KenRudd

On the rack now..

mark kibort

Carl, my aliment is not pinned in the rear.. im not from the school of pinning the rear end. all i saw from other cars that have pinned was them being way way too loose. Anderson and i discussed this many times and seemed to agree, but he had no way of "unpinning" his, due to the after market geometry he installed.

i mentioned roll cage and softer suspenstion settings which are critical to alignment setings (like tires as well)
the more body roll, generally the more camber you will need, but the more it will wear the inside of the tire, as well as compromising grip . generally, as it turns out with all the trade offs and the generous amount of camber compression gives the 928, 2 degrees seems to be optimal for street and racing. maybe 1.8 or so for street / track duty

this happens to me all the time after my races! the only thin the 928 doesnt do as well as the lighter 911s is brake , but thats a weight/ and sometimes a driver thing.

FredR

Carl,

The thing I did not mention was that on the next lap I then went to the back of the field and decided to hoon around a bit. Given no overtaking was the remit I let the rest of the field go and then played catch up. Fortunately we were only using half of the back straight from a standing start rather than a flying entry. The Porsche team put out markers to show the breaking point, & the turn in point [it was a factory DE event] but even so I went past the breaking point at around 100 mph, left my braking effort very late to test the trail breaking ability, hit the brake pedal about 50m before the turn in point and crap- no brakes- the fluid had boiled. Worse still the track was new, the run off areas were not grassed and they told us not to go sideways into the sand if anything went wrong as we would like roll over.

In a split second I told my passenger to hang on as we entered this right hander 180 degree turn and threw the car into a spin with the auto box lodged in third. I left a huge darkie on the track [first time used] and by now was doing about 60 mph mostly sideways and scrubbing speed rapidly, figured I could get round the bend by going back on the throttle, the resulting wheel spin arrested the forward component and my rear wheels just plopped off the edge of the tarmac and immediately buried themselves in the sand.

I laughed my head off, my Omani passenger got out of the car and hurled.

I had been trying to get hold of some high temp brake fluid for the event but failed. Of course Herr Fritz the instructor who by then had completed the next lap stopped to help out and duly came out with the "I told you ze 928 does not handle zis way". When I told him I had entered the bend at 100 mph wth no brakes I suggested he should try doing that in a 911 and see if he walked away from it.

It amazed me just how much control the 928 allowed me in what was in reality a totally out of control situation. Our cars really have a lot of inherent stability that most do not get a chance to experience. Doubtless as someone who has been sideways at 200 mph you will appreciate that better than most- at least you had a parachute!

Rgds

Fred

mark kibort

fred,
exciting stuff, but the car should never get in this kind of sitation and the fluid should never boil.... so funny, how during race weekends, 50 cars will race vets, vipers, m3s, maseratis, porsche etc, and not one guy will boil his fluid..... go to any driving event, and half the field is complaining of soft pedal or boiling fluid. yes, the 928 is good in a panic situation though and good for you you handled it well. when you go out there again. there is no smoothness points for braking. go hard on the brakes, when ever you need them and get off as soon as you can, or relase a little later in the turn entry for trail brake effects if you can. (make sure you focuse on braking straight). you will find much more speed and a much reduced chance of boiling fluid!

let see some incar video next time!!

FredR

Mark,

It was a bit of a one-off situation and certainly part of the "learning curve".

I knew it could happen and was concerned it might, but nonetheless was not pushing the brakes hard at all or so I thought. What I suspect in part caused the problem was that after every lap they stopped for a minute or so as we changed line up so possibly things got a bit heat soaked. Add to that I was driving an automatic and in fact had to keep braking to avoid whacking into the 996 in front of me when in reality I would not normally have hit the brakes at all and you get the picture. The brake fluid was fitted by the local agents and was relatively fresh so I figured it should suffice without boiling. Of course with wider wheels one has more traction for braking and I had Hawk Plus pads fitted for extra bite [more heat generated] and a higher pressure [33 barg] rear bias valve so was keen to test how that worked trail braking wise.

As you say the simple fact is that we have to slow down something in the region of 200kg extra compared to a 911 of similar vintage and that was the first time I had taken an auto tranny on the track. In my motorcycling days on Briitsh bikes I think the gear box did most of the braking- miss a cog and you were screwed braking wise!

The thing I learned quickly was that putting a 928 on the track, although not too difficult, still requires careful preparation and things can and do go wrong very quickly if you do not prepare for such correctly. the notion that you can put these things on a track without preparation may hold to some extent if running in stock form but once you start going down the modification route you have to have the package "well balanced" as you regular track stars will no doubt well appreciate.

Interestingly after that event I had a 450km drive back home that evening and on the road the brakes never missed a beat despite moving it along at times.

The track is a different world- plain and simple. You'd love driving the Autodrome up in Dubai- it is an excellent circuit to drive [when the brakes are working].

Rgds

Fred

Carl Fausett

Thanks Mark - I did not realize your racer was of the non-pinned school. Good to know. So your alignment info might be more applicable to another non-pinned car than mine.

Last time I boiled fluid was Pike Peak - I boiled the power steering fluid! 156 turns in 12 miles at altitudes of 9,000 to 14,000 feet will do that. Boy were my arms burning at the top! Installed a small power steering cooler and changed to synthetic PS fluid and problem was all gone.

mark kibort

i can only imagine... be really hard to get to the edge knowing what lurks on the other sides of the road! PS fluid sounds possible, and probable as thats a lot of turninig! over 60 turns for 12miles at most tracks, so double the turns. a lot depends on the turns. I run near 200 turns in a 30min race at Sears and its non stop braking and turning. never a time to even check the tach.. all feel. im beat after Sears! (by the way, that's 324 very hard upshifts and downshifts per 30min race)

im still wondering how the pinning will effect the alignment settings, as far as camber . doesnt the weisach toe in on compression or droop? if so, thats the reason that i like 0 toe in the rear due to the way the car gets very tight if there is any toe at all.

KenRudd

Just to keep the thread current, I now have the following settings:

Front Camber: -2.5L, -2.5R
Front toe: 0.08L, 0.08R
Rear Camber: -1.8L, -1.7R
Rear Toe: 0.11L, 0.16R

The Event at Charlotte on 10/31 was cancelled, so next track day is 11/13. I will post results/impressions.

mark kibort

size tires. rims, weight of car?

thats way too much camber in the front and adequate in the rear.
ideal is: 1.5 front and 1.8 to 2.0 rear... .1 toe front and .1 degree rear.

your total toe in the front is .16 degrees?
total toe in the rear is .27 degrees?

I have one of the best handling 928s i think ive ever seen from video, fastest based on times (without a modified engine ) and over 20 years of track data. I dont know why anyone would track a car and not use my settings as a starting point, ESPECIALLY since my settings has resulted in fast lap times and really nice wear patterns on the street using only DOT race rubber.
when i started racing , that's what i did.. I used someone's settings that was running fast, and started there. by the way, He ended up backing down the camber on the front and rear and had a better handling car because of it and better wear patterns. (not burning up the inside edge any more)

too much toe in the rear will make the car feel tight, especially with the weisach not being pinned. it will add to a push feeling and make the car hard to rotate. you are at the low side of the 928 alignment spec, so the toe should be ok.... if you track a lot, you might want to go less in the rear. however, if your car has a real soft suspension, it will work because under braking compression, the wheels toe out due to bump steer,and that helps the car be more stable under braking... with a stiff suspension, this is not an issue

KenRudd

MK-
Front 235/40/18
Rear 275/35/18

Your Toe numbers are correct.

Weight ~3,525 including driver and ~1/2 tank fuel.

So you recommend dialing back out about 1.0 from the front?

mark kibort

so, toe is in spec, but it might be a little tight with that amount of toe in the rear, but at your weight (near stock) it shouldnt be that big a deal.... especially if you are not running DOT race rubber. tires are good in the rear but a little on the small size for the weight of the car up front, so that will make the car push a little. so, absolutely get some of that camber out of the front... not going to be a huge handling issue, but you will wear the inside edges much faster.... if the suspension is real soft, the camber will help a little , but again, i think you are going for dual purpose (street , track) so back the alignment down to 1.2-1.5 in the front. 1.5 is fairly aggressive for the 928 anyway.