do. Even driving down hill, semi fast, (my wife doesn't do G's well), i started to Pad fade the brakes and noticed more pedal pulsating, like the rotors weren't likeing it and warping. You can help them get rid of the heat with more air or more surface area, (bigger discs). If they are going to work at elevated temps, you need pads that can maintain friction at that temp as well as brake fluid up to the task. Have you noticed how fast that pads and discs wear at elevated temps, one or two track weekends and some guys are replacing discs and pads, (a few hundred miles) and i bet they are having to back off at the end of the straights once the brakes are on fire, just to save their ass. So, to make the stock brakes work, big ducts, hose and tight fitting plates to keep the air going where you want it into the eye. High temp fluid. Pads that can live at high temps. My 77 for sure had a proportioning valve, i took it out and installed a lever type tilton adjsutable unit. If you take the (early) Porsche way, you size the calipers for proper balance at max decel with street tires and give the sizing a margin oferror and you get 48 front pistons and 38 rear pistons. Keep in mind that the 911 engine has a lower center of gravity and hangs out the back, as opposed to the higher, mid mounted 308 lump. Most manufacturers utilize a prop valve to get the back brakes to do more of the work slowing down, then use the valve to start to restrick the pressure as weight transfers to the front. I kind of like this approach because it makes use of the rears more and gets the temps up, so that you dont have semi hot front ads and cool rear pads. With the temperature gradient v coefficient fo friction, i think this can lead to erattic braking. The one argument that i have heard about using a prop valve is that it induces a bit of "hysterisis" ,(Carroll Smith, my Hero), which i don't understand, but if you said that the prop valve, because of its nature, (a spring loaded piston) gives just the slightest bit of softness, I could understand that, but i don't feel even a bit of softness in the big 308 brakes. I have attached the spreadsheet that Martin at Girodisc used to get the proportioning close with the parts I had. We played with 360, 355, stock, and F-50 calipers. Check out the numbers As Mad Dog as you are, i think you might be able to use a bit bigger front rotor and more air. regards, chris Image Unavailable, Please Login
Hello LuckyDynes,Ive heard a lot of great stuff about your cars and projects.My mechanic says its the rear calipers that are no good and dont do much,and that they end up dragging.He has a lot of experience and says its the right rear that drags first.Were wondering how hot are those rear pads and rotors getting? Reg says that the P's really sit on their asses when the anchor goes over board while 308 want to flip you out of your seat over the windshield.I dont have a car yet but I need to figure my budget.I really enjoy FC.
Hi Austin, I have had two cars with the ATE rear calipers, my 77 and a 914 that i had for 20 years. My experience has been ok. They are fiddly to adjust, but i have never had a dragging or sticking caliper and i abused the 914 brakes something fierce on high speed auto x, ignored fluid changes, (i have since gotten religon) and not had any problems, other than stinking/burnt pads and an occasional soft pedal from boiling the water in the fluid. They are asked to do more work on the 308 but they are ok for street use. By way of comparison, both cars, (77 gtb and 74 911), have 48-38 mm pistons for a static brake balance, (ignoring slight rotor diameter differences) of 61% front and 39% rear, however, the 308 has both a proportioning valve and a power booster because of the higher weight, (800-900 lb) and better weight distribution, (44/56 versus ~40/60 F/R). Both cars have significant forward weight transfer under high G braking. As has been stated many times before, the difficulty getting bigger brakes on the 308 is dealing with the rear caliper replacement. Brembo makes a bigger front set up with 36-40 front calipers and bigger discs but it does not address the rear brakes, hence, they are not proportionately effective as the fronts. Next step up is the Girodisc Brake upgrade which utilizes bigger front discs and IIRC, a wilwood caliper that has pistons somewhat smaller than the Brembo, so the F/R balance is closer to stock. Additonally, Girodisc has floating rear discs for an improvement in weight and brake cooling. Some have simply abandoned the e brake in an effort to upgrade front and rear brakes. A slight improvement is to use a "Hydraulic Lock" on the rear brake line. Staying within the Ferrari family of Brembo brakes, the 355 uses 36&40 calipers, the 360 uses38-42mm pistons and the F50 uses the 40&44 mm whopper. Porsche, onthe other hand has used a lot of different Brembo calipers with smaller pistons sizes, (which i do not have at hand) and it probably makes sense to look within that group to find sizes that offer better balance. The stock ATE iron brakes are heavy but they work fine for even spirited street use, Rabid, MAD Dog downhill racers, (who shall go un-named might benefit from more rotor to dissipate the heat. As an interesting side note, the new front caliper and 14 inch disc assembly weighed LESS than the stock parts. The rear brakes, including parking brake, bracket and pads weighed about 5% more. There was also quite a bit of work adapting a wilwood MC, (i should have used the testa rosa unit) and a prop valve change to fine tune the balance. Even though they are lighter, i am sure that they have a huge amount more rotational inertia. The bottom line is that the brakes are rock solid, dead linear and bullit proof. chris Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
Hey Gents, Thanks for the input gents! I am happy as a boy could ever be after a morning test session in the moutains this a.m. So to summarize, rebuilt front calipers, squared up used pads, flushed brakes, installed heat stickers on the caliper (420 f - 480 f) and heat paint on the rotors. The heat paints are the following temps: Blue: 750 f Red: 1000 f Yellow: 1200 f The pic's tell the whole story. I had zero issues this a.m. but I was not huffing hot cycle exhaust gas. I was being very aggressive on the brakes ... way over braking so based on what I'm seeing I'm fairly confident my brakes will be a non issue. Also, my rotors are nowhere near new so there is even more heat capacity there. Chris thanks for the detailed response and info on the P car parts sizes. I need to follow thru here and look at the actual piston size on the fronts and rears of the 911 thru 1989 'cause those cars do not have that much of a weight advantage. The concensus is the 308 brakes are "weak" but for 99.99% of the owners when setup correctly they are more than adequate IMO. F1austin ... my problem I think was very similar but now that I have rebuilt the calipers I am not sticking at all! Looking forward to another run with the bikes. I included a few pics of what my tires were like for the autocross and run in the mountains last weekend ... talk about night and day on turn in again ... WOW!!!! I got all the way down to the little arrow on the sidewall ... there is(was) a ton of rubber out there. cheers all edit: Jeez Chris ... you're giving me brake envy 'cause I know "size matters" ... saw this bumper sticker: "If size doesn't matter why am I so popular?" Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
Had no heat issues this morning. The 1000 f paint didn't budge and the stickers on my calipers did not register. The rebuild of the calipers has made a world of difference. According to GPS the decent to the base is 6.75 miles, 2400 vertical feet, and I counted 33 corners on the map my app saved. I'll still do the big brake upgrade one of these days. The stock brakes with good pads and fresh air are able to withstand what I throw out at 'em ... for now at least. cheers
