mark kibort

Thats exactlly what im doing. However there are those here that seem to be missing the closing lines of almost all the posts, where i say, "im goint to test that out." I have the brake ducts on order, getting the bias bar changed out to double and then soon figuring out what temp paint range to buy. so, im doing it alll , in hopes it will change things.
the reason ive argued the physics of it, is because by understanding what is more likely to work, you dont spend time doing something that doesnt.
the side bar argument about making the car lighter, is an interesting one, because the physics is pretty clear here. going lighter helps slow faster, but for those same reasons it helps braking, it helps acceleration. so, if you end up faster, there is likely to be the same KE stored in the car to have to slow down. the only thing that saves the opposing argument , is if your turn in speed is higher, you might be better off, but slightly. we all know going lighter is better and ive already carved as much out of the 928 that is possible. The only thing left, is to strip the car and sand blast the chassis for the last 150lbs like anderson did, but then he had to put in 50lbs more bars to stiffen things back up too.

Im running 4 square now, and what a dream change that was. I lose very little on the 3 lbs heavier front tires, (another discussion if you remember a while ago ), for obvious physics reasons, AND, with a big honkin' tire up front, all that rubber is a great safety net for overbaking a turn entry as you can just turn the car in and use the push to slow the car down if you run out of brakes! Unfortunately, now when i have to go back to a slightly smaller front tire, im no where near as fast as i used to be.
I only use the smaller front tires, when those freebies where givin to me and were slicks. i seemed to like the larger DOTs vs the smaller widthslicks. i had a great test day set up with two back to back races, and then i had electrical issues that force me to get towed in on the DOTs to see if i could match the race time. But yes, normally , on the big front tires when ever possible.

My car sits at 56 /44% front to rear weight distribution. the 928 has a lot a junk in the trunk when making it a race car. cross weights are awesome, but most of the weight is now in the front. so, more the reason i dont think the rear bias change will help much, but im willing to try.

333pg333

I can't argue the physics but I would think that by going lighter (and it sounds like you've done a fair bit already) you will be going faster but you will hopefully be able to benefit from the lighter mass to pull down to the appropriate speed to make the next corner. To add, by rights you should be able to go faster around that next corner too. Because you're going faster you should be able to brake for less time. You might be able to use less pedal pressure due to the shedding of eg 200lbs too although this may be made up by the extra speed needing extra pressure to compensate. Not sure just where you stand after all is said and done. By increasing Aero efficiency you will be able to turn in and corner faster as well. Contrary to most advice in here about ducting, we've removed ours but that's because we don't run for very many laps and our splitter directs a lot of cooling to the inside of the wheels. You could improve your splitter 10 fold and run some under car diffusers without spending a bucket-load of $$ on it. This might allow you to run more AoA in your wing which while increasing drag, also increases downforce ie faster corner speeds. This is the key to faster laps in most cars. Not nearly enough attention gets focused on Aero at this level of car.

mark kibort

Well, that was the entire argument on the one topic. (lightening the car is easier on the brakes". This is not a solution, because of the simple fact, you will be going faster if the car is lighter, and KE is more weighted dependent on speed, NOT weight... so the faster you go, the more energy you need to stop, and you are going faster due to the lighter weight, just as you say, its easier to stop... right? you are not going to use less pedal pressure, because you want to stop to the limit of your tires. Many of the points made so far, are based on comparing to the prior,, "problem" set up. We are trying to improve the brakes, solve the overheating problem.. By going faster by going lighter, can improve the lap times, but not solve the overheating problem of the rotors. Just remember, power is the rate of change of KE. energy required to stop is the difference in KE. And as you know, KE is just related to mass and speed. doesnt matter how you get there, if you are there your KE is determined. slowing down, just exchanges speed for heat.... its that simple.

So, the point is, yes, we all want our cars to be lighter and Ive done as much as i can over the past 10 years on the chassis, but we want to solve the overheating problem and that means dealing with the KE that it takes to slow the car down to turn in speed. as the discussion has provided, this can be done by better brake ducts, or better bias to the rear if possible. one thing that was fought on, was larger diameter rotors, which is the easiest fix in my opinion. greater surface area can dissipate more heat and provide 15-20% less pedal pressure for the same stopping force. yes, the KE is the same, but it will be less prone to grooving, and overheating due to the rotors better ability to shed heat going faster at the vanes and having proportionally more surface area.

as far as aero, interesting that your splitter is directing air to the wheels, usualy, it directs to the sides of the car , or splits the air to go into the engine bay, to be directed to the front hood area where there is a very low pressure zone that can be slightly relieved. the main thiing is that air is not going under the car, and thats where most of the downforce comes from . There is a lot of misconceptions there too, with splitters. guys , making coffee table splitters to be able to stand on them, when in actuality, if you dont want it to be crash resistant, it can be as simple as what i have. (not crash resistant in the least. . the most pressure it will ever see is .4psi at 160mph, and you can support that with a couple of wires as i did an a sheet of aluminum. Not pretty , but effective. interesting that the downforce of such a device, can be 500-1000lbs in the front!

Im not a huge fan of big downforce at laguna, due to most of the turns being so relatively slow and short. I remember doing a lap at thunderhill with the car with no aero at alll, and turned a time only a couple of seconds slower, on junk tires. if i was to guess, the aero , at the speed range im in, is worth 1 second at thunderhill and maybe .5 seconds at laguna. a much faster car with more power and speed, can probably see much greater gains, because the aero effects go up with the square of speed.

flatsics

Veloce Raptor

Some men, you just can't reach...

Matt Romanowski

I'm sorry that I replied to this thread thinking it might end up normal, not Kiborted.

Speedtoys

..it's almost as if I said not to forget to also update the REAR pads to work in conjunction with the new front pads to prevent this actual issue when I was asked for something new to try.

But..it's still my fault Mark ignored that advice.


I'm catching up, anyone ask him how he bed them in yet?

mark kibort

I asked a few that said that the pagid blacks were find as a match for the the fronts. if the bias is off, the subtle difference in pads i dont think may have have helped.

again, the bedding process was done correctly and did in no way abuse the pads. proof is in what the pads and rotors looked like when using them both in temp ranges they are designed to operate at.

Im really surprised to see that no one has produced one car that has run the 12.6" rotors. a testimonial would be handy right now. Im doing all that the posters have suggested before laguna. (ducting and bias change), but i still feel what im asking the rotors to do is too much.

333pg333

I get the heat thing and am sure it's not a hard fix following all the suggestions cited already.

The splitter doesn't deflect the air to the wheels expressly but more, away from the floorpan of the car. So in effect there will be more flow through and around the wheels adding cooling. As for allowing the splitter to be flexible and therefore collapsible as opposed to rigid and well, rigid...this is not how any pro team would design / build their aero systems. I can't see your splitter very clearly in your Avatar but a short flexible splitter isn't likely to be working to your best advantage. A larger, more efficient splitter will exert more pressure and therefore that's why people make them to stand on. (Earlier/smaller version of mine)

On my car when it was more like yours in terms of development we could go through a particularly fast 90o sweeper at about 105-110mph max...now with the car lighter, faster and way more developed Aero wise, we are seeing 130mph through the same turn. As you are heavier and less powerful you may not be able to push as much drag as we do with the dual plane wing but Aero will help your braking indirectly.

mark kibort

Matt, it might have, if i didnt get derailed try to explain why some dont understand some of the basic physics. And even if I was wrong about it, which i dont think i am, whats wrong with the discussion. Its all education, and cant hurt. Just look at the posts early on. Most of the time was discussing how the KE for a lighter car is near the same as a heavy car.
Truth is, it is. The reasons that some say that it wasnt, were incorrect, based on their descriptions and reasoning. (the 300hp for 9 seconds vs 10 seconds in the heavier car comes to mind in proof that the KE is different at terminal velocity) So, sue me for wanting to keep things accurate and correct in the discussion.
Sorry for trying to engage in a discussion and not just blindly say. oh, its cooling.... and be on my way.

For me, i actually have some good things to work on and experiment with.

I dont think cooling will help, due to my experiment on the track, and where the problem is occurring at the end of the braking zone, but I have the ducting and hardware on order.

I dont think that bias will help , because you willl always use the front brake to the limit of the tires, and the total potential of rear forces dont seem to add up to a level that can take more than a few 10s of feet out of the braking zone . thats not going to save the fronts . But, im goiing to double the bias range anyway.

I also have on order the heat paint to see where the temp problem is occuring and to what level.

I'm sorry that the sheep here have to just agree and cut checks blindly fo solve problems. some work and some dont. call me crazy for wanting to question and understand what I'm doing before i do it.

So, what could have been a discussion , turns out to be a stage where VR, Doug, Mike, KaiB, dumb dumb with his JPEGs, and others with nothing to add, can launch the put downs to make themselves feel superior. Its a very strange phenom. The funny thing is, ive seen these cowards in person on occasion. They are usually socially repressed, worms of people. They only get this brave on the INTERNET. so funny!

So, as i always do.. Ill take the high road. thought we could have a racing discussion among racers that know or have experience and i could exchange some ideas for my particular challenge and problems without this kind of juvenile behavior. Guess I was wrong.

Ill continue on here, because in my mind, ive just stated a problem. voiced some ideas on why im having he issue, and am taking in the suggestions.
many have not taken the road as others here, and have been very helpful and have engaged in the discussion like normal humans.

If you dont want to talk and discuss the problems. even prove why what i said earlier is wrong, then please dont pollute the discussion with insults, JPEGs, and misinformation.

If you do feel compeled to call names, chant insults, or other. I think you should look inside to what is driving this obnoxious behavior. From the words of the wise...... Grow the FxxK UP!

Mk

mark kibort

[QUOTE=flatsics;11509723][url="http://www.youtube.com/watch?v=ss/QUOTE]

Guys, look in the mirror for a second. You really think you are that good?
If so........ you know where to find me and see!
VR ----- oh god VR..... what are we going to do with you!!!!!!!

mark kibort

The reason i got into aero, is one, for obvious reasons. i have a lot of aero in my background, but really because when i got a real rear wing, i had a huge amount of push. so i started looking at some of the more progressive ways to get downforce, and came across the aero drawings for the 928 and ideas of hood venting, with splitters.
by the way, the splitter is not flexible and doesnt flex at 130mph,, but you cant stand on it. my point is that no matter how much downforce up front you get, the splitter is only going to have .4psi acting on it at 160mph. I have video of my experimenting with the splitter before i reallized what the min support needed to keep the splitter in tact, and not fold under the car. amazingly enough, you dont need a coffee table to support .4psi. a think sheet of aluminum will work if its level and you have support wires.
by the way, its a very effective splitter, thats over 6 " long it either has to work or it will deflect down... with the wires, it doesnt deflect down. Ill send you the u tube video proving this at 130mph. I even had a sunx sensor mounted to actually measure surface pressure on the splitter at different spots in and around the splitter. so, common misconception. splitters that produce 1000lbs of downforce, at 130mph have this much pressure on the surface itself. not even close!!
my splitter was 8" by 60" wide. Thats 480 square ". at 160mph, and .4psi, thats near 180lbs on the structure, but creating 1000lbs due to air flow redirection. i only see about 110lbs of actual force on the splitter structure at 130mph.

linzman

Your assumptions are wrong. I drove the car just as hard, if not harder after the weight loss. Although the 911 was a DE only car, I do have another car that I club race. I drove the 911 hard trying to chase my buddy in an SP3 car who holds several PCA track records in the NE. I assure you, I was not driving it any "easier", as you accuse. If anything, I drove it harder. Like at least 10 seconds a lap faster at the Glen. And the brakes lasted longer and never overheated. And since I didnt have ABS, it was pretty easy to know "the limits" of the brakes. So we've got significantly faster, driving harder, threshold braking (or at the limit as you say), and brakes stayed cooler. Maybe I used the brakes a little less because I was able to carry more speed in the corners with a lighter car, but I was also carrying more speed into the braking zone, so although I dont really want to calculate this out, I bet it was close to a wash.

If you truly lightened your car as much as you say, and now have more heat problems, something else is going on, like a dragging caliper, or the wrong brake pads that are chewing up the rotors. Listen to what people are telling you and stop digging in the heels about the KE. Do you want to fix the problem, or pontificate?

Anyway, although this thread started out interesting and funny, I too am now done.

RickBetterley

Funny, almost every time I try to load this thread, Rennlist times out.

Matt Romanowski

People have tried to help, but you refuse to pay attention to pretty universal things and then argue absurd things. You have to do the basics first - add cooling and get the bias right. Reducing the weight of the car will decrease the requirements put on the brakes. By your logic, the same brakes that work on a motorcycle should work on a freight train because weight doesn't matter.

Good luck, I'm done.