911SC Torsion Upgrade?

[tyro]

For the last few years I have been autocrossing my 911. I am now thinking of upgrading the bars to something like 21/28 or so. Lately I have been driving on BFG Rival S tires, and also have a set of Toyo RR which I use. The shocks are Bilstein sport, which I've read may need revalving if the bars are upgraded?

Otherwise the car is certainly enjoyable as as, just not quite as competitive as I think it could be.

Here's a photo of this car's body roll, this location isn't a high speed venue:

[saxen]

i went 22 29- if I could do it all over again I would have gone 23 30. it will make a nice difference for you. I would consider doing sway bars at the same time.
good luck.

[Jnduda]

I did the 23 / 31 with adjustable sway bars; hardly any roll and great for the track. Would not want to try it on the street.

Worked with Elephant Racing who set up the package based on my needs.

[rdimarco]

I have 22/33 TBs, custom valved bilsteins, & adjustable bars. Works well and is fine on the street. Bushings & short stiff tires can contribute a lot to ride harshness.

[Driven97]

I'm at 23/33 and would like to go stiffer. 2600lb (without driver) Carrera 3.2. 7/8" (22.22mm) front sway, OE Carrera rear sway.

[juanbenae]

if you decide to go ahead and upsize the torsion bars paaahruz the classifieds looking for some of the larger 84+ sway bars. great upgrade with fresh bushings all around. I went with that and 21mm & 28mm tbars in my 78 sc when I was 1st startin to fiddle around with things. post a wtb add, a flipper will surely surface..

[safe]

For auto-x I would prefer a more rear biased set up like 21/29 (I have that now, went up from 21/27) for some street comfort. I like to get the front to bite and balance on the rear grip limit.

If tracking and auto-x is the main purpose I would go BIG, 33-34 rear and something to match that and my preferred driving style in the front.

[cajun]

Originally Posted by Driven97

I'm at 23/33 and would like to go stiffer. 2600lb (without driver) Carrera 3.2. 7/8" (22.22mm) front sway, OE Carrera rear sway.

I am about to have an identical setup to yours (in the process of going 33in the rear). Is there a particular reason you would like to go stiffer?

[Driven97]

I drove a few "real" STR cars recently, and my car is super slow to transition by comparison. The other cars react right now, mine has a significant lag time. It adds up.

I'm on the low end on the ride frequency spectrum (spring rate vs weight) compared to the fast guys, but not that far out of the ballpark. A hair stiffer would be nice - I'd love to try 24/34. That would put me from:

333/438lb wheel rates
to
394/493lb/in

The 36s are a huge jump up from the 34 - equivalent of a 619lb/in coil spring. That just seems like too much, even if you pull the rear sway, but I haven't crunched the swaybar numbers so I have no idea.

I'm going to try some better shock valving to see if that helps. My current valving basically blows and is now the 2nd biggest thing holding me back after the loose nut behind the wheel.

Honestly, my car is pretty good and pretty fast right now. Stiffer than I am now might be awesome on smooth sites, but may actually be slower on bumpy ones. There's no low hanging fruit to find seconds or even half seconds, I'm looking for tenths at this point at best.

Keep in mind I am limited to specific class rules - depending on what you're doing, you may not be.

[tyro]

Thanks for all the suggestions.

I run local events only for the most part in a "vintage" class which is pretty much anything that is >30 years old. A car that runs vintage could be any car, I usually battle (aka lose to) with a well-modified and well-driven Triumph Spitfire.

As far as bars go, does 22/30 or 21/30 or 21/29 seem like a good compromise? I'm really not picky, I just don't want to waste $ or time if I don't have to.

I get a lot of squat/dive with my current set, perhaps that's just the way stock bars are or maybe they are getting weak after 35 years and who knows how many miles.

[tyro]

BTW, here's a video of last week's event.

[Trackrash]

22 /30 is a good compromise for T bar size for a dual purpose car. For a dedicated track car, the bigger the better.

You need to replace/upgrade your bushings and have your shocks re-valved to match your T bars. Turbo tie-rods are also a good idea. One (at least) adjustable sway for fine tuning is a must. And an alignment that will optimize your setup...

[Driven97]

Also of note (and a full pardon if this is being presumptuous) don't forget all the other stuff. Having better flour is only one ingredient of a complicated cake recipe.

Do all the cheap / free stuff first - Play around with tire pressures, there's usually a fair amount of time to be found just with that. Remember there is an optimal pressure - more pressure and less pressure than optimal = less grip. You'll probably find the oddly balanced 911 likes pressure stagger, too - more in the rear most likely.

Max out the camber, make sure the toe is right, run big caster, make sure the corner balance is good. The camber & caster will improve your steady state grip. Rear toe can tweak your balance, especially on power, and front toe can tweak your front end response. A funky corner balance will make the car behave differently on LH & RH turns.

Then you need to identify what the car does well & what the car does poorly. That can direct your upgrade path. How does it accelerate? How does it brake? Does it slalom well or is it sluggish? How is your mid-corner balance? How is it at turn in? How is it when you go to WOT mid corner? Are you hitting the bumpstops?

And remember, everything is a trade-off. Making a car "better" at one thing can often make it worse somewhere else, whether on a track, between the cones, or on the street. My car, for example, is now "tolerable" on the street where it was originally quite comfortable, and is now likely loose to the point of scary at track speeds. My original goal was minor tweaks to make it locally AX competent, the scope has crept to attempting to hang with Nationals caliber STR cars. Setting a goal before you turn a wrench is a great idea to keep you focused.

[RichardNew]

This is going to get expensive real fast. When you change the spring rates you have to change the shocks. Then you tune the whole deal with adjustable sway bars.

Sooner or later you're going to start stealing the kids lunch money.

Richard Newton
Are You Buying a Porsche at the Monterey Auctions?

[tyro]

Exactly. I don't want to sink a ton into it, it's already a fun car as it sits.

I did stupid upgrades to a 951 and made it mostly useless for anything but a track.

"Regular" T-bars and maybe an upgraded ARB were what I was thinking for the 911. If anything, the originals are growing weak. I haven't driven other SCs, so I have no real bearing on whether mine are "the way it is".

[Flieger]

Properly made springs do not get weaker over time. It is possible for them to get abraded (if bushings have sagged) and rust, which can cause them to snap, but otherwise the spring rate will stay the same. So don't waste money with stock rates.

FWIW, I use 22/31 with no sway bars, front Konis, rear Bilstein yellows, I like it. Probably can do better on the dampers though. Car is 2200 pounds with fuel and driver.

[safe]

Well, I will go against the stream...

You will want to change bushings at the same time as t-bars, because you don't want to do that job twice if you can avoid it...
But you can do the shocks and sways at a later date, it may not be as good as it can be, but its not gonna be bad.

[tyro]

Front bushings are done, only the rear remains.

At this point, it might be an upgrade for next year since I'm only a few months from winter storage again (UGH).

[Trackrash]

Originally Posted by tyro

Front bushings are done, only the rear remains.

At this point, it might be an upgrade for next year since I'm only a few months from winter storage again (UGH).

Plan now. Upgrade this winter. Drive this spring.

[DG624]

I have 21mm front with adjustable front sway bar and 30 rear with stock sway bar. This gives, according to Driven 97, a wheel rate of 247 F and 300 R which can be evened out with the sway bars. I also changed the bushings F/R and went to mono ball for rear control arm. This along with corner weight to reduce rear bias and eliminating 250 lbs and reducing static ride height by 1inch and going to 15 inch wheels helps considerably but my current gear package hurts my second gear power.

I want to have a car that is adjustable and can compensate for different surfaces. Reducing ride height and increasing negative camber helps to reduce understeer but so can driving style. I am trying to get the car to a good power to weight ratio and improve response. I have not experimented with the new setup since the car has been in the shop.