Updating my 88 Carrera suspension for autocross

[msterling]

I have been running my 88 911 Carrera in PCA and SCCA autocross for 3-4 years and I'm ready to improve a few things. Currently the suspension is stock except for a strut brace, turbo tie rods and a bump steer spacer on the steering rack. I have been in P3 (medium size region) for PCA and CS for SCCA. Tires are BFG Rival 225/45-15 on Fuchs 7&8's. Engine is stock.

The suspension is 26 years old but only 55k miles. The shocks are Boge. My budget is pretty limited so I will try to do some of the work and then let the shop do the alignment.

Tentative plans are for Poly Bronze or equivalent A-Arm and Spring Plate bushings, Koni Sport shocks front and back and upgraded torsion bars. I'm thinking 21-28 for the t-bars. This is already $2200+ in parts so I will plan to do stuff like adjustable sway bars and camber plates later.

I think I will still be in P3 for PCA but bumped to STR for SCCA.

Current suspension settings are: F. Camber. -.75 Caster + 5.8 F toe .08, R. Camber -1.75 R toe +.30

I am open to suggestions.

[safe]

Originally Posted by msterling

I have been running my 88 911 Carrera in PCA and SCCA autocross for 3-4 years and I'm ready to improve a few things. Currently the suspension is stock except for a strut brace, turbo tie rods and a bump steer spacer on the steering rack. I have been in P3 (medium size region) for PCA and CS for SCCA. Tires are BFG Rival 225/45-15 on Fuchs 7&8's. Engine is stock.

The suspension is 26 years old but only 55k miles. The shocks are Boge. My budget is pretty limited so I will try to do some of the work and then let the shop do the alignment.

Tentative plans are for Poly Bronze or equivalent A-Arm and Spring Plate bushings, Koni Sport shocks front and back and upgraded torsion bars. I'm thinking 21-28 for the t-bars. This is already $2200+ in parts so I will plan to do stuff like adjustable sway bars and camber plates later.

I think I will still be in P3 for PCA but bumped to STR for SCCA.

Current suspension settings are: F. Camber. -.75 Caster + 5.8 F toe .08, R. Camber -1.75 R toe +.30

I am open to suggestions.

Sounds like a good plan, but you need at least .5 degrees more camber all around in my opinion. I would probably have gone with 21/29 and Bilstein.

[winders]

Go 21mm/30mm on the torsion bars and get adjustable front and rear anti-roll bars. I prefer 22mm Tarett front and rear.

If you want to do well at an autocross, it is important to be able to adjust the chassis balance at the event.

You want a little bit of toe out at the front.

[Driven97]

For STR polybronze bushings and through-body front sways are not legal. Ditto for the bump steer spacers and turbo tie rods.

[msterling]

Originally Posted by safe

Sounds like a good plan, but you need at least .5 degrees more camber all around in my opinion. I would probably have gone with 21/29 and Bilstein.

I agree that I need more negative camber. The current setup is too much of a compromise and I will be going for more negative camber. The reason for the Konis is the external adjustment that the Bilsteins don't offer. 21/29 or 22/30 might be good and keep the front from pushing too much which is bad for autocross.

[msterling]

Originally Posted by winders

Go 21mm/30mm on the torsion bars and get adjustable front and rear anti-roll bars. I prefer 22mm Tarett front and rear.

If you want to do well at an autocross, it is important to be able to adjust the chassis balance at the event.

You want a little bit of toe out at the front.

I think choosing the tbar sizes is the toughest choice to make here. I'd love to get adjustable F/R sways but will probably wait until next year. I will be able to make some adjustments at the events with tire pressure and possibly shock adjustments. When I lowered the front for events there was probably a little toe out for better turn-in.

[msterling]

Originally Posted by Driven97

For STR polybronze bushings and through-body front sways are not legal. Ditto for the bump steer spacers and turbo tie rods.

I need to re-read the SCCA rules. I knew that a through-body front sway was not allowed but wasn't sure about the polybronze bushings as they are partly plastic.

Turbo tie rods? Really? Oops, I have had them for two years along with the two washers on the steering rack. Would that put me in Street Prepared?

[winders]

21/29 or 22/30 will give you too much push. Especially without the adjustable anti-roll bars.

You won't be able to make significant changes in chassis balance changing tire pressure or shock settings without negatively affecting grip. In my experience, autocross tires work best in a very tight pressure window.

[Driven97]

Depending on your scruples I really wouldn't sweat the polybronze on a local level. Step up to national SCCA events and you should have your ducks in a row though. Increased metal content in a bushing would move you to FP by letter of the law.

I'm at 21/33 bars and am still battling push, Fwiw. Big rear camber and the lsd really locked the rear end down.

[safe]

Originally Posted by msterling

I agree that I need more negative camber. The current setup is too much of a compromise and I will be going for more negative camber. The reason for the Konis is the external adjustment that the Bilsteins don't offer. 21/29 or 22/30 might be good and keep the front from pushing too much which is bad for autocross.

Is it the cab in your signature?

I have a targa with 21/27 and push isn't a problem for me, almost the opposite.

How does the balance feel today?

[msterling]

Originally Posted by safe

Is it the cab in your signature?

I have a targa with 21/27 and push isn't a problem for me, almost the opposite.

How does the balance feel today?

Yes, it is a cab. Actually, the balance is pretty good right now with the stock setup. I can get it to rotate when I need it. I have also had others drive the car and they agree. Things that are lacking are really crisp transitions and roll stiffness. I'd like to improve those things without ruining the balance. I would also expect improved grip.

[safe]

Originally Posted by msterling

Yes, it is a cab. Actually, the balance is pretty good right now with the stock setup. I can get it to rotate when I need it. I have also had others drive the car and they agree. Things that are lacking are really crisp transitions and roll stiffness. I'd like to improve those things without ruining the balance. I would also expect improved grip.

I'm speculating, but I think "optimum" t-bar size ratio is not the same for a cab/targa as a coupe.
I think the body shell is to weak to transfer the load properly between the front and rear. It would be interesting to get feedback from someone who has fitted a rollcage to a cab/targa and what that did to the balance.

There are people here on this forum with more experience than me, but if you like the balance you have, then 21/29 is probably good.

[Driven97]

If you want an STR legal option for bushings, Racer's Edge makes them in Delrin. Also waaaaay cheaper than the Elephant parts. I have them in the outer positions only, as it was easier just to swap those. I still have Neatrix rubber on the inners. Fair warning - they do squeak just a bit, but not nearly as bad as I was expecting. Nothing you can hear while driving, just if you bounce the suspension while the car is parked.

They also make ones for the front, if I knew about them I would have gone with those instead of the polyurethane ones from our host. Not interested in tearing the front end back apart quite yet, though.

I'd also put a nice priority on dialing in some more rear camber, especially with the soft rear torsions. Made a HUGE difference in the rear grip level in my experience.



This is with the 33mm out back, and the factory adjuster maxed out, which was about -1.5° or so on my car. Clearly not an ideal contact patch on the outer rear.

The 33s are 400% as stiff as the OE t-bars, so a softer torsion car is going to have a lot more roll. I went to -3.0° using the CamberMax after that event, and gained a lot of steady state rear grip and much more predictability near the limit. The tradeoff is a bit faster inner than outer tire wear, but not as bad as I expected.

They're a neat product, but if you look how they work, you can probably accomplish the same thing for free if you have a c-clamp, an appropriately sized piece of shim scrap, and a bit of patience laying around. Free is good.

I'm a big proponent of doing one step at a time when possible, so you can see the results & gains (if any) that each individual product provides. An "all at once" approach is fine, but it's such a shock to the wallet, and you end up having such high expectations for results. In reality, there's a ton of testing & tuning needed to exploit any mod. Having to dial in a bunch at once is much more difficult than the one at a time method.

Good luck, and keep us all posted on what works and what doesn't for you. There's not nearly enough of us autocrossing torsion bar cars.

[msterling]

Originally Posted by Driven97

If you want an STR legal option for bushings, Racer's Edge makes them in Delrin. Also waaaaay cheaper than the Elephant parts. I have them in the outer positions only, as it was easier just to swap those. I still have Neatrix rubber on the inners. Fair warning - they do squeak just a bit, but not nearly as bad as I was expecting. Nothing you can hear while driving, just if you bounce the suspension while the car is parked.

They also make ones for the front, if I knew about them I would have gone with those instead of the polyurethane ones from our host. Not interested in tearing the front end back apart quite yet, though.

I'd also put a nice priority on dialing in some more rear camber, especially with the soft rear torsions. Made a HUGE difference in the rear grip level in my experience.



This is with the 33mm out back, and the factory adjuster maxed out, which was about -1.5° or so on my car. Clearly not an ideal contact patch on the outer rear.

The 33s are 400% as stiff as the OE t-bars, so a softer torsion car is going to have a lot more roll. I went to -3.0° using the CamberMax after that event, and gained a lot of steady state rear grip and much more predictability near the limit. The tradeoff is a bit faster inner than outer tire wear, but not as bad as I expected.

They're a neat product, but if you look how they work, you can probably accomplish the same thing for free if you have a c-clamp, an appropriately sized piece of shim scrap, and a bit of patience laying around. Free is good.

I'm a big proponent of doing one step at a time when possible, so you can see the results & gains (if any) that each individual product provides. An "all at once" approach is fine, but it's such a shock to the wallet, and you end up having such high expectations for results. In reality, there's a ton of testing & tuning needed to exploit any mod. Having to dial in a bunch at once is much more difficult than the one at a time method.

Good luck, and keep us all posted on what works and what doesn't for you. There's not nearly enough of us autocrossing torsion bar cars.

Thanks for the tip on the Delrin bushings. My guy at the shop was talking about some hard plastic bushings but was not sure of the source.

I understand the reasoning for changing one thing at a time but this is now the off season and I won't get a chance try things out during the Ohio Winter. Shocks T-bars and bushings along with a revised alignment is a major change. Hopefully the combination will improve the performance.

Is there such a thing as an adjustable front sway bar that is not through the body? Would an adjustable rear bar do the job if I need to balance the car? I'm not sure.

Yep, I was the only Porsche at the last couple of SCCA events. With the upswing in 911 valuation I wonder if fewer will be used for competition. I don't see any reason to have the car if I can't have some real fun with it.

[Driven97]

If there's an adjustable underbody bar, I haven't been able to find it. I'm thinking about building my own out of speedway bits.

Rear bar should give you adjustability. Going too stiff will make it hard to put down power mid-corner, assuming you have an open diff.

[winders]

I am sure that Weltmeister still sells both the 19mm and 22mm front underbody adjustable sway bar kits.

[Driven97]

Link?

[RichardNew]

Do the adjustable sway bars first. When I ran a nationally competitive car I would adjust the bars between every run. Now that we're all allowed data loggers it's even more important.

Read the rules over an over. The other guys in your class have them memorized. As long as you run 3rd and 4the you're just fine. When you start to set fast time in your class people will be all over your car.

Richard Newton

[winders]

Originally Posted by Driven97

Link?

Google?

[Driven97]

Originally Posted by winders

Google?

Tried it?