Bagnall928

Hi
im interested in the opinions of 928 racers as to what shock/spring/swaybar combinations have worked for them .
for slow tight tracks and fast flowing tracks
car will weigh about 2800#s
approx. 300hp at the wheels
DOT race tires
thanks,B

Kaplan69

I'm currently building basically the same setup. Granted, I have zero "race 928" experience, but decades of vintage racing builds, and very successful. Some would argue that the 928 is a completely different animal, but I would disagree. Since you're building a dedicated race car, my strong suggestion would be to eliminate ALL rubber bushings in the suspension, except one- the Weissach bushing. Some others will suggest even neutralizing it's function by "pinning it", which is easy enough to do at any time later, should you decide it's function is detrimental. Delete all the rubber, which is at least 30 years old. Early cars accept all of the later S4 front suspension as a direct bolt-on, and many (me too) believe this is a worthwhile upgrade. S4 parts, brakes, geometry are all improved. Rear suspensions are basically all the same, save brakes... I'm using PowerFlex Black front 3 piece poly bushes, and everything in the rear is being converted to solid aluminum bushings, or spherical ball joints. My philosophy is based around Suspension Guru, ex-GM suspension engineer Herb Adams books ( "sticktion" is bad...) He (and I) lean toward trying to make the chassis (unibody) stiff in torsion (resist twisting) and free up the suspension to move in its designed articulations. There are some coilover options out there (GAZ, KW, MCS), sway bar options are few and far between. I'm going to fabricate my own adjustable rear bar due to the almost hidden nature of where the factory rear bar is. Good luck!! Ken

Bagnall928

Thanks Ken,
im curious as to how the S4 suspension pieces improve the front geometry? Are the A arms different in dimension ?
I have the better brakes and the power flex poly bushings.
it seems that the Devek sway bar isn’t available so the28mm bar with hiem links may be the option.reinforce bar mounts?
Im curious about the GAZ coil overs. The dbl.adjustable shock, is it a quality shock for its price range?
Track spring rate range?
Brian

Kaplan69

There are people probably on this forum who are currently, or have run the GAZ coilovers, so I can;t say how "good" they are... S4 stuff has quite a few improvements, but if you've already changed to better brakes on the earlier suspension, I wouldn't bother and save the money to put towards other stuff. IcemanG17 has quite a bit of experience with a similar setup to yours. I'd PM him too. Spring rates will have to be increased significantly if you eliminate all of the factory Porsche pivot rubber which is designed as part of the spring rate to the original car. Keep in mind that "wheel to spring" ratio is 2 to 1 on the front (800lb spring is 400lb at the wheel) and 1.1 to 1 at the rear (440lb spring is 400lb at the wheel) . These are only math examples. I'm pretty sure there is a 2mm diameter increase in later (S4) sway bars over early cars. Should be a cheap, bolt on improvement.

puyi

Yes, front suspension are really different from OB-S2 to S4 and later

The geometric pattern is relatively different and it has a real effect on the ground. S4 is better for track use

There is essentially 2 philosophy for the 928 post S4, first is big sway bar and relatively low spring rate, coil must be adjusted relatively to the spring stiffness. second is stock or essentially stock sway bar and spring of high stiffness.
Porsche engineers that had worked on it had chosen second one at time, so am I.
I already had driven both and i prefer second one because, it seems to me that it was best handling @ the limit, but it is very much dependant of road quality and you should consider the possibilyty of changing spring setup dependant of the tracks.

Unless there is much newer coil overs, my setup is based on a combo eibach spring and bisltein coilover.

But the search engine on that forum is your best friend, plenty of discussion about choices of many and others

Bagnall928

Thanks Puyi,
i’m curious as to the S4 front geometry. The mounting locations I think are the same as the 79 that I have. As to track use, if the S4 provides better static camber/castor settings that would be a plus. If the upper and lower AArms are different dimensions or the spindle dimensions, they would affect the roll center location which may be a plus.
Do you know the difference?
Did Porsche engineers work out a race setup for the 928?
What Bilstein shock worked for you on the track and what spring rate? Smooth track

icsamerica

Safty issue here. The early suspension was designed with tension that pulls the ball joint out of it's alu socket. Very precaious situation when pushing a 928 past it's design limits and those limits are easily reached with any modern UHP tire. The later S4 suspension wqas redesigned in such a way that it pushes the ball joint into the socket this creating a safer situation. This necessated some design changes to the spindles to accomidate the change. These design changes also allow for larger brakes too. The upper control arm is shorter on the S4 and this allow for slighly more camber gain when under compression. If you're planning on track use then S4 suspension is a must IMHO

All the power flex stuff is amazing. The free moving LCA bushings transform sthe car from what feels like like driving in mud to what feels more like a 90's BMW. That is to say much more responsive and more feed back.

Stock Upper rear control arm are useless with high performance tires. New arms with poly or heim joints are a big plus. I fabricated my own with a Heim at the spindle side and poly on the inside. Made the rear much more controlable and no precepible additional harness.

You cant go low with a 928 OR you have to use very stiff front springs. For anything less than 600Lbs/in, the upper spring purches have to be modifed for additional shock travel with a spacer at the top of the shock mount or the shock will bottom out. In the video below I hit the curbing, upset the chassis and spun.

You may need a power steering cooler. After track sessiones my PS fluid would be smoking, but I run a higher PSI pump and did many rack mods for precision and more assist.

I'm very happy with how my 928 performs on the track but I need more power and the list of things I've done and need to do is still long. 928 is not a natural track car, it wasnt built for that so many things need modification and fabrication.

GUMBALL

Possible the best person to ask is Mark at 928 International. He campaigned a 928 successfully in the IMSA series.

.

Mark Anderson

Thanks but because my car was modified in so many ways lots would not apply. Kibort is probably a better source as his car was much closer to stock.
engine lowered
suspension points altered
2550 lbs
12" slicks on all 4 corners
lighter engine ( carbon intake, tilton clutch, no steering pump)
and the list goes on

IcemanG17

My old car as seen in avatar has these mods: Full heim jointed custom bilsteins all around. Large front sway bar (can't remember brand), no rear bar, 1025lb front springs, 450lb rear...weighs 2620lbs with 1/4 tank (no driver) back then was 265whp....I ran 18x10x65mm all around with 275 slicks. GTS front brakes, S4 rear with Raybestos racing pads. No aero....just good old stock 1979. The old girl put down impressive lap times given no aero and modest power when I was racing her 10 years ago. My best at thunderhill over the top of 2:02 equaled what Kibort put down before he had his stroker....his car then was around 320whp-2800lbs but had aero, with R comps.

I would say the expert in 928 suspension is Greg Brown. He did a lot of work on that 700hp GTS recently

Bagnall928

I very much appreciate everyone’s response! I’ve built race cars before and it’s best to find out what works before rather than later…
my main questions for the moment,
race proven ( blue collar) shocks adj. or not.
budget 18” rims that fit stock fenders
Does the power steering need a cooler
keep the diagonal braking
stock limited slip need higher bias
why would S4 front suspension be better than early with bigger brakes
thanks Brian

The Forgotten On

The S4 suspension was designed for the larger calipers and you wont run the risk of having the rotors rub into the lower ball joint.

The lower ball joints were also moved to mount on top of the hub's lower attach point so that the ball is forced into its mount instead of pulled out of it like in the earlier design.

This avoids a common failure causing the entire suspension to collapse under load, fortunately this is usually at parking lot speeds.

I would also get a set of shocks and have the valving matched to your springs. Bilstein offers this service as part of a rebuilt starting at $75 a shock last I knew.

Adjustable suspension has its place but it can greatly complicate things unless you plan on many tuning sessions to dial it in.

18 inch wheels that fit that are cheap are the wheels off of a first gen Panamera. They're BBS so they are quality and can be had for as little as $300 for a set if you get lucky.

Power steering doesn't need a cooler fortunately but you could add the factory cooler line used on the S4+ if you really wanted to.

On the track the LSD wont help much and might actually increase understeer. Best bet is to fit a larger rear sway bar to negate understeer and possibly induce some oversteer.

Darklands

If you’re starting from scratch you should consider the new KW V3 complete suspension set.
It‘s 3.300 € and it‘s adjustable.
Maybe if you call them they can change things for the Track use.

https://www.kwsuspensions.de/shop?c_...r=2993&pgs=160

mark kibort

after all these years, im still in the dark as to what works best. i do have to say, the devek level 2 set up, which was 750 front and 450 rear springs with koni dual adustables were the best. after i revalved them at the koni shop at Sears point, since they were maxed out both on rebound and compression, the car never really handled the same when i put the previous max setting to the mid way point on the new shock internals. anyway, the cut stock springs and the sport konis worked well on Scots racer. my car is 2750lbs, 12 slicks on all 4 corners with all stock bushings and attachments. (sans the plastic bushings on the steering rack) lowered to about 110mm front and 140mm rear.
devek swaybar up front, drop link stiffeners in the rear (uses stock sway bar but makes it stiffer). yes, keep all the brake plumbing, stock thats fine until you out grow it. LSD is certainly good, but not too much and not open diff., or you will need to manage single wheel spin out of off camber turns and hairpins. too much LSD and you will get oversteer too. stock LSDs work well.
wheels are tough to find custom offsets, but if you find some rear 11s and front 9.5s with 8" backspacing, you are good to run 275s all the way around, and more than likely 305 rear with a little wood bat rolling to crush the fender lip inward and flat.... i have other tricks to run even 12" slicks up front, with stock fenders but moved out a bit , and a 7.5" backspacing on 10" rims.

Crumpler

Following with interest.
Glad to see that people still want to track our
”obscure” racing platform, as someone told me at the track recently

Weekend DE guy only, but the 86.5 is a devoted track car now. Stripped down, Bilsteins and the Eilback springs that I believe 928intl had made or obtained back in the day.

I supercharged, now twin SC, to keep up with the flipping competition. Increased tire size on back to hold it 245 front, 305 rear, created or made the existing understeer worse.

I found an old DEVEK sway bar (not sure what stage) but it is bigger. And re-enforced the mounts. That helped somewhat.

What’s interesting to me, was I remember Carl selling a front end stability bar.
So, like many of the 928 Motorsports items, resold with his badge on it, I found a Moly-bar set up and ran it across between the forward LCA bolts.
While expecting nothing, I got a pretty dramatic understeer. It was one of those “smiling but puckered” moments.

I need to get the bugs out this season but maybe you guys can expand on why this would make such a difference? I remember GB saying something about our front stock bushings loading progressively, and this would prevent that?
Best
Dave