924Board.org

[daniel]

Hi All
I have not been able to race my car properly for about 18 months now due to ongoing mechanical issues, but on Friday all of this came to an end and I was able to run my car in a practice day. Mechanically the package worked well and I must publicly thank Ideola (Dan) for his ongoing help in sorting out my engine and gearbox dramas. It is the sign of a good reseller when he stands by his products even if things dont go according to plan.

The problem I have is with the suspension setup. I find the car reasonably good around fast sweeping corners, but tight corners are a different matter altogether. At one point on this track there is a very tight left hander that completely changes direction, at this corner I can not get the car to the apex at all and I am applying a lot of lock.
The other problem is the car seems unstable with rapid changes of direction and has a tendency to lock wheels under brakes unless it is pointed dead straight ahead.

The suspension setup is as follows:
400lb front springs
28mm rear torsion bars
24mm hollow front sway bar
18mm solid rear sway bar
bilstein shocks all round
Urethane front sway bar bushes, all other front bushes are delrin
All rear bushes are rubber, but in good condition
Professionally aligned, 2deg neg camber all round and wheels pointing straight ahead (no toe in)

I have a set of 280lb springs, I had the 400lb'ers made after a experienced racer suggested it to me at the last meeting I attended.

Things I can try:
- Dial in some toe in into the front
- Refit the 280lb springs
- Have even softer front springs made (say 230lb?)
- It has been suggested to me to run the car with no rear sway bar, or return to the smaller standard bar that came with the car (77.5)

Things I can not try
- The rules fix maximum neg camber at 2deg. This is to stop people modifying suspension
- Standard suspension must be retained, i.e. no coil overs, no adjustable shocks, no fitting 5 lug suspension etc
- I dont want to fit different rear torsion bars at this time, by the time I wait for the bars to arrive from the US I wont have time to fit them before the next meeting, but I could consider this for a future option.

Any advice is appreciated!

Thanks
Daniel
_________________
Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet

[leadfoot]

Locking of the brakes will be a factor having no ABS, so you will need to address your brake bias somehow. Either by adjusting the size of discs and pads front to rear or a bias valve to allow you to change the ratio.

Just to clarify you're getting front understeer?
Increase weight transfer at the rear by increasing rear roll stiffness
Reduce weight on front by reducing front roll stiffness
Reduce front toe in - N/A
Increase aerodynamic downforce on front tiires
Reduce aerodynamic downforce on rear tires
Use wider front tires.

Although your not allowed to change toe, with the nature of our cars toe changes with the suspension height changes, maybe why your racer friend suggested the 400lb springs.
There is a bump steer fix that will alleviate the toe in/out scenario by adjusting the height of the tie rod in relation to the steering knuckle. My preference would be to have some rods machined as extensions twith the correct tapered end.
Stu
http://www.924board.org/viewtopic.php?t=21774
http://www.freisinger-motorsport.de/porsche/uk/Porsche_Restoration_Detail/2935.html
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[Rasta Monsta]

For sure, car is imbalanced. 400/24 hollow front does not match 28/18 solid rear (remedy with 30mm rears).

Not enough damping? What Bilsteins? If they are HD, they cannot handle the spring rate you are running (remedy with Koni Sport).
_________________
Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[daniel]

Understeer is correct, from what im gathering from both reducing the front spring rate would be a reasonable place to start? If so would reverting to the 280lb springs be enough or perhaps I should go even lighter?

Also I can change front toe, just a simple turn of the tie rods? If I had my head screwed on I should have done it at the track on Friday.

Stu, no downforce is allowed and I am stuck with the standard wheels and 225/60 r14 tires
_________________
Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet

[Raceboy]

But 924's came also with 15 and 16 inch wheels, 5lug setup even on 2.0 NA cars as M471 option, why don't the rules allow that?
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche

[Cedric]

Its very tricky to say anything about the balance if we dont know the tyre widths you run (what kind of tyres, 225 on standard rims sound very interesting, must be slloppy as hell?). I assume you run with the same width all around?

It is in general very soft for being a race car, going to 280 is street car soft. Alot of suspension movement is not desirable since you get camber changes that lessens the grip, aswell as giving the car slow reactions.

High speed instability can be bacause of lot of things, first of all you should have a slight toe in at the back endto get it stable at high speed and under braking. A slight toe out up front will get you a quicker turn in but also give you a more neervous car at speed. I run a little toe in at the back and 0 at the front on my car. Dead stable even at 230km/h. I would also run max caster if that isnt fixet yet, that will give you a slight more negative camber when you turn the wheel at tight corners. And thus get you more front end grip, downsides is a little bit heavier steering at full lock.

Have you had the car in for a corner weight setup? Try getting the diagonal weights as nice and possible, this can severely affect braking. I assume the brake system is totally rebuilt.
I noticed the na brake bias to be pretty good with sticky R-compunds on, with sloppier tyres it could feel a little to conservative with the front bias. Installing adjustable brake bias controller could be something but it should work pretty ok out of the box. If cylinders are stock.

Is the understeer present in both dynamic and statical corners loads? Is the car statical balanced? If you always understeer maybe you could try a 19mm adjustable rear bar to try to dial in the balance. Is the car responding to "throttle lift of" mid corner? You could try to up the damping a click or to at the rear if you dont get reaction enough.


Crap, just re read your post and realized you are very restricted suspension wise.

But dont change to toe in at the front, dont go to soft at the front.

I run 350/ 28 (weltemeister adjustable solid bar) up front and 28 bars / 22 sway bar (adjustable as well) at the rear. -3 camber front and -2 something at the rear. 0 toe front and slight toe in at the back, max caster up front, around 3 degrees if i remember correctly. 205 15" sticky tyres. It is a very balanced car, but adjustable sway bars is the trick when you dial in race car balance. Its not at all stiff enough for being a race car( which its not). But you run on balloon tyres so that limits spring rates somewhat.
_________________
1980 924 Turbo
www.instagram.com/garagecedric/

[john h]

Daniel,
I'd add a little toe in at the front for stability, in addition if you can do it on the back wind the trailing arm adjustment right down so when you look at the sill of the car the sill's tamper down at the back getting the rear of the car lower than the front. This especially helps with the weight transfer under braking. Another area to look at regarding brake lock up is to re-plumb the brake lines so the front brakes come of the same circuit and rears off the other. The 924 comes with left rear right front on same circuit and if you lower the back this mod will increase front braking efficiency and reduce lockup.

The front bar sounds about right anything bigger and you’d find it hard to turn in, I run a 25 mm front bar (turbo was 25mm) and an 18mm rear bar (turbo had a 16mm bar), in the wet I disconnect the rear bar droppers (i.e. running no rear bar). In this set up I’ve found it handles well and suits my driving style. Tried a bigger front and rear bars and didn’t really find it suited my driving style. Torsion bars sound a ok as well I run an aftermarket 25 mm torsion bar and also the 250 lb. springs (a bit soft but I found harder ones didn’t get the car to go around corners etc.), note these are also a good 50 mm shorter than the GT spring I had originally, hence the car is a lot lower than a “normal” 924/924T.
The front springs might be a bit hard but again this is a bit dependant on the driver’s style and also the track conditions.
Shame you can’t change the front camber a bit – I run 3 to 3.5 degrees negative and while it does chew the front tyres inner edges out quickly a swap of tyres on rims allows for equal wear. To get the extra camber you need to slot the stub axle / strut bracket a bit but you’re not allowed to do that by the sounds of it.

One thing I noticed in the past was the type of tyres you are running can affect straight lien stability. When I ran so brand new Bridgestone RE71R they were the super grippy road race tyre rather than the RE71 road tyre and first time out the car was very unstable so much so I changed back to my old worn tyres. Before the next meeting I had about 2 to 3mm skimmed off the tread (still left 2mm tread) and lo and behold no other changes same suspension setting, same tyres pressures same track and the car was ultra-stable in a straight line.
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Remember a Porsche is not just for Christmas,

if you take it to pieces slowly it can provide anguish all year long!