KaiB

Bias....nah, don't need to get it right.

Dang, this thread has gone Kibortian now.

ir_fuel

So ....

extra cooling wont help because you think the problem is that your brakes get too hot by the end of the braking zone?

Maybe you can install a few 120mm computer fans in front of the discs so you get enough airflow in the slow speed part of your braking?

Time to get my coat ....

mark kibort

Hey, knuckel-head, dont derail a discussion just to hear yourself talk.

brake bias is another animal all together, in which i would like to experiement with too. And for your information, ive owed many of my racing wins out of guys that have TOO much bias. love to see that trail brake rear end step out in a heated battle. I will admit, i have very little, but is it the reasons that the fronts over cook? I dont see how, since the fronts will be punished to the limit of grip of the front tire.

I did an experiement with fuel cut off at off throttle, and that compression braking under decel was greater with fuel cut off than with out it. it was enough to step out the rear end at turn 11 at laguna. when i disabled it, this problem went away. one can only guess that with more rear bias in my car, that the problem that i dont want, might return. Hey, I have no problem testing it out as the bias might be an easy change and test.

the fact still remains that under 2g braking (and the wheel base and ride height) that only about 250 lbs will be under each tire. how much can 500lbs really slow down, and would it be enough, if used to its max, to not cook these 12.6" rotors under threshold braking? I get a significant amount of brake dust during each session with pagid black RS14s in the rear, but certainly the wear is much less than 4:1 vs the fronts.

KaiB

You give me far too much credit Mark....

I get it. Your front brakes aren't doing whatever it is you want them to do.

Why not merely do all the same stuff everyone else is doing, doing it right from scratch on up and then ask? I honestly believe you are the one who tosses this crap out into the either for the sole reason of creating another 9 page thread which goes absolutely nowhere.

mark kibort

all joshing aside, i was involved with a nascar project that used the eRAM for braking assist during qualifying. (also used by nascar trucks for downforce in venting air to the rear "bed" area) . in the braking assist, the fans did a good job of getting more heat out of the rotors. they would use them in qualifying and burn up the electric motors. but they worked. the name of the team was very well known by the way........ oh, the fans on each side was near 1000cfm. nice blast of about 100mph air flow out of a 3.5" fan.

to your question.... what im saying is that when i did tests to start out much cooler than any ducting system would help create during a hot lap, (by not using the brakes for a lap), the problem still existed. i could try and do this for several laps, to get tires warm, but no heat in brakes, and then try it, but i think the result would be the same. the point is, the heat issue is at the end. the question is can a 3" duct, at 130mph to 60mph over 4 seconds , take away a few hundred degrees out of the rotors to make a difference. Do you have the answer to this question? Intuition tells me (and i ususualy blast folks for using that here in discussion) that in this condition of grossly overheated brakes in a very narrow zone , might not be helped by air ducting to reduce the fade. I dont know, i have to try it. I can heat up a rotor and blow 1000cfm at it through a duct and see what the temp drop after 4 seconds is though for a test.
Again, ill be ducting up some tubing to have something ready for Laguna next month.

mark kibort

Because it goes back to the original post and question. an "expert " say's that i bedded the pads wrong and I dont have enough rear bias. I personally think the 12.6" rotor just cant do it. IM thinking out loud here and using some knowledge in the discussion. its a discussion! If anyone else has done it, i would like to hear about it. personally, i havent seen it. I have no reason to fight the posts from anyone that just wants to jump to a conclusion or make a joke out of it. Some of us do not have unlimited racing budgets and need to make what we have work, as well as we can. We are the pioneers in some ways, by not just getting a bigger hammer to go faster. Smarter , sometimes goes faster.

Sure, if i wanted to go faster than anyone else, I would just by a '14 cup car and call it a day!

Part of the racing for us that are not pro's, is to figure it out and do with what we have better than the rest we are competing against. if you disagree with that spirit , which is the spirit of the question, than just dont post or engage.

It constantly amazes me the discussion the list. Ive said it before, its easier in a bar, in the paddock with a pen and a napkin. Normally, anyone not wanting to discuss or partake, would usually just walk away. but for some fascinating reason, some feel a need to blow their horn, make rude comments, for what i see is ironic, based on what you think Im posting for, in order to hear themselves talk and get a few cheap laughs for a put down. Think about that before you respond.

For me, for the majority of interactions, its a hell of a place to learn. Ive built race cars, got to be a better racer, and solved all sorts of problems due to interactions on this list in a discussion. this is yet another of these discussion. If someone had run 12.6" rotors/small calipers, and run a 1:36.1 at laguna without fade down to turn 2, i would be all ears and do exactly like they have done. Until that guy chimes in, im logically thinking about how to make these rotors do something that they might not be able to do without bigger calipers and pads or better cooling. I'm challenging the ideas because the physics is stil the physics and some of it doesn't seem to add up. there is no free lunch!

KaiB

322mm front rotors work on all kinds of fast cars.

I know for a fact that one not so very light air cooled car runs in the .31s at LS, with 322mm rotors and has no problems whatsoever.

kurt M

do you have the fade issue on the first lap? Heat added up with each braking cycle. Less heat at the start of the braking cycle the larger the thermal intake before the pad starts to oblate and float reducing torque. Your car the track and the like are not out of the realm of normal. The answer is a good mix of the right pads, prep methods, and remaining inside the thermal range for the equipment. To have consistent "fade". Issues and to dismiss increased cooling is silly ( not a put down).

I have seen where even basic improvements in cooliung corrected a host of braking issues. Use a high torque pad but keep in mind this will increase the thermal requirements.

If it seems that I put you down a bit it might be after watching so many Kibort threads go to hell in the same way.

What cooling over stock do you have now?

winders

Mark,

There are to major issues I can see with having too much brake bias to the front.

1. The front brakes are doing too much of the work stopping the car and overheat.

2. If you are trail braking, what happens when you have too much front bias? I will let you ponder this one. Think friction circle.....

I am pretty sure this problem would be mitigated by adjusting to a more appropriate brake bias ratio. My race car is at 1:1 and I trail brake all the time. I know, my car is way different than yours....but I think you are thinking about the bias ratio and your use of trail braking the wrong way. If you have too much front bias, you can't trail brake as well as if you had more appropriate bias.

Mahler9th

LOL, I know that car and driver... pretty heavy car compared to mine.

Instead of cutting holes or slots under the driving lights, I would consider removing the lights and attaching the largest NACA ducts you can, to collect air for cooling. As large as you can. Here, size is everything.

This is what I did to my 951 (which had a similar front bumper to your 928), and I did it in such a way that I could easily reinstall the lights for commuting. I got this advice from a contact that was running what was effectively the US Porsche factory team at the time, and it worked very well.

While in some situations/circumstances it is possible to have too much cooling (that is so much that lap times are affected in a negative way), that is untrue for any 928 or similar Porsche.

I suggest that you be aggressive and creative to optimize the cooling.

Some day I will get to listen and poke fun while you and Scott are discussing theory related to running sub-50 second 400's. Or given your ages, sub~48 quarter miles I guess. For example, curve running strategies and braking forces after you've stopped the clock.

333pg333

Hmm, I don't think I'll jump onto your 'lightening will only make it worse ship' Mark, although there'd be plenty of food to go around. You might be going a bit faster but your retardation thingys would be working with a lighter mass. Further to your equation...ergo just keep adding weight until you are going so much slower that the car doesn't actually reach double figures. It would be like Steam roller racing.

btw, contact Coleman directly. They made both our Hats and Rotors (although they got a little confused when converting mm to inches) however in the end they did the right thing and sent us some replacement rotors the right size. I dealt with Lary (with one 'R').

As far as evacuating air out of the wheelhouse area, it's all positive. 'Wheelhouse' was a term I was unfamiliar with until we had a 2 day consultation with a US Aerodynamicist. We have increased our front downforce significantly by following his recommendations. Sounds like you've begun doing same. Being an Aero guy, he didn't want us to go up to such a large rotor as that will block some of that evacuation...but we did anyway and are happy with the results. I thought it would have a noticeable adverse effect by increasing the front inertia significantly, but nothing noticeable.
(Note, this is not a kiddy car. Currently 1/2 a second quicker than the lap record for V8 Supercar on a 60 second track.)
You should continue to vent and build a proper splitter. This will all help braking and racing in general. See how much we have opened up the rear of the fenders and also angled the rocker panels.

mark kibort

I know there are some fast cars in the lower 1:30s, but usually they are very light, or have a lot of HP. I dont consider my car a momentum car, but compared to the competition i run with , it is. so, i end up cooking the brakes when i can.
Its all good information. just spoke to one of the old BMW competitors and friend of mine. I wanted to know his brake package. 285rwhp and the stoptech ST40s. great comparison, because we use the same small pad. he felt very suspicious about he ducting craziness of all the other competitors, but when he did it, it was amazing. (on his prior single piston caliper set up) with all the bolt ons, his brakes were pretty amazing. Hawk HT14s and lots of ducting. I know we were running a little slower back then, 1:38 high, and he was 200lbs lighter, but i think it is a good testimonial. and ive driven the car, its pretty stout.

Ill put a few pics below of my set up. probably the best of the brake air flow deflector set ups, but its pretty crude compared to you guys ! since i dont have a lot of experience with ducting testing, you tell me how much better the true ducted technique will be.
to answer your question, i have fade at that one part of the straight at laguna before turn 2 and thats it, and it happens regardless of brake temp it seems.

good point regarding trail braking, but i have enough to get the rotation going, but maybe a little more might help and also help the straightline braking as well. something to test as well.

to your first point, i still think you will end up with using the front brakes to the limit of the tires. now if the rears can slow the car a little sooner, certainly , you spend less time in the fade zone, or maybe stop miraculously shorter as to not get fade.

Ha ha ha!! (regarding the the track stuff! )

Yes, your right. in fact Anderson in his monster 928, had the brake inlets in the fog light area. good idea to just carve that out, as like you say, i can make the light area adaptable for both a duct or the light. however i do use the lights on the street sometimes and on the track, and i dont think two holes in that area would look that bad. heck, already cut some of it out for the increased radiator venting. by the way, that was AMAZING as far as lowering water temps!!

Sounds like a monster ! yes, im an aero guy to as you know, and the hood venting based on aero pressure charts of the car from the factor, helped with the design. definitely, wanted to do the fender vents!

Ill talk to coleman again. maybe just have them make the hats, and HOPE that i can raduis the calipers AGAIN to fit 14" vs the 12.6 i have now. i had to do that for 11.9 to today's diameter and thats not fun grinding on the brembos! should brake down and buy a big brake kit. thoughts in the works though , thanks.

as far as weight. yes, lightening can put more demand if you can get a higher speed to the same percentage as you lost weight. in other words, 4% lower weight might make a 4% higher speed, which is 8 % more kinetic energy. so, that can be a problem.... but a good problem to have, right???? The only problem is getting to slow the car down, and if you are in fade, well expect more of the same!

mark kibort

some pics of the modified. (modified with the splitter, integrating the brake air flow duct entrance, but no tubing, and some guide deflectors that direct air to the rotors at the hub region. )

Veloce Raptor

That's it?

That's your front brake cooling?

Well...Mark...for the 10th time in this thread, it is plainly evident that this is the entirety of the problem you are having: inadequate cooling.

mark kibort

thats it! And has been like this for many years. good for road america, willow springs, buttonwillow, and many others, but no good for running up to turn 2 at laguna. So, consensus says cooling. Ill duct something up and expect some results!
Thx for the inputs.