I remember that sequence of pics from the past Jack. Sorry to say but they are quite memorable and I love that close up. So much going on.

Mike,

Thanks for taking the time to respond in detail. I guess I'll address each numeric point.

1) Don't know the tyres that well. Have only limited experience driving them and slicks on the whole. In general haven't had issues in the past when on them though. There does seem to be some conjecture over them in some circles...the Hoos I mean.
Have never had to scrub a huge amount in my car (mostly on RSpecs) and my friend who drives a similar cars on similar slicks doesn't scrub in at all...but it's not to say that you don't have a very solid point.

2)Assuming you mean to have brake and wot lights visible on film for analysis later? I will have a better setup with data overlay soon enough. Or do you mean as reference while driving?

3)No, basically you're pretty correct in that assumption. Although the track layout as shown is either pretty fast or very slow corners. Not much inbetween. T3 is probably the one where I could have loaded up the tyres more. (T1 being the crash turn for reference). What you see is me pretty much pootling around the track trying to get a feel for the new car. Having said this, the track is actually more a momentum track that you need to string corners together. Well the full track is in any case.

4)It's an OMP seat similar to a Recaro or Sparco. I have my eye on either a new Cobra or RaceTech seat and will have Hans and net as well.

5)Again, probably right. Although funnily enough I would have liked to have taken an earlier apex at T1 as there is a bit of a groove through there, but yes, I have to agree that some of the turn in points were too early. I have a bit of a gut feeling that if you are really on song, an early apex in some cases is the fastest way around some corners...but I wasn't on song or particularly confident with the car being a bit twitchy in general. The tail had stepped out previously and it had picked up a wheel at T2 which we thought might have been the LSD at one stage.
The car is at the upper end of most 951 builds but not sorted. There is still a large rear wing to go on and I'd like to do some underbody aero work.

You can read about the build on this thread. Please ignore the rubbish that killed it off! http://forums.pelicanparts.com/suppo...eys/behead.gif

http://forums.pelicanparts.com/porsche-autocross-track-racing/661835-my-build-what-its-worth.html

6)I'm getting the general impression that I was pretty much toast once off the track. Even though there is video of the whole thing, in my mind it still appears like a slow motion 'click-click-click' photo sequence and so I don't realise how much speed I was carrying when thinking about possible alternative strategies.

Interested to hear your take on the 911 vs 951 theory? The 944/51 is an easy car to drive pretty quickly but I think to really push it you start to slim down the window of forgiveness. Whereas the 911 is a known quantity and most will probably follow the 'slow in fast out' theory and do pretty well with that. The way they get out of slow to medium corners is unparalleled but the 951 is faster through high speed sweepers and I find under brakes too.

+1 on the Racetech. That's what I just put in. It's a bit odd, as the seat really hugs you right up to the armpits and with the halo, it's a bit tough to look around hairpins, but one thing is for sure....

I ain't goin' anywhere.

Patrick, why are you giving Winder a lead-in like that! The 951 is well balanced and is a very stable platform. However, at certain unfortunate trajectories, our cars have more in common with a spinning top!

Of course as you know, it is hard to tell anything from a video.... but here are some additional thoughts...

1. As you likely know, all tires have an optimal temperature, pressure and slip angle for max grip. The former two are in a range.

I have about 25 years of track driving experience, 10 of those on DOT sticky tires and 10 on full slicks. What I have learned from expert friends and my own experience are some techniques for getting the slicks up toward temp and pressure range. These techniques are different from what I did with DOTS. I think the DOTS get where they need to be faster from normal driving than do full slicks. On slicks, one of the benefits of the process is that I get some feedback as to where I am in the process before I start pushing.

2. What I mean is to have some type of light in the dashboard that is setup to come on with the brake lights. It doesn't have to be huge, just big and bright enough so that you can see it in the video frame with your hands and the full view between windshield a pillars. There are several threads with examples on these boards. I use a small red incandescent light for this. I also have a green incandescent light that comes on when the throttle is pinned wide open. So when I watch the video, I have a clear indication as to when I brake, trail brake and achieve WOT. You can consider this "poorman's data acq.," I consider it enough. With this approach you will have these markers in the video before you do any fancy editing or synching with data, so it is always there for reference if you do not have time to monkey around with all of the other stuff.

3. It looks to me like you were going very easy, which may have lead to a "less known" state of grip in the tyres as you may have not had much feedback on what was available. Then you get into a situation where you think you have plenty of slip for acceleration since you haven't used it all up on cornering... but you are not calibrated as well as you could be, or you get an infusion of BHP from a certain place in the non-linear boost curve.

Again, boost onset must be learned. It is an additional input variable for the driver to deal with that must be managed. There is a reason why Hank Watts says to start with late apexes in a turbo car...make sure you are pointed where you want to go at boost spike.

In my opinion, there are no such things as momentum tracks or cars. We want to go as fast as possible for the minimum lap times, so we want to slow down as little and as infrequently as possible, using all the car has to offer. No getting around that.

5. see next post

5. There is a lot of confusion about the term apex. I try to stick with the definition that involves the widest possible geometric arc, which is always our starting point. Call this geometric apex. If we go earlier, we cannot make the corner, and if we go later, we leave cornering speed on the table.

Now, the actual desired apexes we try to drive often deviate from the engineering drawings of the track. Our cars are not perfect objects of physics and trade-offs are involved. Let's call these desired apexes. Once we know what they are for our car and our circumstances, we try to be within angstroms each and every lap. Not inches, and not feet, not centimeters.

The concept that "earlier apexes can be faster" is rubbish in my opinion. If we achieve higher cornering speed by intersecting the inside of the track earlier, then we made better decisions about the trade-offs. Were were able to achieve this with higher cornering speeds and stayed on the track... great! We made a better set of choices! No confirm and repeat!

I advocate choosing "obviously late" apexes as we learn a new car and/or track. Gives us room to adjust at the exits if we make inappropriate decisions about entry and/or cornering speed, and helps with boost issues.

Sounds like you may have also been getting used to behavior of a different LSD as well. Another variable to learn.

Remember, I know a fair amount about 951 builds... having had several of those cars and being a part of that world for many years. I consulted with some serious pro racers about these cars back in the day, and there haven't been any great revelations since then. Sounds like you are set up for quite a bit of boost. That was never my cup of tea ($$$$).

6. If you had a brake light in the camera FOV I could get a better feel for the timing of brake application going into the corner and once the accident was eminent. I am not sure what you could have done with all of that wet grass,but it looks to me like you did not slow down at all. I assume your foot was planted down on the brake pedal. An unfortunate occurrence at a bad place on the track. Again, maybe it was a set up thing, but I think more likely limits were exceeded in a situation where you weren't pushing and considered yourself well in bounds.

As for 944/951 versus 911 handling, there are lots of ways to compare and contrast. Neither car is inherently faster than the other. Nor brakes better. Depends on the specifics of the car. It is my belief that you drive a car for what it is, and deliver inputs based on feedback and knowledge of what the car is

In my experience, slow in fast out has nothing to do with it. I use that term to discuss trade offs with students... that is what good does it do to lose less speed on entry (brake later or softer or whatever... "faster in") if we get to WOT much later than a "slower entry" approach? I usually say, "when in doubt, slow in fast out."

Again, I hope you mend rapidly and without much discomfort and hassle. When you do get your wheels back together, it might be a great idea to augment on track sorting with some skidpad and/or AX work.

In the engineer's report he says you were going 16km/h faster on that lap at that corner than your previous laps. This tells me that you need to be more gradual in your learning to drive the car fast. It takes alot of track time to get consistant and to develop car control. Just take a more gradual approach to getting faster. The best way to learn car control is to push hard in the slow corners first so you can get used to sliding and catching the car. Then work on the medium corners and finally the fast corners. Until you can enter a turn within 2 or 3 km/hr consistantly you can't push hard in the fast corners.

Once you left the track, there was nothing you could have done differently. Before you left the track the only thing to do was better corrections so as to leave the track pointing straight ahead. This ability will come with more practice at the limit (starting in slower corners).

-Andy

Andy, on face value I can see what you're saying but I have driven that track plenty of times before at similar speeds in the same car (before it was changed). The 16kmh increase was more reflective of the slower previous lap where I was often held up by the car in front more than a sudden ballistic jump in speed. However I'm sure there I'll be a little more careful if I get this repaired and back out there.

Mike, a lot to answer and frankly I'm just a bit too beat to get into it right now, but I do respect your input and am thankful for it. I agree with much of what you've written although would like to continue to discuss one or two facets.

My feeling is that there wasn't 1 single cause for the crash but more likely a combination of 2 or more of these things. Not discounting driver rustiness either.

1) Cold tyres
2) Lack of aero balance
3) Suspension issue. Lack of droop &/or too stiff rear springs
4) Fluid on track
5) Bump in surface
6) Component failure or installation issue

Rough crash man, thats a shame! Just try and stay positive, crashes happen period, best drivers in the world crash, its a risk that comes with what we love to do! I got two Saabs in the junkyard from rally, nothing you can do sometimes

Hope you get back to the track soon!

No sweat.

It is hard to have a conversation on the internet.

It might be helpful to describe and then discuss these things in three basic areas:

The car's changes from what you were used to at this track. For example did you go from a~300 bhp and 3000 pound street/track car on DOT tires to this current car? Since experienced drivers are used to things like changing conditions, and since set-up issues often manifest in several places around a track, many comments and suggestions here have focused on the concept of learning the limits of a new car.

Untoward track conditions. We know the off track conditions were untoward, which really, really sucks. But what about bumps and/or fluids on the track? Did any of your previous forays through that area lead you to believe that something like that was going on?

Problems with car. Set up issues that lead to step function changes like a sudden infinite spring rate or a broken part.

As an aside, I remember back when I installed a Lindsey boost enhancer in my 951. I thought it would be a cheap way to have variable boost, though not cockpit adjustable. I had custom Milledge chips, a shimmed stock wastegate and a drilled factory cycling valve. I installed the new part and adjusted it in street driving to just a tad over the previous boost level, whatever it was-- probably just beyond stock. My idea was that I could turn the boost up a tad bit for timed runs on Sunday.

Well, the car was scary loose on Saturday. Boost onset induced oversteer in several key places around the track. I couldn't do the same lap times as previously because the car was so loose. My co-driver/wife noticed it too. Instantly. She was pissed! So off it came for Sunday. We changed the shape of the curve with that doo dad, and it changed the way the car drove. Turbocharged cars have that extra variable. I sold the gadget to someone with a street-only application. Later I found a pretty much brand new Tial WG on a wreck at Partsheaven. Bought it for $100 (they were as I recall $400 retail at the time) and installed a proper dial a boost set up in the car.

My wife still tells the story of the scary loose car at dinner parties..."my husband is always changing the car..."

Mike, I'm still not sure if you saw the build spec ( http://forums.pelicanparts.com/porsche-autocross-track-racing/661835-my-build-what-its-worth.html ) but this wasn't just a shimmed wastegate upgrade type thing. However the car before was approx 3000lbs with approx 350bhp. Now it's 2600lbs with approx 430bhp. I say approx because the dynos we use are very conservative and it was hp to the wheels. So to get hp to the crank is a matter of debate. I think the factory actually multiplies by 1.32. So we had 360whp which would be more like 385whp on many other dynos. In fact he actually did another pull to show how by merely adjusting the ramp rates and positioning of the car on the rollers could give an immediate increase of 25whp.

So anyway, yes the car has a pretty good power to weight ratio no matter which way you figure it. However it felt generally pretty progressive and not really laggy, laggy, laggy...BANG!!! Also as you can see I am going through a constant radius corner and am virtually floating around there. Again, the Engineer said that I introduced 20% throttle earlier than the previous lap, but I don't think the previous laps are really a good control figure to compare with.

I am hoping we find something that either stands out like dog's bollocks or at least gives us cause to nod and tut tut.
Oh, and yes, there was enough symptoms of irregularity in the setup on previous laps that day. My feeling is that we will turn the boost down next time out and get a more progressive re introduction to the new car.


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Just out of curiosity what made you decide to go with a 900/ 1100 setup for your car? That is def a stiffly sprung car, esp for a car with minimal to no aero

Watching the vid to me that track seems pretty rough, as you track in I noticed your fighting what appears to be the tail starting to step out over some rough parts of your track in, then its kinda hard to tell but it seems like theres a slight crest you rise over as your rear end finally gives out. Stiff springs would def. cause a scenario like this, as your tires start to bounce over these bumps and lose contact with the asphalt your gonna slide, the fact that a 900/ 1100 setup is biased towards a bit of oversteer anyways is gonna make the problemo worse, and if there was a slight crest there like it looks like coming up over that just released the whole monster at once.

Just my .02 cents I would have your engineer look into what natural feq. your running with those springs, IMO 2.5 cycles per second is getting a lil too stiff for a car with no aero, but if your at 3 or over it could def have played a big part

Anyways I hope you get some help from someone on this board, also if you've switch out the tb's for a coilover system I would step down the spring rate

I read parts of that thread. I think you may misunderstand what I am trying to convey about boost. Perhaps we can discuss that further, later.

It is difficult for me to speculate on spring rates since so many variables are involved. I think of the car as a system, and usually seek out professional basic advice from people with experience with my type of car. When I had my 951, I was lucky enough to get some great input (and parts) from Kelly Moss and Jon Milledge. Others as well, plus we had a lot of guys running similar cars so we compared notes. The tracks make a difference as well of course.

Your car would be categorized as a GT car in many forms of club racing here. It is heavy for a GT car. We see a lot of 1900-2300 pound 911s in our area, and they run rates from the 500s to likely near 1K as set up by knowledgeable folks. My car is toward to lower ends of those numbers. To me, a 2600 pound car with the rates you describe could make sense... depends on the types of input one has from others, and so on.

All I can do is basically guess, based on my experience, the video and what you have described. I doubt aero or basic set up would trip up an experienced driver like yourself. Perhaps a new pavement bump with which you were unfamiliar. Perhaps oil or anifreeze-- we always need to watch for that.

To me, unless something broke, it may just be that you exceeded the limits with your right foot, and your opportunity to correct the error was non-existent. And unfortunately the inherent speed in this corner and the off track conditions made the penalty high. Of course these kinds of things happen...

I remember one of my fellow racers with a factory GT3 Cup crashed at 10 at Sears a few years ago. He had a lot of experience and skill, and was level-headed guy. We had gone through there with inches between us many, many times, and I fully trusted him. Then one Friday test day, some guy we didn't know crashes his Cup in 10 and winds up upside down near pit in. Unhurt, but car is totaled. A few hours later, my friend crashes his Cup car into the turn 10 tire barrier and cracks a couple of ribs. Car is totaled. He had just taken out insurance, so he was covered. I have not raced against him since then. They never figured out what caused the crash, but there was speculation that something broke.

Turn 10 is a place where if something goes wrong you can get damage and injury, even if you were only going 5/10s.

Wait a minute.... "hoop spoiler"? Like from a 968?

No rear wing?

Is that correct?

That could be a ginormous ah ha.

Add a large front splitter into the equation....recipe for snap oversteer!! The faster you go the worse it gets.....

Scott

The Motons inc springs were supplied by them in what I was told is their 'kit' for race 951s...but this may have been for their smoother tracks in Europe too. Also, there is a significantly large dual element rear wing to go on the car which we just didn't have time to mount. See pic.
I do think it was more than one issue that caused me to crash but spring rates are certainly being looked into.

I'm sure the spring rates can be applied to this car, but perhaps with some changes...such as going from a hoop spoiler to a proper wing! I'd be happy to discuss boost with you as I'm not quite sure in which way you're referencing it? While I have a bit of experience, I'm no pro. I suspect a bit of rust also contributed to my demise. I'm man enough to hold up my hand on this one. Sounds like there could have been fluid on T10 that day?

While the front splitter isn't huge, I tend to agree that this has added to the mix. Bit of naivete on my part on top of over enthusiasm of getting back on the horse from a long spell.

http://forums.pelicanparts.com/uploa...1336119071.jpg

Yeah I'd just have your engineer look into what natural frequency those spring rates are giving you! Also I would def suggest getting some track time in an aero car, what a huge difference it is driving a car with significant aero. I remember a few years ago I did the 4 day race course with Bob Bondurant out in AZ and moving into those formula Mazda's just wow, thats all I could say. Its a completely different ball game thats for sure!

Interestingly...or more confusingly, I've just been re-reading a paper prepared by a suspension analysis expert who went over another 951 (which also has all Racers Edge aftermarket components and Moton Clubsports) and who had 800lb springs all round, and his suggestion was to move the rear spring rates up to at least 1200lbs. This car has no added aero nor even a front splitter. He nominated a number of other modifications to be done to help with roll center, bump steer, scrub radius, force application point etc.... The frequency ratings are 3.25hz (f) & 2.34hz (r) with 800lb all round. By moving the rears up to 1400lb which he also didn't rule out, the rear ratings would come up to 3.10hz.

So it's interesting what different viewpoints you can get. The guy spent a full day in the workshop doing all the measurements on this car so it wasn't a cursory glance and pulling figures out of the sky type thing. I'm not saying I'm going to do the same thing btw. Quite possibly the opposite yet this suspension guy would think I'm crazy based on his recommendations.

Before and after shots...http://forums.pelicanparts.com/uploa...1336191967.jpg


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