Trying to decide on a suspension setup for my SC Targa

[nickelplated5s]

ER sells 'quick change' T bars. If you can wait a few weeks I'll respond about the 900 dollar rabbit hole for my Von's. For your front as a guess, sway bushings. That was my main issue anyway. Front is some poly and some rubber now. I'm going straight rubber when I do the rear.

I've driven Pete's car. His setup is what I recommend as a baseline for what you seem to want. Mines a different sort of kurmudgeon... AKA KarmanS.

[Schulisco]

Originally Posted by david05111

Just imagine, for instance, I shipped the car to Europe and wanted to tackle a 1000 mile road trip, covering highway to Alpine passes like Stelvio and Furka along the way. I want it to be comfortable on the trip, but I want the car to be safe and capable on those passes. And those roads aren't glass. Same idea in the US; the roads aren't going to be perfect, so building the car as though they will be isn't what I'm going for. That's kind of the goal, ultimately.

That's the point - streets here in Europe aren't that flat, neither the autobahn in Germany nor the alps streets. Best highways I remember are in France, but they're not toll free and they're limited to 130km/h - if you go higher, you will run into trouble with the police/gendarmerie and they will charge you with a speed ticket right on the spot...

What i would do:
1. replace the rubber bushings of the rear trailing arms with those from Powerflex
https://www.powerflexusa.com/shop/pfr57-409-porsche-911-1967-1989-rear-trailing-arm-support-plate-bushing-2865?category=1870#attr=947

2. replace the rear shocks with these Bilstein
https://cart.bilsteinus.com/shock-24-001694.html?VehicleType=Car**Truck**SUV**Van&Year=1981&Make=Porsche&Model=911&SubModel=SC
The setting is 1965/1330 which complies with the M474 option when ordering "Bilstein sport suspension" from factory

3. replace the front shock cartridges with these Bilstein (when your car has Bilstein struts)
https://cart.bilsteinus.com/insert-34-050019.html?VehicleType=Car**Truck**SUV**Van&Year=1981&Make=Porsche&Model=911&SubModel=SC
Setting is 1440/1000 which complies with the M474 option when ordering "Bilstein sport suspension" from factory

Keep an eye on proper ride height / ground clearance of the car, esp. here in Germany Police will pull over cars lowered too much. Your car must be able to pass obstacles of 800mm length and 110mm height. If not, they will shut down the car for a complete technical inspection and if necessary to a ride height adjustment...this will cost 100's of bucks.

https://www-autoscout24-de.translate.goog/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp&_x_tr_hist=true

Thomas

[PeteKz]

David, good info on what you want. We can work with that.

First, regardless of what you may have heard on vendors' websites, in magazines, on YouTube, or even in this forum, get this principle firmly embedded in your brain:

Springs (t-bars) do not make a suspension harsh. Shocks have the dominant effect. That might seem counterintuitive to you, but here's why: springs have a linear response to dynamic movement, but normal shocks have a v^2 response to dynamic movement. If you are a mechanical or similar engineer, you can run the differential equations of mass-spring-damper models and see the results in detail, but for discussion purposes, the "linear vs. V^2" relationship is accurate enough.

To qualify those statements a little, I realize that stiffer springs will increase the firmness of the suspension, but one usually installs stiffer shocks along with the stiffer springs. Then, most people think that the springs caused the increase in stiffness and harshness, when it was really the shocks. The stiffer springs will resist compression over bumps more, and resist body roll more, but if you run the same shocks you had before, they won't noticeably increase harshness over potholes, etc. You can prove this to yourself if you install adjustable shocks.

I have to go do some other stuff right now, so cogitate on that explanation and I'll come back later. Or Bill V or someone else will beat me to it.

[Mark Salvetti]

Originally Posted by david05111

My real concern was something like the torsion bars. I can't see myself getting a year down the line, regretting I hadn't tried something different, and having to take that whole spring plate assembly and everything apart on the rear, and the whole front assembly again, and then have it aligned and corner balanced again. I think that whatever I do, leaving it stock or replacing, I don't really want to mess with it again for 10 years. So leaving them stock is fine (I'm sure the bars are in good shape), but I didn't know if going to thicker bars was an obvious thing to do at this point.

Keep in mind that it's not unusual for the front torsion bars to rub after the rubber bushings get old and deformed. If the rubbing is bad enough, you'll want to replace the torsion bars anyway because they can snap where the rubbing occurred. If you bounce the front of the car up and down, does it squeak? Good chance it's the torsion bars rubbing.

I started down the suspension upgrade path when Steve Weiner was still with us. For my 1979 Targa, he recommended 21/27 torsions, Carrera sways, Turbo tie rods, and digressively valved Bilsteins. At the time Steve sold the shocks and they were reasonably priced. I should have bought them, but didn't.

I found the torsion bars and the Carrera sways used on B&S. Instead of the custom-valved Bilsteins from ER (which I think would have been over $2K) I decided to try the adjustable Sport Koni's based on Pete's recommendations (along with others). Got the four from Pelican for less than $900 on sale.

Haven't done anything on the car yet, so am following this thread with interest.

Mark

[PeteKz]

I'm baaaack! Mark, thanks for the caution about torsion bars rubbing due to worn out rubber bushings.

More on torsion bars: the rears of factory 911's have less spring rate at the wheel (proportional to the weight on each end of the car) than the fronts, and that causes the rear to feel sluggish relative to the front. I'm sure that Porsche specified it that way for a good reason, but they had to compromise a number of parameters for street cars to appeal to a variety of buyers and markets.

Pretty much everyone here and in the performance world installs stiffer t-bars. The "standard" recommendation, at least since Bruce Anderson started writing about setting up 911 suspensions 40+ years ago, is 21mm front and 27mm rear. Some prefer 20 front and 26 or 27 rear, but the take-away is pretty clear--911's do not have stiff enough t-bars for spirited street driving for most of us. Note that the 21 front (up 2 mm from 19)/27 rear (up 3mm from 24) combo increases the spring rate at the rear more than the front, thus balancing the front to rear feel.

NOTE: I currently have 26mm bars (out of a 930) in the rear of my car, because that's what I started with years ago. I bought some 27 rear bars because I still felt like the rear was "lagging" the front, and it lifts the inside front wheel during autocross turns, but I haven't got around to installing them yet.

Your car weighs about 200 lbs more than my car, so I echo Bruce Anderson's books and recommend that you go with 21/27 bars.

Next questions for you: Do you have Bilstien or Boge front struts? You can identify them by looking at the strut. Bilsteins are usually painted green, and Boges are usually painted black. Jack up the front of the car and look closely at the stampings on the strut. If it's Boge, it is stamped on the strut (I don't know whether all the Bilstein struts are stamped). IN addition, the Bilstein struts have two pins at the bottom of the strut. The lower and larger one holds the strut onto the ball joint. The smaller one above it is a roll pin that goes through the strut from one side to the other. The Boges only have the one pin for the ball joint.

Next item: bushings. With the car on the ground, take a picture of the spring plate cover. We want to see if the t-bar cover is pushed up against the spring plate cover.

[david05111]

Originally Posted by PeteKz

I'm baaaack! Mark, thanks for the caution about torsion bars rubbing due to worn out rubber bushings.

More on torsion bars: the rears of factory 911's have less spring rate at the wheel (proportional to the weight on each end of the car) than the fronts, and that causes the rear to feel sluggish relative to the front. I'm sure that Porsche specified it that way for a good reason, but they had to compromise a number of parameters for street cars to appeal to a variety of buyers and markets.

Pretty much everyone here and in the performance world installs stiffer t-bars. The "standard" recommendation, at least since Bruce Anderson started writing about setting up 911 suspensions 40+ years ago, is 21mm front and 27mm rear. Some prefer 20 front and 26 or 27 rear, but the take-away is pretty clear--911's do not have stiff enough t-bars for spirited street driving for most of us. Note that the 21 front (up 2 mm from 19)/27 rear (up 3mm from 24) combo increases the spring rate at the rear more than the front, thus balancing the front to rear feel.

NOTE: I currently have 26mm bars (out of a 930) in the rear of my car, because that's what I started with years ago. I bought some 27 rear bars because I still felt like the rear was "lagging" the front, and it lifts the inside front wheel during autocross turns, but I haven't got around to installing them yet.

Your car weighs about 200 lbs more than my car, so I echo Bruce Anderson's books and recommend that you go with 21/27 bars.

Next questions for you: Do you have Bilstien or Boge front struts? You can identify them by looking at the strut. Bilsteins are usually painted green, and Boges are usually painted black. Jack up the front of the car and look closely at the stampings on the strut. If it's Boge, it is stamped on the strut (I don't know whether all the Bilstein struts are stamped). IN addition, the Bilstein struts have two pins at the bottom of the strut. The lower and larger one holds the strut onto the ball joint. The smaller one above it is a roll pin that goes through the strut from one side to the other. The Boges only have the one pin for the ball joint.

Next item: bushings. With the car on the ground, take a picture of the spring plate cover. We want to see if the t-bar cover is pushed up against the spring plate cover.

I'll get those pics for you tomorrow. I think they're Boge struts. I don't see a hint of green, but I'll look again tomorrow for sure

[Bill Verburg]

Here's comparison of various t-bar suspensions on a '76 Carrera 3.0, very similar to an SC except for engine, wheels and tires, this comp uses Bilstein shocks Boge will knock ~12% off these ride frequency #s


The ride frequency is one of the better metrics to describe how a car feels
top row is stock SC
the lower the more more comfortable
the closer the front and rear are the better the ride comfort,
the bigger the front relative to the back the more understeer and vice versa

roll control for sporting street use wants to be in the 800+front range and 750+rear range, but does depend on wheels, tires and driver aggressiveness

the higher the spring rates the less mechanical grip, countered by better utilization of existing grip

[david05111]

I have confirmed they are Boge struts. Pictures of that, plus those of the spring plate covers requested are below.

[ccallana]

my plates looked similar - bushing squished so far that the frame and the plate are touching... new bushings would be good here

[Cherry Bomb]

Don't under estimate the capabilities of Targas and Cabrios!

I've out run many late model variants as well as other makes, in my prepped Cabriolet.

[Schulisco]

As you have Boge struts make sure that you get the right cartridges, if you want to go with Bilsteins in the front:
First of all check whether you need them for inner or outer thread of the strut, then chosse the cartridge:
https://cart.bilsteinus.com/insert-34-001141.html?VehicleType=Car**Truck**SUV**Van&Year=1981&Make=Porsche&Model=911&SubModel=SC
https://cart.bilsteinus.com/insert-34-001134.html?VehicleType=Car**Truck**SUV**Van&Year=1981&Make=Porsche&Model=911&SubModel=SC

Both are series replacements, no sport road or race setup. As I mentioned earlier it's no recommended to go stiffer than original M474 on a Targa or cabriolet.

[Cherry Bomb]

83 911SC Cabriolet
21/27 Hollow TBs
Eibach adjustable sways @ middle setting
19mm raised spindles with Green HDs
Was Green HDs rear, now Yellow Street Sports
All ER Sport Rubber throughout currently. (Springplate bushings failed early on) Going Rennline Billet/Delrin
18x8 225/40/18 & 18x9.5 255/35/18 Conti ECPlus 02

Aligned aggressive street, corner balanced and 2450# with 1/2 tank.

The ride is compliant and enjoyable as listed. Typical drive time is 5-7hrs each outing, never exhausting no matter how spirited the trip gets.

I'm figuring after Rennline delrin bushings are installed, the ride will be smoother.

Total point and shoot Hot Rod that's been stamped "Approved" by my boss. ;-)

[PeteKz]

Agree with the others: the rear bushings need to be replaced. If the rears are shot, so are the fronts. However, on the front A-arms, the forward set of bushings bear significantly less weight than the rear ones, which carry the weight of the car. You can replace only the rear set if the fronts are not squished.

You will be using rubber bushings, so here's some info about rubber parts. Material quality is critical. You can't tell by looking at them, the quality can only be known after years in service. The original parts lasted 25 years or more, and Wayne Dempsey, Bruce Anderson and others have noted that the OE bushings were the highest quality available. You may have noticed that window seals, rubber trim, and other original rubber parts last a long time, but the aftermarket stuff usually get stiff, dries out and cracks in a few years. High quality rubber parts have a high amount of natural rubber in the formula, but that's more expensive than the synthetic rubber components, so manufacturers have a financial incentive to reduce the natural rubber proportion. Be careful of anything made in China, as the contract manufacturers there are notorious for starting out making a part to the specification, but if the buyer does not carefully monitor the process, the manufacturer will cheapen the material, loosen the tolerances, and take other shortcuts. About the only thing you can do as a customer is to buy from a seller who has a reputation for quality and will replace poor quality parts. But even so, I've bought parts from NAPA that were the same part (made in China), but several years apart, and the later ones were poorer quality.

Some people have replaced rubber bushings with supposedly OE equivalent, and they ended up being squished in a few years. Some have reported good long-term results with the standard rubber Elephant Racing bushings. In your discussions with vendors, specifically ask which bushings will last the longest and buy those. Given the crap available in the aftermarket, I would strongly consider the OE Porsche bushings, even with the "Porsche tax," to get parts that will last a long time.

You can send the rear arms and front A-arms to Elephant to have new bushings installed, or you can buy tools to do it yourself. The spring plate bushings must be replaced on the car and are a DIY job. See Wayne's book, "101 Projects for your 911," for detailed instructions.

Speaking of spring plates: Get adjustable spring plates if you don't have them already. I prefer the screw-adjustable ones instead of the Porsche Carrera style eccentric adjusters, They are easier to adjust and get the same change on both sides. Several vendors sell spring plates with the bushings vulcanized to them. You might consider those if they have a good reputation.

[PeteKz]

Shocks: For street cars, I like the Koni Sports (yellow) best. The great advantage of these is that they are externally adjustable with a knob on the top of each shock. The Koni Classic (Red) shocks are also adjustable, BUT you have to remove one end from the car in order to adjust them. I have the Koni Sports on my car, and it is literally a 5-min job to go around the car and change the adjustments. This makes it easy to increase the damping for AX or track days, and then soften them up for the drive home. Since the roads around my house are fairly rough, I set them at the softest setting for street use.

These are what you want: https://www.pelicanparts.com/More_Info/KON86411039SPORT.htm?pn=KON-8641-1039SPORT&SVSVSI=568&DID=244366
https://www.pelicanparts.com/More_Info/KON82101159SPORT.htm?pn=KON-8210-1159SPORT&SVSVSI=568&DID=244367

IMO, Bilsteins are too harsh for most street cars, especially the Sport versions. Especially on average roads. The Bilsteins are not adjustable, so if you think they are a bit harsh for your roads, you can't change that. I know many people here like them, so see if you can find someone in your local club with Bilsteins who will let you drive their car. Then, don't just drive it around the block, take it for a long drive at highway speed on highways that aren't perfect; because that's where you do the great majority of driving.
Also see this video from Garage Time:
https://www.youtube.com/watch?v=JzSzoESEhCQ

Sway bars: Lots of good choices here. I strongly prefer those that are adjustable because that allows me to tune the roll stiffness and oversteer/understeer characteristics. Stiffer sway bars do increase ride harshness. The sway bar transfers some of the force of hitting bumps and potholes to the other side of the car, and through the sway bar bushings to the chassis, which are usually stiff polyurethane. FYI, I still have the stock 1973 sway bars in my car. After increasing the t-bars, my car is well balanced as-is, so I don't feel a need to install stiffer sway bars. Yet.

Tie rods: Chances are good that the original tierods are still good. Check for looseness including at the rubber bushing close to the steering rack. Check the the rubber boots over the ball ends are not split or torn. Do not change to turbo tie rods until after you have done all the other suspension work and driven the car for awhile.

Ball joints: Only replace on condition. If no play and the rubber boots are good, leave them alone. FYI, I'm still on the original ball joints after 52 years and 135,000 miles.

Ride height: Set the car to the "RoW" ride height specs, if it isn't there already. Use the specs in the shop manual or as posted on other threads on this forum. Do not go lower than these specs unless you decide to change the front struts to "raised spindles." If you like the appearance of the car at the standard ride height, then keep it there and you won't have to spend at least another $1000 (but probably closer to $2000) to raise the spindles. If you still want it lower, then raised spindles will lower the front about 3/4" (19mm) and give the car a more aggressive nose-down stance. As for improving the handling, I doubt you will be able to tell any difference on the street. And you shouldn't do that kind of driving on public roads.

Tires: Tires make a huge difference in handling, not to mention comfort, cabin noise, and safety. Lots of good choices here too. First decide how you will use the car. You already said it would be primarily a street car and needs to maintain comfort and be wife-friendly, but do you expect to only drive it on nice days, or will it need to serve you in a wider range of weather conditions? Choose tires accordingly, or do what I did and buy an extra set of wheels and mount winter tires for the seasons when the roads are mostly wet and slick.

[PeteKz]

How to approach your project:

1. Keep it a "driving project." I always advise to keep your car a driving project as much as possible. That means to break your overall project into tasks that can be accomplished in a weekend or a few, and drive the car in-between those as much as you can. Count on each project taking longer than you planned. Count on having to order something mid-job that you didn't order the first time. If you try to do them all at once, the delays pile up and it becomes a "garage project" rather than a driving project. Take a look around this forum to see what I mean. Several guys have had cars in their shops for 20 years or more, still not driving. When a car sits that long, moisture, corrosion, leaking seals, frozen brakes, etc. happen. Then the project gets even longer. Then you frequently end up saying to yourself that you'll get to it "someday", and then you end up in a retirement home and your kids have a project that was sitting for 25 years. So keep it drivable as much as you can, and enjoy driving it in between your tasks. If you have experience at these types of projects, and you think you can do it all at once, then you know what you're getting into.

2. Make one change at a time. That's good general advice, but on suspensions, you want to make a change and see how it affects the car, before you make another change. Otherwise, you can end up chasing your tail and getting frustrated as you try to sort out handling problems.

Order of tasks:
Do the rear end first, then the front. Drive the car in between tasks.
1. Change the spring plate bushings, spring plates if you bought new ones, control arm bushings, and t-bars. Yeah that doesn't follow the "one thing at a time" rule, but it will take a lot longer and multiple assemblies/disassemblies to change them separately.
2. Align the rear suspension and corner balance the car.
3. Change the rear shocks after you have driven the car with the new t-bars and bushings installed. Get used to the first set of changes, then change the shocks, then experiment with the shock adjustments.
4. Change the front A-arm bushings and reinstall the A-arms. Set front ride height and align the front suspension. Drive the car for awhile and see how that changes the feel of the car. Change the ball joints or tie rods only if they are worn.
5. Change the front t-bars (they slip in and out of the A-arms from under the car, so you can change them without disassembling the A-arms). Recheck the corner balance and ride height. Then drive the car again and see how that changes the handling and feel.
6. Change the front shocks. If you plan to install struts with raised spindles, do that too.
7. Check and adjust the front suspension alignment and ride height and recheck corner balance.
8. Drive the car hard over a variety of roads. Adjust the shocks to your preferences.
9. Take wife/girlfriend/mistress/significant other for a drive!

[Funracer]

Want to thank the OP for this timely thread, as well as all the great info from PeteKz, Bill V et al. This is my next project on the 83SC!

[HarryD]

As a data point:

My 1973.5 with 184,000 miles has a mostly stock suspension. The upgrades were done years ago. I drive on the street for fun, autocross 5-8 times, and about 6 HPDE's a year.

My suspension has turbo torsion bars (21 mm front/26 mm rear).
Front and rear 19 mm adjustable sway bars.
I replaced my rear spring plates bushes with Neatrix parts. All other bushes are stock and original.
Bilstein HD fronts and Sport rears.
Weltmeister front Strut Brace
Turbo Tie Rods
The Car has been lowered and corner balanced by a very good local shop.

My front suspension bushings are original and my shop has not indicated I need to replace them.

Everyone who has driven my car (both at HPDE and street) reports the cars handles well. Petekz on this thread is one of the drivers.

[shoooo32]

Man what a great thread! This one deserves a sticky.

I agree with the heavy hitters in the room. Lots of solid advice on how to build a nice, sporty aircooled 911 without compromising comfort. To that point I must point out that a lowered 911 with stock spindle height will be riding on the bump stops most of the time. If you want to be lower than "euro ride height", raised spindles and Koni 1159 rear shocks (or similar shorter body) are a must in my opinion.

My current setup (1978 Targa): 21/27 torsion bars, RSR control arm and swing plate bushings, Tarett sway bars, 19mm raised KW V3s, "sport rubber" rear control arm bushings and strut mounts, turbo tie rods and Tarett adjustable bump steer kit, 7&9x16 Fuchs w/300tw tires. I didn't start here - my first attempt was new Bilsteins, then bigger T bars, then eibach sways, then Koni 1159s... everything fixed one problem and made a new one. Slippery slope and all...

[Bill Verburg]

Originally Posted by shoooo32

Man what a great thread! This one deserves a sticky.

I agree with the heavy hitters in the room. Lots of solid advice on how to build a nice, sporty aircooled 911 without compromising comfort. To that point I must point out that a lowered 911 with stock spindle height will be riding on the bump stops most of the time. If you want to be lower than "euro ride height", raised spindles and Koni 1159 rear shocks (or similar shorter body) are a must in my opinion.

My current setup (1978 Targa): 21/27 torsion bars, RSR control arm and swing plate bushings, Tarett sway bars, 19mm raised KW V3s, "sport rubber" rear control arm bushings and strut mounts, turbo tie rods and Tarett adjustable bump steer kit, 7&9x16 Fuchs w/300tw tires. I didn't start here - my first attempt was new Bilsteins, then bigger T bars, then eibach sways, then Koni 1159s... everything fixed one problem and made a new one. Slippery slope and all...

Here's a survey of what is needed to maintain stock geometries on a lowered 911


and a survey of factory setups

[PeteKz]

Originally Posted by HarryD

As a data point:

My 1973.5 with 184,000 miles has a mostly stock suspension. The upgrades were done years ago. I drive on the street for fun, autocross 5-8 times, and about 6 HPDE's a year.

My suspension has turbo torsion bars (21 mm front/26 mm rear).
Front and rear 19 mm adjustable sway bars.
I replaced my rear spring plates bushes with Neatrix parts. All other bushes are stock and original.
Bilstein HD fronts and Sport rears.
Weltmeister front Strut Brace
Turbo Tie Rods
The Car has been lowered and corner balanced by a very good local shop.

My front suspension bushings are original and my shop has not indicated I need to replace them.

Everyone who has driven my car (both at HPDE and street) reports the cars handles well. Petekz on this thread is one of the drivers.

Yes, I have driven Harry D's car and it handles very well and does not beat you. I was somewhat surprised it has Bilsteins, as the ride was softer than I have felt in other cars w Bilsteins. I've only driven it short distances (a few miles on one occasion, and on the AX track), so I can't vouch for long distance comfort.