mark kibort

Here is another quote from some published racing sources:

According to "Analysis Techniques for Data Acquisition" (published by SAE, author works for/manages FIA GT and LeMan teams), a well driven/well set up car is typically capable of cornering at 103-105% of max braking g.

By the way, If Im running ABS, which I often am not, I dont engage it.

So, is this still a mystery now?

Im still looking for the actual reasons, again, I suspect it has to do with the contact patch orientation and tread deformation, slip angles (%) etc.

mk

GregBBRD

Yeah, I'm going to suspect that this is for a FIA car with uber trick slicks and a uber trick chassis that allows for almost no roll...not a 928 with dumpster tires and one tire completely off the ground, in corners.

I also think you will find that FIA cars don't allow ABS.

BTW...you are leaving 2-3 seconds a lap, on the table, by not using your ABS...you should be using it in every single corner. The use of ASB and a decent limited slip allows insane trail braking.

It is possible, in today's "internet world" of people writing volumes of unproven bull****, to find some quote that will justify almost any statement anyone can make.

So, yes, it is still a mystery.

gb

entropy_engineering

I have a quick question (which I guess has little to do with this post). I have a found a few vehicles I drive that with practice I could brake harder without the ABS. I understand that braking should be on the edge consistantly. I believe the the rate of modulation in some ABS systems is too "course" to let optimal braking. In other words, I've done some back to back experimenting, particularly in the rain, and found that I could beat the ABS system. Is that not normal? I suppose a well thought out system would reverse the results...

mark kibort

Ill have to call you on that one Greg. You must not have ever driven a 928 in anger with and without its stock ABS system.

Threshold braking is threshold braking. a skilled foot can out brake "Most" ABS systems. Now, if you are talking about new supercup racing ABS, the only difference there is going to be the saftey net in a panic stop.

Having run our ABS systems in a racing situation, I can tell you first hand, that it is ONLY a safety warning system, NOT even a safety net. when ABS starts to engage , it helps with threshlold braking, but IN NO WAY , can increase your lap time performance. When 928 ABS engages, the dwell time is so great, that it will growl at you while you skate down the track at near 2X the stopping distance. However, on ICE, It would be close. (and Ive driven the car in the snow to test that as well )

Now, back to G loading, it doesnt matter if it its slicks or DOTs, the tires will perform proportionaly. I have the G read out from the Iphone, plus a lot of other car data from our class in similar speed cars. Cornering is usually always higher than braking g loading. Probably having to do with the tire's shape and deformation in each instance. If you look at how a tire deforms during a stop vs a turn, it becomes pretty clear on why turning g's are more than stopping.
The only reason its the opposite with formula cars, is that they can have downforce to equalize the forces, and counteract weight transfer to make more use of all 4 stopping tires. Roll stiffness or amount, helps with cornering Gs by effectively lowering the center of gravity. You still have weight transfer. So, by lowering of the center of gravity when you reduce the roll for cornering, you increase g loading capability. braking and cornering weight transfer only depend on g loading, width or length and CG.

So, a dose of reality here. I'm leaving 3 seconds a lap with not using ABS?
So, I'm running 1:37 at laguna with 373rwhp, and anderson did 1:40.1 when he had 420rwhp back in the day. AND, Im now going to improve that to 1:34 with ABS? (the winning time of the 2003 Speed GT WC laguna event with Auberlin, Said, Stuck and Mumford winning at 1:34.xx.?? By the way, I use ABS when the relay is working, but if it isnt, it doesnt do ANYTHING to my lap times at all.

So, I get my car around the track with a lot of trail braking as it is. Times do speak for themselves, but the video speaks even louder. I think Anderson has removed his ABS system as well, and I think if you ask him there is not 3 seconds lurking if he put it back in. That certainly would have been easier than the CF intake that got him the 3 seconds with 80 more HP! (i.e. laguna went from 1:31 best from 1:34 with the new intake.)

mk

GregBBRD

I'm pretty sure that the pictured modifications to the oil passages are actually going to hurt things...not help.

Let me carefully reword that...that pictured cradle/block are junk.

Porsche put those restrictions and reduced the size of the oil passages for good reasons...they don't look like they do, by accident.

Oil back fills passages. All fluids back fill passages. Simple fluid dynamics.

Fluids flow to the farthest point, hit the restriction, establish pressure, and then slowly begin "back filling" from there. If you want to see this in action, buy a "soaker" hose at Home Depot (if they still make them)...one of those hoses with a zillion little holes in it. Hook it up and turn on the water. The waterflows to the end and water starts coming out the holes closest to the end, first. Eventually, the water will start coming out the holes closest to the spicot, but not until all the other holes begin spraying...starting from the far end, first.

So, those restrictions and steps are designed to allow oil to back fill the cradle quickly and get oil quickly to the bearings that are closest to the oil pump. Removing the restrictions ruined that ability. Now all the oil is going to flow to the rear main and off to the heads...since the rear restrictions have been removed...and the passages that fill last are going to get pressure even later.

You're going to have hydraulic lifters happily bathing in fresh oil...before #2 and #6 even get a hint of oil pressure. That's a bad thing.

mark kibort

There is ABS and there is ABS!! old ABS from 1986 is not really that effective. a skilled foot can SLAUGHTER stopping times of our ABS system. When you get into modern day racing brakes, its probably equal to a skilled foot. (more than a good probablilty) This is proved all the time with SpeedGT cars as some are allowed ABS and some are not, and some can have it with added weight as an equalizer for same car class rules. The difference of braking with good drivers is non existant. If Mark A was to lose his ABS on his porsche GT3 cup car, he would turn the same lap times, BUT if he got into touble, he might flat spot a tire before he was able to correct. (only in a problem situation) normally, threshold braking of a good driver will always exceed ABS.

If ANYONE doubts me. Ill go out and find a stretch of road and put video on the car and do a comparison. 120mph from some marker and see which can stop faster. Having engaged ABS at the track on ocassion, i can tell you that it is like being on ice skates when it engages. same as my bmw street car too.

mk

mark kibort

That doesnt sound good! Sounds like a key principle was missed here in the modification goals.

Guys, has this ever been done on a 928 engine before???

mk

entropy_engineering

I feel that space permitting, the oil passages everywhere should be garden hose size with the only restrictions being the individual units using the oil (bearings). The only exception here to me would be the heads, which frequently do or should have a flow reducing orifice in the top of the block. I've built a handful of pretty serious Mitsubishi 4G63 engines (the turbo 4 banger) in the range of 500hp. In my builds that level I REMOVE the oil squirters in the block. Forged pistons with ceramic coating don't need the oil cooling and it leaves more oil for the crank. Common practice for those.

entropy_engineering

In my last post I meant I would never want to intentionally reduce flow to any part of the bottom end. The only flow control of oil volume should be the rate of consumption by the bearings themselves.

Lizard928

starting with the ABS comment by Greg,
I am afraid that you have ZERO clue what you are talking about here! The stock ABS system on the 928 right upto the 1990 model (latest I have driven) is great for ice, it is USELESS compaired to a trained foot on the track. If we were to take two equal 1987 cars, same wieght, tires, brakes etc. and go out onto a track, and you were to engage ABS on every corner, and I was to simply use my foot with it disabled. I could 100% guarentee that I would post significantly faster laps than you.
The stock ABS system is jerky, clunky and overall not that great. On the track smoothness is key. If you use ABS to trailbrake in one of these cars, it is likely that you will spin. Esp with a higher rear bias valve which can dramatically cut down your braking distances.
I do agree obviously with what Kibort has written above, and I could do the same test, with disabling the ABS in my own 87 and could achieve the same results and reduced stopping distance without the use of the factory ABS.
As well I have talked at length about ABS with people who work in the field of testing and designing the systems, and they claim that once heavy modifications are done to a car (ie severe lightening) it is actually a better idea to completely remove the system as it will be working outside its normal operating range.

As to my block/girdle modifications, yes it WILL take a tiny bit more time to fill up the extra volume with oil at startup. How much time though, we will be talking in the millisecond range. Your analagy with the watering hose is missing one large piece, in that if you were to remove pressure and the water had the ability to retain nearly full water (which is how the engine works, as the oil does not all flow back into the pan), and then you were to turn the water back on the flow would be much much more linear out of the hose. As well the hoses are normally 50+ feet, and have lots of volume. The volume that we have in our engines is so small, it takes milliseconds to bring up to pressure.
As well Louie has done conclusive tests which show that there is not excessive flow to the heads. This is because of the tolerances and clearances that the factory has. As well I have not increased, or removed any real flow to the heads. Mearly decreased the restrictions to the mains which knowing fluid dynamics is NOT a bad thing.
You say that you get more oil to the mains by running greater tolerances, what about getting greater oil to the mains by removing restrictions instead?
I also do disagree with your idea as to why they had restrictions there in the first place.

One thing that I find funny is that everyone seems to think that Porsche did everything for a reason. This is sometimes the case, and sometimes the reason isnt for the better! Look at the Boxster, Cayman, or more in this cars timeline, the 924, 944, etc. There is undisputable proof that Porsche restricted the performance of the 924/931 esp so that it would not compete with the holy 911. As well what about the fact that the 928 was supposed to start life at 5.0L and because of the oil crisis it got lowered to 4.5L?
How about the horrid camshafts in the S4+ cars.
There is tons of things that Porsche has done to lower the output of certain cars to keep another one of their cars abit faster. As well technology and understanding have advanced a GREAT deal since 1976.
And we all have to understand that the people at Porsche designing these cars are just that, people. We all have limitations and different ideas. There are a million different ways to do a million different things. Some are better than others, but if the people designing something dont think of it and just come up with a solution that "will work" and they dont have anymore time to spend designing it. Then it gets left at that and probably never touched again.

And Mark,
As to my girdle mods, I do believe that very similar, if not the same mods have been done by a few people over the pond with good success. But I was not able to get full details on exactly what was done by them. The info I had was that the passages were restrictive and of poor design and they had measurements for each of the oil passages, both depth and width. They claimed that they opened up all of them, but that was all I could get. After doing my own studying on the girdle, I had these mods done based on my own knowledge.
I will however let you all know if I bolt it all together and I notice any issues with it either right away or after the first season.

Lizard928

Agreed 100%!

entropy_engineering

Hey Lizard931 (I bet that's not your name huh), if you still have any bearing wear issues I have a thought. The drilled crank, dry sump, etc. are all good in my .02 as well as what you've done. If that's still not enough I have an odd but simple plan you may have seen in an old post of mine. First, I must admit to having a wine and caviar diet on a balogna and beer budget, but I have plans of a healthy turbo car myself one day hopefully this summer. Not 100% sure yet what I will do about knock sensors, but I plan to have the back of my main bearing webbs drilled vertically thru to make a hole in line with the three plugs (or atleast one above the #2 main) in the top of the block. I'll have the hole stepped a bit larger on the top side so I can make a screw in fitting with a tube that will fit tight in the top of the main bearing web. Then I can use a braided line(s) to externally route oil from the oil filter area into the top of the block. Priority main oiling baby. Perhaps that may help you in your quest sometime. I think the maching would be dirt cheap. Making the screw in fittings with AN adapters shouldn't be too hard either. If I weren't worried about trashing a block from going off center, I think I could set up a block, indicate it in, and drill myself on a big drill press. I realize the stock intake won't fit unless it's REAL low profile, but the stock intake isn't part of my agenda. So why did Porsche put those three holes up there in the first place over the mains? Hummm.

mark kibort

I would take it a step further. I guarantee you would miss every turn in point and overshoot every turn. (if you mashed on the brake with ABS at the number 2 marker at speed at any track turn in ). Worse yet, it is hurkey jerky and could cause all sorts of other instability for a turn in.

The main thing that i use it for now, is for strictly a safety net. When at laguna, there is a trememdous threshold braking point approaching the corkscrew for example. Without abs, there are times where you can get the inside wheel of the approach turn to get light an lock up. It happens so fast that sometimes its tough to release and re-apply brakes to make the turn-in and not lose time. With ABS, it becomes an early warning system that gives your foot feel that something is not right and allows you to modulate earlier.
There is no drawback for keeping it installed and operational. (except for the added weight) However in tests to see if its working, its amazing how far the car will skate forward, well past a skilled foot application of brakes.

Scot has no ABS to fall back on. he does a pretty good job of braking, running a 1:41.xx at laguna. occasionally, he will do what I mention above and it slightly flat spots a front tire. This will never happen with the ABS. thats what it is good for.

mk

GregBBRD

I would submit that you are not using the ABS to its capacity. This is very common.

BTW...this applies to Mark's response below, also. He has the same problem, obviously.

There is simply no possible way for your brain and your foot to "beat" ABS...ABSOLUTELY NO WAY. The naive statement that you can is....uninformed. You can not sense which individual tire is locking up and then modulate that tire, while increasing (this is the big clue) the braking on the other tires that are not locking! No way, no how. Even if your brain and body could do it, there is no way to have the brake fluid do it!

The biggest problem drivers have with ABS is that they don't understand it or use it to help them. Good drivers do understand this and they do use it fully to their advantage. The new 997 Cup Cars are faster, in every way than the 996 Cup Cars. They have significantly more power, better gearing, far better handling, better differentials, and are 2-3 seconds faster on any track...by themselves (professional drivers here, not club drivers.) Mix in 996 cars, with ABS (also with pros), on any track where the horsepower advantage of the 997 cars is not enough to pass the 996 cars, and the 996 car will always be in the lead! Why? The 997's can't get by and then keep the lead, under braking. The 996's can outbrake the 997's in every corner...and then be "in the way" of the 997's everywhere else. The significant better performance of the 997 is outweighed by the better braking of the 996!

I've been fortunate enough to be involved with Porsche racing and performacnce for over 40 years. I've driven almost everything they have ever made. I've been fortunate enough to ride in cars with very good drivers and I'm smart enough to know that I'm not one of these. I've been on race teams and watched. I've ran race teams, I've had good drivers. I've had bad drivers. I've had drivers that beat the crap out of cars and go slow. I've had drivers that knew how make cars go very fast and not kill them. I get it.

ABS requires an entire different style of driving...if you use it wrong...it doesn't help..you are correct.

Here's some clues:

When you feel ABS...do not "let" up....the lesser drivers do, the good ones do not. PUSH HARDER! Get the entire car into ABS...Make the system do its work. The car will absolutely suck itself down and toss you into the harnesses harder than you can imagine. Yes, you will be slower, in lap times, at first. You will be braking and slowing way more than you need to. You then need to learn to drive the car deeper and brake later. You need to "trail brake" (actually be braking the car while going through the corner.) A good limited slip is manditory for this. A "trailing throttle locking differential" helps significantly. Once you figure this out...the car will be 2-3 seconds a lap, faster.

At one time, I didn't get this. I didn't use ABS either. I was fortunate enough to ride, in my own car, with Walt Moss...certainly one of the most gifted Porsche drivers I've ever sat with. He was an instructor at Bondurant. I had a 964 bullet. This was about 1994.

There was a corner, down at the far end, that made a 180 degree turn and returned you back towards the main race track. There was a chain link fence about 40 feet off the edge of the track and beyond that a city street. I had been driving that corner, with Walt riding, for many laps. I did non-ABS braking in a straight line, before the corner, turned this rocket the opposite direction and went the other way...faster than any human being could do it....No doubt about it! Then Walt asked if he could try it.

Now, Walt had never driven a Porsche with ABS...this was his first, ever. We drove around this race course, a few laps, while Walt settled in an got used to the car....I began to feel the "shudder" of ABS. He "got" it. Then all hell broke loose. Walt went down into that corner, with his foot planted in the accelerator, and never even thought about the brakes, until I was absolutely convinced that we were going through that fricking fence. He then stuffed the car into ABS, turned that fricking corner, while under braking, got that stupid car somehow pointed in the opposite direction, and stuffed the throttle down.

All I could do is laugh. And feel humbled. And ask to get out of the car. And change my underwear. And think about what the hell I could do in racing...driving was never going to be it!

I began to use ABS. I was consistantly slower, at every race track, than I was without it....I was slowing the car down too much. I had to re-train myself. It took time.

Go out and try your ABS. Try it on your street car. When you feel the "pulse" of the pedal, don't let up...push down as hard as you can. You'll get it.

You guys that think you can drive faster without ABS, on a race course, than with it...you might think about finding another hobby, if you can't change.

It's still a mystery, but I'm starting to get it! A car touching the ground, going through a corner, with three tires might pull more G's than one with 4 tires being braked...if you aren't using the brakes. The "dream-o-meter" instrument used to measure these forces just needs to calibrated for reality....another common problem.

GregBBRD

Colin:

I frequently have "ZERO clue about what I'm talking about". My big thing, in life, is to just hear myself talk. Everyone that has been around me knows that.

Seriously....I'm not here to conflict with others....I'm just trying to share what I know and what I've done.

However, I'm going to "throw out" a little thought for you, that you might want to think about, when you say "you have ZERO clue what you are talking about here"...I've probably built more Porsche race engines than everyone else, on this 928 forum combined, has built Porsche engines. I'd also guess that I've ran more race teams than everyone else here combined. I'm also going to guess that I've "coached" more drivers than everyone else here combined. Just something to think about.

Pretty good, for "ZERO clue"! I'm happy. "Faking my way through it, everyday"...that's my new motto!

You can do whatever you want. I'm just a simple "clueless" mechanic that happens to build an engine or two, every once in a while. My opinion is just that...an opinion. We don't need to argue about it, or get excited about it...no big deal. It's just an opinion...with a little bit of experience thrown in. I do modify the oil galleys, but primarily to direct more oil to the #3 main bearing, when the crank is modified for additional oiling for the rods. These modification are, as of right now, proprietary. I wouldn't want anyone to mistake my "ZERO clue" ideas with obviously great ideas.

If you think Porsche stuck that giant restriction back by the 4th main bearing and then shrunk down the following oil galley, because they don't know what they were doing...have at it...like you did. What the hell do they know? I'm sure they did that purely by accident. Hell, I think everyone here should do the same thing. I'll pass, of course. Thank you very much. I'll hold my own cards....even though, I clearly have..."ZERO clue".

You sent me a PM about helping you with oiling ideas...sounds like you've solved it on your own and
don't really need or want to hear other ideas. I, frankly, also don't feel the immediate need to help someone that says "you have ZERO clue about what you are talking about here".

Nothing personal meant by this...I just have better ways to spend my time.

I hope it works good, for you...honestly.

regards,

ZERO clue.

My "new" signature! Thanks so much!