1978 911 SC Suspension/Shock Refresh

[charlesgrant91]

As it sits now, it looks like I am targeting a setup similar to @PopsRacer.

Stock TBs
Turbo tie rods
Bilstein HD green in front
Bilstein Sport yellow in rear
Prekom sport rubber bushing for lower control arms, spring plate, and rear trailing arms. Saves about $200
when compared to ER bushings. Thanks @Ltanderso for the rec.
Standard rubber for sway bars, strut mounts, etc.
Possible upgrade or late Carrera or similar sway bars.

I am already running 7s in front and 8s in rear with summer tires so I have that covered.

I feel like this should be a pretty good street setup without being overly stiff and without breaking the bank.

I appreciate all the knowledge shared in this thread. It has been very helpful.

[icarp]

This is from another post regarding shocks

Often the Bilstein "sporty road" setting is recommended by people as a replacement or performance upgrade. But the stiffness of them on the rear is almost doubled than the factory (standard) sport shocks from Bilstein...so with the "sporty road" the car get's much harder und way more uncomfortable! Do you know what kind of dampers the car currently has?


The settings number pattern is rebound/compression. You can see on this list that esp. the rear "sport street" damper is almost twice as stiff as standard version. The sport street setting is the stiffest on the market from Bilstein! For me this is very uncomfortable! Before ordering best you test drive such an equipped car.

Thomas


I think based on your goals and for your driving preferences you have chosen a very stiff ride.
I run the adjustable koni reds and sport yellows on the cars I tune .
for the yellow the front is turned in about 2.5 hours from full soft frnt an full soft in the rear ,
The reds get 12 hrs and 3-4 more hrs, I want the softest ride for the street and good control and predictability for the canyons . Stock suspension from porsche is fantastic, a good alignment and a softer compression shock are the keys to a car that is comfortable and fun to drive
Any of my cars can keep up with any hot rod stiff super all the right high $ crap bought just to ruin the ride .

Just my thoughts
Ian

[charlesgrant91]

@icarp

Thanks for the info. I’ve really been riding the fence on the Bilstein yellows in the rear. Might just go with the HDs all around in that case. I can get a good price on the Bilstein from our parts supplier but they don’t have any deals on Konis or anything else really except KYB or maybe a Sachs. I am currently running some sort of Boge yellow in the rear. Not sure if it’s stock or not. Also not sure what’s in the front. The car has over 260k miles and has not had a full suspension refresh from what I can tell so it is well past due.

[PeteKz]

Charles, Listen to Ian. If you still want to ignore his advice about Koni's for the street, then get the softest Bilsteins. DO NOT get the stiffer Bilsteins. Watch this:

https://www.youtube.com/watch?v=JzSzoESEhCQ

And I'll beat the horse again: Stiff shocks compromise the ride far more than stiffer T-bars. In addition, stiffer T-bars (or springs) reduce roll in cornering, but stiffer shocks do not. If anything, you should approach this the other way: Increase T-bars to 20/26 or 21/27. Then change the shocks. You can look up my many other responses here that explain why.

[Schulisco]

Appreciate and feel honored to be quoted by Ian :-)

There were several discussions on this topic recently, you'll find a lot of information there.

http://forums.pelicanparts.com/porsche-911-technical-forum/1146144-shocks-recommendation.html

http://forums.pelicanparts.com/porsche-911-technical-forum/1111488-bilstein-shock-question.html

http://forums.pelicanparts.com/porsche-911-technical-forum/1161343-rear-shocks.html

Additional note: I heard a quote these days that the Kayaba shocks are as soft as the Woodhead shocks Porsche used earlier mainly on US models. So they're pretty much softer than Bilsteins and also as the original Boge/Sachs shocks.

Thomas

[icarp]

This is one of the best descriptions of the evolution of the "performance shocks" .
Note that the digressive shock was developed for racing cars !!! not street cars !!
The shock was then redeveloped into the regressive a much better all around shock.
Most of us can't afford the 5 way multi adjustable shock , they are amazing .

Read and have fun , 911 suspension 1965-1989 really the same set up the whole run.
Either just an oil shock or a very low pressure gas shock, ie, "koni yellow external adjustment"
Send me your number and I can help you get the right Koni's for your car


https://www.penskeshocks.com/blog/linear-progressive-regressive-digressive-shock-valving-differences-and-use-cases

[Cobalt964ruf]

interesting read

[Schulisco]

This table I created from the data out of the Bilstein classic catalogue with all known suspension / shocks setups for the 911:

Columns: Setup name, front axle, rear axle. The numbers are rebound/compression in Newton.
"Sportlich Strasse" means sporty road and is the stiffest/hardest suspension for these cars and not recommended for non trackday drivers. And on Targas/convertibles it should be forbidden as the body suffers too much on that.



Thomas

[Marko888]

Charlesgrant91,

I’ve been through this a couple times with my Carrera.

Bilstein HD’s front and rear on stock torsion bars was a nice setup for a street car. Sporty, but not harsh.

Search for Bill V’s many posts on ride quality…likely no need for bigger torsion bars.
We’re mostly amateurs posting here, but all but one of the pro’s I talked to were less keen on bigger torsion bars for a street car.

I do agree that shocks are more significant.

It’s very rewarding to refresh suspension on these cars. Enjoy!

[Bill Verburg]

Originally Posted by Schulisco

This table I created from the data out of the Bilstein classic catalogue with all known suspension / shocks setups for the 911:

Columns: Setup name, front axle, rear axle. The numbers are rebound/compression in Newton.
"Sportlich Strasse" means sporty road and is the stiffest/hardest suspension for these cars and not recommended for non trackday drivers. And on Targas/convertibles it should be forbidden as the body suffers too much on that.



Thomas

you gotta realize that a shocks behavior can't be defined by a single # pulled from a catalog

those #s are all off by a factor of 10

those #s only apply to a specific rod speed of .54 m/s, which is quite fast

when the catalog says at what will be measured by a consumer are usually at odds

here's a Rohrig shock dyno graph of the performance of Bilstein hd (green), Sport(yellow), and a custom digressive revalve of either.
Not that even this chart does not fully describe the behaviors of the shocks as the gas pressure component has been zeroed out of all of them.




what you learn from the chart is that stock hd &sport are linearly valved which means that the damping increases w/o bound, this run goes to a shaft speed of 10 in/s which is a bit less than 1/2 the Bilstein factory spec. and yes this is a factor contributing to discomfort, it would be much nicer if a high speed blow off was used as is done by Ohlins

the reason digressives are so much nicer is that the damping force levels taper off at high speeds plus of course the additional damping at low speeds which is where vehicle maneuver speeds are generated

back to gas pressure effects, stock Bilstein have a static force of ~42#s extending the damping rod, when not zeroed out for a computer display, this raises all the reactive damping force so that it oscillates around that static #, for instance here if the dyno was measuring the oscillations @4 in/sec the forces would be in the range from ~60# to ~20#s, and would cause additional friction in the motion, all this internal hysteresis leads to delay in reaction time. The gas pressure introduces a position dependent variable into a velocity dependent design

a non inverted monotube would be worse in this respect as they use damping rods that are larger larger which cause greater rod forces( Force = pressure *area) despite this drawback the monotube is generally considered to be superior to the twin tube design for performance use.

the twin tube on the other hand is general considered to deliver a more comfy ride using damping ratios that are ~.3 to .6 where for performance applications you want d/r ~.6 to ~1

the shock cannot be considered in isolation as it is only 1 component of the suspension system


1) the tire spring rate
2) the tire damping rate
3) the suspension spring rate
4)the suspension damping rate
5) the force on the road
6) the force on the sprung chassis weight
Mu is unsprung mass
Ms is sprung mass

and the front performance is not unconnected to the rear

ride frequencies are a very good measure of ride comfort
for comfort the rear r/f wants to be a bit higher than the front r/f, this imparts what is called a flat ride, but it is also slower to react than the opposite where front r/f > rear r/f which leads to pitching, most race cars will have this characteristic because performance is the goal not comfort. This also applies to tires where taller sidewalls are more comfortable than shorter, but if performance is the goal o short side walls are more desirable

sorry for the long winded digression I just got an a roll w/ nothing else to do on a cold windy day

[Cherry Bomb]

FWIW, I just replaced low mileage, rear Green HD with Yellow Street Sport. Absolute improvement over HDs for my set up! Car feels balanced at last! Should've done it sooner. I have mostly ER Street/Sport package with Eibach sways and now Yellows completing the system.


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

[Bill Verburg]

Originally Posted by Cherry Bomb

FWIW, I just replaced low mileage, rear Green HD with Yellow Street Sport. Absolute improvement over HDs for my set up! Car feels balanced at last! Should've done it sooner. I have mostly ER Street/Sport package with Eibach sways and now Yellows completing the system.


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

sort of surprised to see that set up on a Cab, its extremely racy, ride freqs. 2.596/2.428 are well into the moderate downforce race car territory and nicely paired, love the wheel & tire set ups very, very grippy and efficiently uses limited 3.0 engine torque, roll stiffness is quite high too, it's going to be very flat in the twisties.

definitely a performance as opposed to a comfort set up

[Schulisco]

Originally Posted by Bill Verburg

you gotta realize that a shocks behavior can't be defined by a single # pulled from a catalog

those #s are all off by a factor of 10

those #s only apply to a specific rod speed of .54 m/s, which is quite fast

when the catalog says at what will be measured by a consumer are usually at odds

Thanks for pointing out the factor I missed. I didn't knew that these numbers are measured on a pretty fast speed. This explains also why I feel the sport road shocks feel slmuch harder while rolling over bumps and potholes...
And thanks for the quick lesson on ride dynamics! Appreciate it.

Thomas

[Cherry Bomb]

Originally Posted by Bill Verburg

sort of surprised to see that set up on a Cab, its extremely racy, ride freqs. 2.596/2.428 are well into the moderate downforce race car territory and nicely paired, love the wheel & tire set ups very, very grippy and efficiently uses limited 3.0 engine torque, roll stiffness is quite high too, it's going to be very flat in the twisties.

definitely a performance as opposed to a comfort set up

Thank you! Your assessment means a lot to me.

Truth be told, I wasn't planning to go this far with a soft shell 911. I'm very happy with its abilities and eager performance on and off the track. (Limited track time) Absolutely confidence inspiring going into turns with gentle mid turn adjustment feedback.

Aligned aggressive street, corner balanced and #2450 1/2 tank. Weight loss from rear and center/interior only. All steel with bumpers. Power delivered by fresh crank out 86' 3.2 with Fabspeed RSR headers muffler system, Patrick LWFlyW, web20/21, SW bigger TB & custom 93oct chip. 915 also fresh with CMS sidecover, OS Giken LSD (safest mod to date) etc etc! My favorite additions are Pole Position ABE seats and C.A.E. shifter/370mm Prototipo pairing!

[Mr. Merk]

Originally Posted by PeteKz

Charles, Listen to Ian. If you still want to ignore his advice about Koni's for the street, then get the softest Bilsteins. DO NOT get the stiffer Bilsteins. Watch this:

https://www.youtube.com/watch?v=JzSzoESEhCQ

I have Konis on my 1950lb 912 and they feel great.

I have the green/yellow Bilstein combination on my 2700lb G50 Carrera and they feel great. Very compliant. My car sails over rough roads without a thought while my friends in the newer water pumpers are rattling their teeth out and go much slower.

The 68 912 had lighter bars than any other year or model while the G50 had the stiffest (other than Turbo.) I don't ever plan on increasing torsion bar size on either of my cars.

[charlesgrant91]

Thanks all. After speaking with Ian at length, I am planning on going the Koni route along with stock T-bars and rubber. I think it will be the best setup for my driving needs at this point in time.

[PeteKz]

Good decision. You will have the advantage of adjusting the shocks to your preferences, and to see how those changes affect ride and handling. Let me beat this point again: Get the Koni Sports (Yellow) instead of Classics (red). They cost only a little more than the Classics, and are far easier to adjust with a knob at the top of the shock. At their softest setting, they are only a little stiffer than the Classics at their softest setting. On your SC, you probably will want to increase to the 2nd click anyway. In my 1973 car I run them at the lowest setting on the street, and at the 2nd click on AX. .

[Cherry Bomb]

It'll ride like butter and handle just right! Tire choice will be the gap between touring and playing. Sensible build.

Enjoy the ride!

[DennisMenace]

Hi everyone. I am planning to replace all rubber bushings on my car with Prekom bushings. Any recommendation whether to go with OE hardness (65 shore) or sport (85 shore) for the following parts?

- Control arm front
- Strut mount front
- Trailing arm rear
- Sprint plate mounts

Planning to use the car for canyon / mountain driving, but also some longer distances. Car will run on 21/27 mm torsion bar, stock sway bars, KW V3 with raised spindles.

Best
Dennis

[charlesgrant91]

After it was all said and done, I ended up using Prekom bushings for the front control arms, rear trailing arms, and spring plate bushings. I went with sport hardness wherever it was available. I used Lemforder stock-style replacement for the front strut. My housings appeared to be slightly deformed, so I just went with new ones.

I am very happy with ride quality and overall performance. Definite improvement from the hard and sagging stock bushings. I frequently drive the car around an hour each way to and from work (twisty backroads) and have no complaints regarding ride quality or fatigue. I believe the performance is perfect for what I am doing with the car. No track or autoX. Purely road driving.

I am using stock t-bars and sway bars and I am using Koni Yellow Sport shocks all the way around.

Prekom also makes rear sway bar end links as well. I have a set on order now. The Lemforder ones I am currently using are bad about pulling the bushing out of the link. The Prekoms seem to be built in a way that prevents the bushing from pulling.

Hope this helps.