The 944 suspension consists of Front: Springs and dampers:

Fichtel und Sachs or Boge non adjustable dampers M474 Sport Koni dampers
part no. 95134303106, 95134303206 rebound adjustable

M030 Koni dampers part no. 95134303132, 95134303232 (rebound, height adjustable, stiffer valving)

Rear: Torsion bars and dampers Sway/Anti roll bars

Shock absorbers / dampers

Front Shocks

The front units have a small tab sticking off the top of the shock shaftPop the little black plastic dust cap off from the center of the top strut mount inside the engine compartment. Koni supplies a knob that fits on this tab (or use a vice grip). Rotating the knob counter clockwise increases/stiffens the rebound forces, rotating it clockwise decreases/softens the rebound forces. Match the setting side to side...in other words, if you put one turn of rebound stiffness on the drivers side shock, match it up with one turn on the passenger side. You'll generally have about 2.5 turns of rotation on the adjustment tab

Rear Shocks

The best way to adjust the rear units is to remove them from the car. You will need to remove the units bump rubber (needle nose pliers or by forcing a nail or the like through the small holes on the upper dust cover) and fully compress the shock. This will engage an internal adjustment mechanism. Once this mechanism is engaged, rotating the upper portion of the shock clockwise will increase/stiffen rebound forces, rotating it counter clockwise will decrease rebound forces. If it has never been adjusted before it likely will be on the softest setting. You should get 2 to 2.5 full turns of rotation Remember, your shocks may be on full soft or full stiff already, don't force them past these "stops".
You'll feel them, so don't force it past these points. Go through the complete turns to check. Stiffer is when the shock rebounds more slowly -- it's really slow at full stiff

Standard on the turbo S is 1-1/4 turns towards hard from full soft. I found it helpful to draw a cross on a hard surface and put a rod through the bolt hole to measure the turns. I then fully compressed the shock and measured the time to extend with a stopwatch making sure they were both the same. It is possible to adjust the shock while it is still on the car by removing the bump rubber and the lower mounting bolt, but for your first time you probably ought to take it off the car so you can better feel and understand the adjustment

Real world experiences:

On the rear I found that half a turn from full stiff was too hard and added an extra quarter which is better but I will probably end up with a full turn from full stiff. I've got the Yellow Koni's on my S2. For street, I found 70% stiff in front, 50% stiff rear is good. Stiffer on front causes the front end to understeer, and if you like high-speed (+120 mph) on rough secondary highways, the front will feel light because the struts aren't absorbing bumps. Stiffer on rear gets uncomfortable.
For the track, I use the same in front, and 87% stiff on rear. 100% stiff on rear will rattle your teeth and the car; feels like the rear end never settles down. Effect of rebound setting adjusts how quickly the suspension lifts.


A good way to determine if the car is balanced well is to find a big parking lot and drive in a circle slowly and smoothly increasing speed. When you reach the limit of traction, all four tires should squeal and loose traction at the same time (4 wheel drift). You should be slowly accelerating and under throttle. If you let off a little, the front should tuck in and decrease the radius of the turn. If you add a little more throttle the front should push a little and increase the radius of the turn. Do either too much and the rear will come around on you.

The key to setting the rebound is to match the weight transfer to tire grip to get the largest control range while in a drift.

The regular Turbo had a range of springs, depending on the tolerance group of the parts. These were marked by yellow dots (on the springs themselves). One yellow dot had the wimpier springs , while the "heavier" springs had three yellow dots. Two yellow dots fell somewhere in-between. These springs were 15.6 inches (396 mm) long uncompressed. If it had the M030 suspension, however, then it had P/N 944.343.531.01, spring rate 28N/mm, inconstant wire diameter 11.7-12.2mm 12.9 inch (329 mm) progressively-wound springs. The lighter spring had a one white and one yellow dot, and the heavier spring had two white dots and one yellow dot. Finally, the 1990 Turbo had springs P/N 951.343.531.03, spring rate 28N/mm, constant wire diameter 11.6mm, at about 14 inches (356 mm) in length. These constant springs went from one grey dot to three grey dots to designate the spring range.

If the spring rates are the same what performance difference does constant versus inconstant wire diameter make? The constant wire diameter will be stiffer than a variable or inconstant wire diameter. Varying wire diameters are frequently used on progressive springs. The smaller diameter wire will compress first because it has a lighter rate. Once you pass that point, the thicker diameter coils should produce the same rate on either spring if you had them on a checker. Porsche doesn't usually stamp part #'s on their springs, rather they identify them with paint marks. If you look on the fiche, different spring part #'s will say, blue, purple, yellow etc. No spring rate info on the fiche unfortunately and Porsche, as mentioned above, measures rate in Newton meters. Spring force at length 220mm is 3050 to 3250 N for the inconstant vs. 3082-3330N at 241mm for the constant. If I remember well, F = k * Dx, ie Spring Force = (spring rate constant) * (compression (+) or expansion (-) of the spring). Assuming that the cars are lowered to the same amount, which may be the case for the M030 cars, I would expect the longer springs to be more compressed than the shorter ones, thus amounting to more force necessary to compress the spring further. Is this what is called pre-loading? In effect, the longer springs are stiffer than the shorter ones. What the technical specs book does not reveal is the geometry of the springs, i.e. are they conical a la S2, or the usual cylindrical shape? I would expect the conical springs to compress more than cylindrical springs as the coils can somewhat "nest" in each other leading to more suspension travel.

Torsion bars are simply uncoiled springs. When a coil spring is compressed, the force required to compress the spring is a result of twisting the wire in the coil. If the coil is straightened and the wire twisted, the same forces are present. This is a torsion bar.

Because torsion bars are generally shorter than the wire used to make a coil spring and twist through smaller angles, they are larger in diameter than the wire in the coil spring.

The spring constant of a torsion bar (the amount of force required to twist the bar through a given rotation) is proportional to the diameter of the bar to the 4th power.

Here is a table based on suspension geometry measurements and some calculations to get effective rear wheel spring rate as a function of solid bar diameter (or effective hollow bar diameter):


The Turbo S (and the S2) has a 26.8 mm front tubular stabilizer bar, up from 25.5 mm of previous Turbo's. At some point in production of the 89 turbo they changed the rear sway size from 18mm to 16mm to "enhance stability" (IE more understeer).


The rake of the North American 924/944/968 was set with the tail slightly higher than the nose. This was done to meet U.S. bumper law requirements. Porsche had intended to (and I think the Euro cars are) set the nose and tail to the same ride height. Setting your car to that specification maximizes the braking by reducing nose dive. The rake was intended to be set so the lower edge of the rocker panel was parallel with the floor of a level garage. How low can you go? 2 phrases: ball joints and suspension travel

The ball joint should not bind and you definitely don't want to run out of suspension travel 13 to 13.5 inches from the front wheel centre to the bottom lip of the fender/wing or front: 130 + or - 5 mm as measured from the head of the bolt that attaches the caster blocks to the body to the ground. rear: 230 + or - 5 mm, as measured from the center of the torsion bar housing to the ground.

Adjusting Height

Front Height Jack the car up and remove the wheel. Clean the threads on the struts threaded collar. You don't want any dirt galling the threads when you move the perch There is a lower spring perch that the spring sits on and a lower jam nut that locks up against the lower perch. (NOTE there is no jam nut on the 968)
The theory is that once you have the lower perch where you want it you lock the jam nut against it to keep it from moving.
Normally the lower perch and jam nut are loosened/moved by using a C spanner (you can also get a special tool). You don't have to use one though. I usually just get a brass punch. Use your punch to loosen the lower jam nut from the spring perch (turn it clockwise when looking down on the nut).
Once the lower jam nut is loose, screw it down the threaded collar a bit to get it out of the way. At this point, make a mark on the lower spring perch so you can count the number of turns you rotate the assembly so you can match it up on the other side of the car.

Then just grab the spring with both hands and rotate it counter clockwise. Count the turns. Once you've got it where you want it, lock the jam nut against the lower perch and set it with your punch Measure front ride height from the head of the bolt that secures the caster block to the car to the ground. This is also what the factory says to measure as described in the 951 service manual supplement.

Rear Height

Car Spring Brace Setting

All 968 CS 14.0 deg
All 968 CS M030 9.0 deg
USA Coupe 18.5 deg
USA M030 14.0 deg
Stock 951S 18.0 deg

The good news: It can be set using the eccentric ride height adjusters. They are located on the spring plate just rear of the torsion bar.

The larger "nut" is actually an eccentric. It will raise or lower the car by about +/- 11/16" It is torqued to a high value so it will be hard to break loose without a good sized breaker bar.

1. Jack car and place on stands.
2. Remove wheels.
3. Remove anti-roll bar drop links on both sides
4. Mark position of the adjuster on the spring plate. Don't scribe - use paint. This will give you an idea of how much you are moving the plate.
5. Have to loosen both the nuts on the eccentric and normal bolt, each 14mm so the plate can move relative to the fixed mount. Requires a 36mm open-end wrench on the head of the eccentric and a 24mm open-end on the normal bolt. If the nuts have been loosened before replace them. If the nuts or the bolts are corroded replace them. Replacement of the forward-most bolt requires removal of the torsion tube.
6. The rear-most of the two bolts is an eccentric. This is the one with the 36mm head.
7. Adjust ride height to suit by using a 36mm open-end wrench on the head of the eccentric.
8. Apply anti-seize and torque the nuts to 181 ft-lb.
9. Repeat for the other side.
10. Re-assemble, drop the car, test drive, etc.

The bad news: If further adjustment is required the torsion bars will need re-indexing. In the 944 the bars are encased in a transverse tube. Splines on each end of the bar engage splines in the center of the tube and in a movable "spring plate" located on the outside of the tube that attaches to the trailing arm next to the stub axle.

There are a different number of splines on each end of the bar and these allow a sort of vernier indexing of the spring plate on the end of the bar to achieve the desired ride height.
The outside has 44 splines (teeth)

Every tooth you move the outside splines you move the spring plate about 9 degrees.
The inside has 40 splines (teeth) Every tooth you move the inside splines you move the spring plate about 8.2 degrees.
If you move both the inside and the outside one tooth you effectively move the spring plate .8 degrees (the difference between the 2)

.8 degrees works out to 6.4mm or about 1/4" Here are resources for replacing/re indexing torsion bars:

Article by Craig Seko

Texts by Doug Donsbach and Marc Belange

944faq

Working alone without a lift will take you about 8-12 hours. For the rear, measure from the center of the torsion bar outer tubes to the ground.

Camber

Increasing the negative camber gives improved turn in and counteracts the tyres rolling in a corner
Front

Alignment: - 0.5 camber to -2.0

Rear
Set with the eccentric bolt that is one of the three 12mm bolts holding the spring plate to the trailing arm. The eccentric bolt is also the mount for the sway bar drop link. Requires all three 12mm bolts to be loosened. Rotating the eccentric causes the trailing arm to rotate where it attaches to the spring plate. Replace the lock nuts after a couple of cycles. Torque the nut on the eccentric to 66 ft-lb and the other two bolts to 76 ft-lb when finished. Alignment: -1 to -1.5 camber. Toe Set by loosening the 12mm bolts described above and using a special tool inserted into the hole located to the rear of the camber eccentric. This tool, when rotated, causes the trailing arm to move slightly forward or rearward on the spring plate. The special tool is not essential as long as you are careful with the motion. Torque as above.

In broad terms if you stiffen the front the car will understeer and making the rear stiffer will make the car oversteer, so when upgrading try to balance the additional stiffness. Please don't fall into the trap of setting the shocks stiffer to try and compensate for lack of spring rate. The suspension ends up over damped and will hop (especially the rear) Almost all Turbo's from 1988- came with M030 Koni suspension (yellow) which is a very good setup. If it came with the non-adjustable Sachs/Boge (black/grey) shocks - get rid of them!


So the options are: Increase front spring rate by changing the springs Increase rear spring rate with helper springs on the shock or larger torsion bars If you use helper springs it will raise the rear a lot: reindex the torsion bars or try some shorter, stiffer springs to see if you can get the ride height you want. Also to calculate the effective spring rate add the torsion bar and the helper spring rate e.g. 25.5 torsion bar and 100lb helper 175 + (100 * 0.65) = 240lb effective rate Other choices: Add a real coilover setup of your choice to augment the stock torsion bars. Pull the torsion bars and add a full coilover setup. If you pull the torsion bars and do nothing to upgrade the stock rubber bushings for the spring plate you could end up with worse handling, not better. The reason is without the torsion bars to add support to the spring plate attachment, you'll get a lot of movement during cornering. It's precisely this suspension movement that makes the 944 a handful at times on the track.

Another consideration is more noise and roughness transmitted to the body structure through the upper shock mount since the coil spring and shock are now supporting all the rear weight. I can't quantify how much increase you will feel but Kelly-Moss Racing says it is noticeable.

Increase sway/anti-roll bar diameter

Lower the ride height

Don't forget tyres!

Some real life opinions:

It is very important to choose spring rates wisely. If I were going to increase the front rate only for a street/race/AX car, I'd go no higher than 250-275. I believe that you can decrease the resulting understeer
cost-effectively with a stiffer sway bar. Beyond this point, I think you have to increase the rear spring rate. I run 450 lb front springs, with the Turbo S (25.5 mm ) torsion bars and 200 lb helper springs on Koni/968 M030rear coilover shocks.

Let's presume there are five levels of suspension for a 944 Turbo. These are:

1. 944 Turbo stock Fine on the street, but certainly not that great on the track unless it has the M030 option. Everything is much too soft for good track use. My non-M030 S2 falls into this category. Yeah, you can drive it on the track and go pretty fast, but it's not easy to keep it under control.

2. 944 Turbo S stock Not as bad as you might think. Really a great setup for the street and quite fast on the track for a car with pretty soft springs. The fronts are only about 160 lb/in and the rear bars are roughly equivalent to 175lb/in wheel rate. Nevertheless, there are still club racers that run these cars in nearly stock form and go very fast. Driver skill plays a major roll here of course.

3. 944 Turbo S Cup The cup cars use a Bilstein suspension with springs running around 160-410 variable rate in front. The rear shocks use helper springs but I don't know the wheel rate. The shocks are VERY stiff. Front sway bar is 30mm and rear is 22 mm 3 way adjustable

4. Aftermarket 944 Turbo still (barely) streetable For this you could run something like 400 lb/in front springs on turbo S or aftermarket Koni double adjustable M030 type struts and aftermarket perches to fit 2.5" diameter springs. Fit 30 mm rear torsion bars or coil-overs and sway bars of your choice.

5. Aftermarket 944 Turbo not streetable Greater than 400 lb/in front springs with greater than 30 mm bars or full coil-over rear suspension with very stiff springs. The main thing that would make the Cup car not streetable is the shocks. Others run the Cup car front springs on their street cars with 29 mm torsion bars and seem to like it OK.

The universally recognized components of the level 4 and 5 suspensions are very stiff springs and shocks and sway bars. I would also put full spherical bearing suspension components in this category.

Is the 944 Turbo S Cup suspension the last word in streetable but near-race suspension setups? A true Cup suspension is a race setup. It's not the best you can do today but in its day it was fast. Today you can fit Penske struts or JRZ and probably be faster, and there are better suspension bushings and A-arms too. At the track the Bilstiens are a better choice. In particular:

Front
AK-1120 Threaded Body with Valving 600/190
AK-1121 Threaded Body with Valving 600/190
Rear
AK-37354 Threaded Body with Valving 565/218

These are out of the box a bulletproof set up, if you tracking the car a lot I would recommend removing about half the bumpstop on the fronts. (takes about 10 minutes). I know guys that have been running this set up for 3 years 6-10 events a year, and they still perform like new.
Stay with stock front swaybar and start with some 600 springs with helpers.

968 CS (M030) suspension is very similar to the 951S. They use the same front springs and similar struts with threaded collars. The rear torsion bars are the same 25.5 mm but the CS uses rear shocks with barrel shaped helper springs (non height adjustable) to stiffen the rear slightly compared to the 951S. Sway bars are 30 mm front and 19 mm 3-way adjustable rear compared to 26.8 mm front, 16 mm rear fixed on the 951S. This is a very nice street package.

Jon Mitchell Basically, its the same as MO30, top adjustable Koni's, but valved with a slightly wider range, going from almost the same valving as the standard F&S S2/968 struts at the softest end, and a fraction softer than MO30 (wound up to the hardest setting) at the hardest setting. Instead of the MO30 type platforms for the springs, ours used platforms made to utilise standard off the shelf 2.5" ID coil springs, as used as an industry standard for coil overs in motorsport, and are available in any spring rate you want. We also used a solid top mount, fitted with a spherical bearing, and made adjustable in for camber and caster. (so these settings can quickly be changed to exactly repeatable positions in a pit lane, without complex geometry equipment to get both sides equal and able to move back and forth between several positions.) All the aluminium parts (threaded collars, perches, lock rings, top mounts) were designed and machined by a local company that supplies chassis and suspension systems to indikart and nascar racing in the USA



Strategy-wise: I think you want to consider a Yes/No on the following:

1. Ride Height Adjustability (front and back) I think its important. If you agree, get struts and dampers with adjustable perches/seats. IMHO this *in practice* means you will need to lose the Torsion bars... see 2.

2. Torsion bars/Coilovers/Both I think keeping the torsion bars is inconsistent with height adjust because its not really controllable without a lot of messing around... you have to drop half the car at the back to get it adjusted outside a pretty narrow range. Some people don't like the idea of losing the torsion bars either they feel its unnecessary or they are worried about localised stress on the chassis where the top mounts are (underneath beside the fuel tank). I have full coilovers (Carrera from Huntley) and they work well... I have heard anyone actually using coilovers identifying an actual problem with cracking so it remains a theoretical possibility to me. Torsion bars may be required by the regulations in some race series in the US and elsewhere. Also losing the torsion bars will enable you to change spring rate fast, with T bars, you could change helper springs rates but you'd have to mess around the ride height when you do it.

3. Narrow Springs - race springs are most commonly 2.5 inches internal diameter OR 60mm. If you get struts and damper capable of seating such springs you will have a wide choice of lengths/poundages. Also narrow springs let you run wider wheels.. e.g. 10" front and back or even 11" at the back To me, if track dominates road... its a no brainer. Lose the bars and replace struts/dampers/springs front and back.

On a 1988 951 I have driven the stock bars and springs, solid 28mm/250lb and most recently hollow 33mm/425lb (33mm hollow with 19mm bore is 32mm effective) and I can say that these are decent matches. The 250lb springs are likely progressive and I think a 29mm solid bars is probably a better match than the 28mm. The decision between these two diameters will be determined by sway bar selection and personal driving style. The28mm bar will understeer more than the 29mm bar at the limit (all else equal).

By way of reference, I went from the factory stock bars and springs on my '88 951 (non-S) to a 28mm solid/250# progressive spring setup a couple of years ago and then mid-season this year went to a setup that included spherical bearings on all mounting points and 33mm hollow/425# linear springs. This car is a lot of fun to drive right now Dropping the rear with the eccentric bolt at the spring plate, Torsion bar rates to match front coil spring rates, sway bars etc. A cheap effective setup is 250lb front springs, drop the rear with the eccentrics, add Weltmeister bars front and rear, front strut mounts, a strut brace and get some Kumhos and with proper adjusting at the track, you will handle 90-95% as well as most race prepared 944's.

Front springs

The factory spring perches of different diameters accommodate the conical springs well but makes using others difficult. You may want to replace these with standard

968 M030 Rear shocks

There is a Koni coil over shock for the rear. This carries a Porsche part number from the 968 M030 option. This combination was intended to be used with the stock rear torsion bar. The spring has a free length of 7 inches and 6 inches when mounted on a fully extended shock The addition of the coil springs significantly raised the back of the car thus requiring us to lower it by the torsion bars. We rotated the shaft 2 teeth on the outer spline. There are 44 splines on the outer side. This changed the geometry 16.4 degrees or approximately 3". Since the spring on the shock would now be supporting some of the weight, we ended up lowering it about 2" when completed. The 968 helper springs are 120lb and are 60-65% effective at the wheel so 70lb/in You can change the Porsche barrel springs to shorter, stiffer racing springs. This will get the ride height down and stiffen the rear. If you are going to move to 300lb springs in front you will need at least 275lb springs in the rear to balance everything. Unfortunately, the springs you can fit to the 968 M030 shocks are not that long, and you may find that you can't get the suspension travel you'd like to have. That's probably why Porsche used those weird barrel-shaped springs in the first place. Measure travel with putty Upgraded Bump stops I have the 3012 Koni coilovers and I can tell you they are anything but weak. The valving used for the Paragon setup is the 3rd stiffest offered by Koni... normally for spring rates between 500 and 3500 lb/in. Isn't that enough?

I run mine full soft on the street with 24 mm torsion bars and 275 lb/in helper springs. The car is still very stiff, and can be made MUCH stiffer with a few clicks or turns of the adjusters. You can't do that with the Bilstein since they are not adjustable.

SWAY/ANTI-ROLL BARS



An excellent upgrade is to fit the 30 mm hollow front bar and 19mm 3 way adjustable rear bay from the 968 M030 package.
Try a Porsche main dealer for prices on these parts These parts will significantly reduce roll Sway bar reduce the amount of lean a vehicle inhibits as it goes around corners. As a vehicle leans (rolls), the center of gravity changes, weight is transferred, and tire contact patch is altered...all adversely affection the handling of the car.

Ideally, for the best suitable setup on a race car, roll is virtually eliminated Sway bars themselves are not the total answer to a better handling car, but they are a start. A nice feature of installing a thicker sway bar versus heavier shocks or springs is that the normal "ride" of the car is not altered (meaning--stiffer/rougher).Most factory installed bars are not adjustable. Some, but not all aftermarket bars are adjustable.

Adjustments can be accomplished by different means, but that is usually determined by the design/manufacturing of the bar. Some bar mounting arms (called drop links) can be shortened or lengthened to set the preload of a bar. The pivot position of some bars can be changed to tighten or loosen the bar.

If you have Weltmeisters on the front of your turbo, they probably have adjustable drop links and a slider arm attached to the bar. Moving the slider towards the end of the bar will in effect loosen the bar, moving the slider in towards the inside will tighten the bar. The same goes for the rear. The drop links can be adjusted to get no preload on the bar when the car sits squarely on all four tires (meaning there is no tension on the bar).

What do the adjustments do? You can change the suspension setup from understeer to neutral to oversteer with bar adjustment. Although there are many other factors to consider that can and should be used to "tune" the suspension, the sway bars are one of the easiest to deal with (either by adjustment or by changing to a larger or smaller size).

Larger is not necessarily better. That depends on other factors. Many times you might adjust the rear bar looser to get a better grip on the front of your car, or vice-versa. One note...if you have the big Weltmeisters, be sure and periodically check your mounts at the front frame rail to be sure that the frame is not cracking.

REBUILDS

In the UK: Koni service

Related Sites www.944s2.com

Supplier links

Paragon

Racers Edge

Speedforce

Lindsey

JRZ

Leda

KONI

Penske

Protrac

Bilstein

Jon Mitchell

This article was prepared with the help of many whose contribution I acknowledge.