First time post here. I've been looking into upgrading the suspension of my 1984 944. This car is my daily driver but I'd also like some better handling out of it and stiffer suspension. I've decided to do a rear seat delete and I plan on getting upgraded Koni struts with coilovers in the front with upgraded rear Koni struts and new rubber bushings all around. What would be a good front spring rate and torsion bare size? Should I also change the rear springs to ensure even ride height. I'll do the sway bars later on if necessary. Not really bringing it onto the track so I'm leaning more towards a neutral/understeer suspension. I'm still a pretty novice mechanic so I plan on having someone else install the torsion bar and help with the alignments.

 

The torsion bar are the rear spring. You will need to re-index the torsions in order to adjust the rear height, which is not the easiest of jobs (requires dropping the rear suspension), but if you do your research, take your time and understand how many degrees each inner/outer torsion spline will move, you can calculate the drop beforehand and do it correctly the first time. I would be sure the shop thats doing the install is familiar/confident on dialing in rear torsion bar suspensions found on the older VW/Porsche's.

I would recommend this kit from Paragon. Its going to give you Koni yellows on all 4 corners, front coil overs and an upgraded, stiffer rear torsion bar to match the stiffer front springs.
https://www.paragon-products.com/Kon.../944spec-1.htm

Spring rates are subjective and often debated. In my opinion good street setup would be something like 250 lb front springs with a 27 or 28 mm torsion bar (220/250 lbs respectively)

 

Hi Zudi944,
The biggest mistake regarding suspension upgrades is to stiffen the front spring/bar package without making a similar increase to the rear torsion bar/sway bar package. You need to keep the roll stiffness of the front and the rear in sync or you will just introduce handling problems. If you want a really simple answer, I agree with @walfreyydo that the Paragon 944spec suspension package has been selected by the 944spec racers to give a much stiffer suspension but balanced front to rear. I had it on my track car. I also agree with him that it is probably too stiff for regular street use, especially if the roads where you live in NY are as rough as I suspect they are. Call Jason at Paragon-Products and he can probably suggest a "944spec lite" package that uses 250# springs on the front and a commensurate increase in the rear torsion bar size. As I recall the 944spec package uses 350# front and a 30mm rear bar. As he will tell you if you ask, the package is limited by the shocks so if you go less stiff you should be fine.

You might want to read Clarks-Garage. He has several recommendations for balanced suspension upgrades. Most follow the example of what Porsche did for the 944Turbo.

And you are absolutely correct to replace all the rubber bushings first. I know it seems crazy but just doing this alone will transform the handling of your car.

There are several articles on my website about suspension for early 944s.

 

Thanks for the advice walfreyydo . I just assumed that the rear had springs instead along with the torsion bar. I was planning on getting that kit with the same spring rate and 27mm torsion bar. I suspect the suspension will also be stiffer with the weight reduction as well. I'll keep up with my research

 

According to Clarks, it' seems that 200# seems like a good spring rate paired with a 26mm torsion bar. I think that going up to 250# paired up with the weight reduction might be too stiff on the NY roads like you said. So what I'm starting to understand is that the torsion bar must be the right size so the rear spring action matches with the front springs/ coilovers. Would a 27mm torsion bar with 200# springs be pushing it too far with the torsion bar size? I head this could cause more oversteer.

 

The nice thing with running front coil overs is that you can change out those front springs to fine tune the ride and handling. Although the rear torsions will be static in terms of spring rates, if the car is understeering or oversteering too much you can make the front springs stiffer/softer to tune some of that out. Front rear swaybar size changes can also help with that.

+1 for Jason at Paragon. You can give him a call and he can recommend a good front spring rate/rear torsion size pairing based on your needs.

For the 944 spec package I linked, there is options to select the front spring/rear torsion combo you desire, so they are not locked in at #350 (probably was prior to the website update)

 

It gets complicated in a hurry. First, the front and rear "roll resistance rate" is a combination of the springs and the sway bar. In the front you have a coil spring and a standard sway bar. In the rear you have a linear spring (the torsion bar) and a sway bar. I have a complicated spread sheet that does the math but if is based on ideal conditions. If you want to keep it simple, if you go with 250# (actually pounds per inch but everyone shorthands to pounds) then in Clarks Garage there is a conversion chart for the rear torsion bar that says a 28mm rear torsion bar has a spring rate of 254# Close enough to keep you balanced if you keep your existing front and rear sway bars.
Note the 250# springs typically lower the front of the car. This is OK except you need to, as Walfrey said, re-index the rear torsion bar to also lower the car the same amount. If you replace the bar with the bigger one, you will be in there anyway.

 

Getting on my soapbox for a minute, body roll is not the enemy of handling, at least not on an 80's car. It is the enemy of aero induced grip and since on race cars aero is very important, suspension compliance is sacrificed to avoid upsetting the aero profile of the car. As a matter of fact, Formula One drivers in the early days of aero design were very upset that their cars no longer rolled and they lost the ability to predict how the car was approaching the limit. It's all in the muscle memory you have built up. Anyway, if it were me for your vintage car, my priorities would be high performance tires (in the summer), get all the 30+ year old rubber bushings in the suspension replaced, and then embark on weight reduction. That would include in fitting a set of Fuchs wheels if you can find them. For street driving on any kind of rough roads, leave the spring rates alone until you really think this is holding you back. Remember, it is more fun to drive a slow car fast than a fast car slow. Especially with your winter tires on a snowy road!!!

 

One more factoid. The early 944 suspension design does a very good job of absorbing largish suspension movements without the camber profile of the tire getting way out of whack. Tires work best when their tread is parallel to the road surface and the 944 suspension design does a very good job of making sure this happens. Even with significant body roll. Here are a couple of articles I did on this subject.

https://newhillgarage.com/2012/06/11...ension-camber/

https://newhillgarage.com/2017/01/06...camber-values/

Again, don't sell short the engineering done by Porsche on the 944. You might find it harder than you think to make improvements.

 

That sounds like a great idea especially since this is the first car I've actually decided to do some work on. All focus on getting the old suspension up to standards. Thanks Harvey

 

If you are interested in having a good handling car, body roll is a considered factor. Defining body roll around the c of g. There is a sweet spot between equivalent spring rates and anti roll or sway bars. Heavier front spring rates transfer weight to the front faster than softer spring rate and stiffer front sway bar. Also if your race car double adjustable compression and rebound adjustments can also add to the mix. It is a complex interaction mixed with driving style.

On my 1983 Porsche 944 race car, my front suspension is HighStrung LCA with spherical bearings, 400 lb/in front springs, and MO30 25.5 mm sway bar with delrin mounting bushings, rubber mounted sway bar link to delrin/rubber connection to LCA. So the front suspension is very rigid but not 100 %. The rear is 31 mm hollow torsion bars, all rigid connectors points, 19 mm sway bar with rigid mounts set a full hard.

The bottom line is the race car rotates, pointing in the right orientation from apex to corner exit. The car does not understeer, is neutral, and if aggressive with the throttle does oversteer.

The first key as Harvey stated is to match effective spring rate of front with effective spring rate or rear. Then the sway bars are influenced by how rigid or flexible the front and rear suspension pick up points are. Fine tuning is with double adjustable shocks matched to effective spring rates. Koni is not the shocks. The best cost effective shocks are ANZE, uses Penske Shocks components at half the price.

Then you drive to adjust suspension or hire a professional race driver to do check out.

 

daily driver - no more than 200# front springs and 26 or maybe 27mm torsion bars out back. for typical roads you'd find in the US anything more will be uncomfortable.
if it were a weekend toy like mine you could stand to go stiffer but not a lot of point on the street.

i have 200#/26mm and the car is neutral with maybe a little oversteer tendency. i have 25.5mm/18mm sway bars on my car, car is about stock height (used a spring spacer on the front). i put new Boge/Sachs shocks/struts all around and they seem to do fine with controlling the stiffer-than-stock springs. all bushings were replaced when doing the shocks/torsion bar service in 2014.

for a street car no need to spend big money on shocks/struts. as harvey said, good tires, fresh bushings and replace the shocks if yours are old and you'll be well ahead.