dialing in the front end ?
 

HUH?
alright.
my car is a bastard of bastards (ask the gruppe b guys...they seem to agree)

the car is driven on nice days, and sometimes during the summer is a daily driver. It is has been auto-crossed 5 times now, and those were every event avaible to me. IT WILL SEE some DE events and alot more auto-x.



75 911s body, coupe, non-sunroof.
i am running carrera sway bars.
18x9 front, 18x11 rears
235/265
the front torsion bar is not stock, i believe it is up 1mm from stock...changed it 5 years ago now when i we intialling learning how to do anything.....so i think that makes it ~19mm?

2 year old blisten sports all around.

during the last set of engine changes i upped the rear TB's to 29mm, even though i swore that i ordered 28...
anyways, the rear feels very good, step out is progressive, very little squat. ride is better then expected, and more then good enough.

the front feels un-planted during hard acceleration. I feels like it scrubs during tansition turns. Also on wide sweepers it feels as if it is loosing grip long before the rear does.

now, the car is lighter then i ever expected it to be, or that anyone here or else where told me it would be. i have measured at two different federal scales...and came in very similar. first was 1230kg's with a passanged, and our golf bags. later was me and a car full of stuff (desk pieces, cpu..) came in at 1180, both time i was in the car, and it had mroe then 3/4 tank.... i have removed some weight, but it is all steel....

anyways, i plan on adding a tringualted front brace. I am on a very tight budget. I am in the process of deciding how to remove some weight from the rear with some fg pieces and a tail delete.

car dynoed @ 278rwhp, with the given weight thats ~8.6lbs/hp....pretty nice ratio and it feel crazy fast.... it brakes well and once budget permits will be given a big boost there, but already has the 23mm MC and stailless lines, along with some fancy cheap upgrades..

sorry i will clarify more in the morning, am getting sentenced to bed at the moment.... key areas that i need to clarify would help me explain it better....

sorry and thank you
Nick

I'm not sure if there's enough information here to come to a positive conclusion, not to mention set-ups also depend on the driver and driver's "style".

This could just be a function of the load transitioning to the back under hard acceleration. Your best bet might be to switch to adjustable front shocks, or have the existing shocks revalved. Either way the objective might be to reduce the rebound dampening. This will allow the front wheels to settle back down to the ground faster when the front end lifts under acceleration.

I'm not quite sure what you're describing, but going softer on the front rebound might help with this too. But as I said, I can't really picture what you're saying. It might be easier if you described it in the following fashion:

-- Corner Type: Fast/Slow/Medium? Increasing/Decreasing/Constant radius? Uphill/Downhill? Series of linked corners (S's)?

--What is happining in each phase of the corner?
- Corner Entry - Turn-in until you pick-up the throttle
- Mid-corner - during balanced throttle portion of the corner
- Corner entry - Apex to track-out, under WOT.

What have you done about the alignment?

Joe

Re: dialing in the front end ?
 

John's questions are good.

But if I can add some speculation in the absence of more information:

278 RWHP has a habit of doing that ;) When cornering hard, these cars steer with the throttle as much as the wheel, you may just need to get more experience with this.

Less throttle means more weight on the front and more stick, more throttle lightens the front. Use the throttle to modulate this.


What is your ride height? and have you trimmed the bump rubbers?

Sounds like your front tbars are fairly soft (but it would be helpfull for you to know for sure what you have). You may be bottoming out the fronts, riding on the bump stops. If that is happening, the front will loose grip abruptly.


Again, answers to John's questions would be helpfull.

One other question I was meaning to ask -- what sort of diff are you running?

hey
thanks for the replies, will try and use this picture of the course layout from a few weeks ago to describe the 'feelings'


-my ride height is as low as i can go w/o rubbing the tires, however that was before i pushed up the inside of the fenders.

- i have not trimmed the bump rubbers,

accidently hit post...

moving forward then...
http://forums.pelicanparts.com/uploa...1166132087.jpg


-the alignment is at much chamber as i can get. in the rear i believe it is at -1
and the front's seem practically upright.
the car does not have raised spindles.
- tranny is a 915 open diff. has been rebuilt.

- in constant radius sweepers like @ station 3, under increasing (smoothly) throttle the front feels very light, and not at all condifence inspiring.
Though i have measured (consistently) the highest speed on the back straigh away.

I defiently need to get used to the power, sometimes when talking with my friends i wish for more....but never in the car do I.

station 1, which is actually a much tighter turn then it looks (pictured here):
http://img321.imageshack.us/img321/2...0391lv7.th.jpg
i find that i am under-steering, expecially on turn in, however it persists into mid corner, and once exiting getting the car to rotate with the throttle is easy (though scary).

when entering station 2, where i placed another 2, there is a crest right at corner enterance. aside from horribly upsetting my car it also creates under-steer, no matter how slow i take it.

exiting station 4, after hard (threshold) braking i find that, probably due to my over braking, turn in is okay, however tranisition back onto throttle induces some under steer and a floating feeling up front.

few other notes, even when doing consistent laps (well 4 in a row) my tire pressure never seems to go up, and i am running considerably lower pressure then everyone else there, w/o any sidewall roll over...probably due to the stretched tires.

at the hair pin in station 2 which troubles many other cars mine is fast through. it is the only place in the course i go back down to first, and i find i am fastest through that section when making the corner a decreasing radius corner, starting as high and late as possible and 'diving' into it.

undoubtly the place where i could gain the most time is with training myself, however i feel that a more confident inspiring front end would help this also.

hope this helps explain the situation a little... either way i'm probably going to up to 22 front tb's or if i can find some money rsr style coil overs with raised spindles...thats the dream.... and of course the tringualted front brace....

do turbo tie rods realling improve anything? mine seem fine.... and how about the bump steer kits?

just trying to figure out how to make the car more user friendly.

thanks
Nick

Since you also have stock spindle height, and soft front tbars, I will speculate you are bottoming out the front. This will cause abrupt changes in the grip of the front end.

You can test this by putting a zip tie on the chrome part of your shocks, letting the slider push it. Best to put it on the rod that passes through the bump rubber, though this is more work. It will stay at the farthest position.

You can address this problem with a combination of methods:

- Stiffer tbars
- Increased ride height
- Raise spindles
- Cut down bump rubbers
- Stiffer sway bars

Consider that your front shocks only have about 3 inches of compression at stock ride height. Part of that is in contact with the bump rubbers. If you've lowered the car say 1.5 inches, you don't have much travel.

Something to consider is that as you drop the car's ride height, the front suspension geometry lowers the front roll center, potentially below the track surface. What this does is it creates a bit of a vicious circle.

1) Lowering the front roll center more then the ride height drops (because of the geometry) will make the front suspension act softer in roll. Which can make it bottom faster and thus cause understeer.
2) Dropping the front roll center far below ground level will also cause the front of the car to jack-down under cornering -- thus further causing the car to drop onto it's bump stops (see point 1 above).
3) For geometric reasons, you also tend to loose camber, which means that when the car rolls (see item 1 above) you will lose camber against the road, which will make the car understeer.

There are two ways to address this:

1) Massively stiffen the front end springs and sway bars (see my signature below) .
2) Raise the front spindles, so that the front geometry returns to it's intended range. Once you do this, the car will be even lower then it is now, but if I were you I'd return it back to it's current ride height. You'll then need to corner balance and align the car again. I suspect that you'll find that you've recovered a lot of the front camber in the process. You can get your front struts re-valved as I originally recommended at the same time since you'll have the struts off the car.

My suggestion is to adopt option 2.

Drive the car like that for a little while and see how it feels. I suspect that you'll find that the car will now be roll-loose, because the rear roll centers will be relatively low compared to the re-optomised front, and tend to squat more while accelerating out of corners. If that is still a problem, I'd recommend getting the adjustable rear trailing arm pivots that allow you to raise the rear roll centers. Alternatively you could also just go massively stiffer on the rear T-bars and sway bars, but once again that will be a crutch as opposed to fixing the real problem which is geometry.

Note that the approach that I'm recommended is partially what the factory used for the Carrera RSR's and the Turbos.

I have the exact same symptons. My car a 1982 SC 23/30TB's ,Bilstein Sports all around, stock SC sway bars, turbo tie rod ends and spacers in front rack as bump steer kit. Autopower 4pt rollbar and front brace which helps some what stiffen the car. Stock motor. Car lowered a little more than european height

Coming into say a fast right hand sweeper. Car is flat and front is planted coming in.Start to feather the throttle on. Begin to hit some bumps mid entry, front starts to skidder and develops a outside push, slightly feather off the throttle front begins to grab and turn inward towards its rightful direction. Back and forth with the throttle while trying to hold the steering wheel steady. Finally on the beginning of the exit full throttle. The car also does this in slow sweepers too while full on throttle. Cars front constantly skips over bumps slow or fast. :confused: This is my first 911 so I have nothing to compare to...

Dan

I can dail in all the camber I can get on my ride and still end up killing myself on the road if I neglect a minor detail- like the toe.

thanks for all the replies.

i should note that I am not the one adjusting my alignment. It is my mechanic who is an extremely experienced driver/racer. We did re-index the front bars, and we had the car about 3/4" lower however we found that the tire was rubbing... right now its actually at a kinda street ride height, for sure lower then european, but the 18's grant some extra clearance.

seems like it is time for me to play the cost versus gain game.
-will probably start with a crutch, like a 22mm front TB, and once budget permits i will have the coil-over , raised spindles, and bump steer setup

- i would be willing to adjust my setup and play with various adjustable components, however i am actually at school right now, and have been for the last ~3 years, and w/o a garage it complicates things.

thanks again to everyone for their replies, very insightful.

You lost me, if you're lower then "European", how can you still be "street" since you've got the car lowered further then Porsche's suspension engineers intended?

Quote:

seems like it is time for me to play the cost versus gain game. -will probably start with a crutch, like a 22mm front TB, and once budget permits i will have the coil-over , raised spindles, and bump steer setup - i would be willing to adjust my setup and play with various adjustable components, however i am actually at school right now, and have been for the last ~3 years, and w/o a garage it complicates things. thanks again to everyone for their replies, very insightful.

It sounds like you're starting at the expensive end of the spectrum by replacing parts, especially if they don't fix the problem. If it were me, I'd put the car up on blocks for a week or two, and pull the front struts and have the spindles raised. It's a matter of cutting them off, jigging it up and rewelding them on. You don't need coilovers and it's most likely cheaper then buying new T-bars and then throwing them away when you move to coil-overs (if you ever do). Then put the front end back together and get it corner balanced and aligned (which you'd have to do if you replaced the T-Bars anyhow). I suspect that you'll find that the car handles a lot better.

well i guess that does make ALOT more sense, seeing as the car is actually off the road for winter salting etc....

and i will have a chance to work on it in a few days... this sounds like a good idea, can any machine shop perform this?

how much do i want the spindles raised? for what i remeber its 40mm for cars using more then 17'wheels?

thanks for the quick replies.