Been Searching around for comprehensive info on merits/function/dynamics of installing the 2pc gt3 arms on our turbo. Most of the info collected was from vendor or forum posts in relation to the gt3/gt2. The uprights on our turbo is different so not sure if the figures apply 1 to 1 but the theory should be inline. Please fine the findings as follows. Experts please chime in.

There are 3 different lower arms available from the factory. These are interchangeable between the 996 turbo/gt2/gt3.


Standard 1pc that comes with the 996 turbo: 996-341-053-16-M80/996-341-053-16-M253 Note the thrust bushing has only a center hole.


2pc with rubber bushings standard for the GT3 street car:996-341-122-90-M100/996-341-121-90-M100/996-341-441-90-M100. Can be used for either front or rear. Note the thrust bushing has an offset hole.


Then there's the 2pc GT3 cup version. The photos here show a different to the standard gt3 street lower arms in that the thrust bushings are solid with wider adjustability/monoball end link and longertotal arm length (unconfirmed exactly how much) . The fact that the standard gt3 lower arms work for both front/rear and there are 4 different parts/part#s for the "cup" arms front and rear is annecdotal proof of difference in length. 996.341.053.91/996.341.054.91/996.331.053.90/996.331.054.90 Upon closer inspection, from the TRG website, from description of the product, it appears only the rear lower arms have the solid thrust/monoball ends. so it could just be differences in bushings?


Shims go between the 2 sections and come in 1mm/2mm/2mm/7mm sizes. Each additional 10mm provides 1degree of neg. camber. 10mm is max. before ends run out of threads.


The stock upper mounts can be clocked 180 to provide an camber over and above stock range. I believe stock can go max neg 1degree. clocking this can provide neg 2.5 degrees (depending on ride height). Shimming the lower arm can yield higher than neg 3degrees of camber, but affect caster. The caster range for the gt3 is between 7.5-8.5degrees.

The standard gt3 street lower arm allows for some caster correction via "offcenter" thrust bushing hole to bring caster back with in range.

To be confirmed: Suspect the gt3 cup comes with the hard caster puck, and allows for more correction, because the bushing is solid and thuse the offcenter hole is located farther to the edge of the bushing. My guess is most solid thrust bushings from aftermarket vendors are similar.

Apparently, if camber is changed from the strut tower, caster/track width is not affected. If camber is increased via lower arm/shims, caster/track width is affected, bringing the wheel effectively forward. this causes off spec caster and unwanted rubbing issues. This is because the diagonal arm is fixed, and widening the track, has a pivoting affect.

Not sure caster adjustability differences between the cup and standard gt3 lower thrust bushing. My guess is if the cup arm is infact longer, the net affect of offset hole to caster functions to bring caster back within 7.5-8.5 range. Adjustability is fixed, ie it's either of the 2 holes.

Diagonal adjustable arms offer fine tuning for caster. Can't find information on exactly how much. And not sure if one can effectively use one or the other (ie adjustable puck with non-adjust diag. arm or non-adjustable puck with adjustable diag. arm). Additional difference with adjustable arm is monoball end.


Great detailed explaination on dynamics of all this in this link.
http://forums.rennlist.com/rennforum...djustable.html

Again, most of the info provided was given in relation to GT3/GT2 cars. The uprights on our standard turbo is different, and not sure if this variable has an affect on overall dynamics.

My goal is higher caster with in normal range, about neg 2.5-3degrees of camber, and no rubbing issues using slightly wider tires and more aggressive offset wheels. Plan is to try the gt3 Cup front lower arms (if they infact come with solid thrust bushings). If the arm is infact longer, all variables constant, this should already offer increased camber. Will use shims and Mode adjustable strut tops (10mm camber range of adjustment) to dial in correct camber, and play with caster bush offset holes to achieve max caster within range that doesn't creat rubbing issues. On the rear, will use the gt3 standard lower arms and mode top mounts.



Have attached couple photos, one to illustrate dynamics. and gt3 standard 2pc arms versus rear standard lower arm. * NOTE all info gathered here is from the internet, I have not tried myself and can not confirm validity. If experts have experience, please chime in.

 

edited above post to add info, *bump* to bring back up in que.

Thing I'm still not that certain of is rim to spring clearance. Have read people switching to a smaller diameter spring to clear for much wider wheel/tires. I'll be going with 245 max and hopefully wont need to do this. Anyone have experience here? TIA
https://www.6speedonline.com/forums/...made-work.html
http://www.renntrack.com/forums/show...s-to-996-Turbo

Don't think the 996's have the litronics issue the 997's do but not sure.

 

You may also want to post this in the GT3 section here and the other board since those guys may deal with this more often.

 

didn't think of that... thanks.

https://www.6speedonline.com/forums/...ml#post2888656

 

subscribed

 

I have heard of people using 265's or 275's in front with lots of camber. Pretty much dials out all understeer.

 

yes have seen a couple posts on this but these cars also had other extensive mods such as > than -2.5 front camber, 2.5"diameter springs, gt2/gt3 uprights, RWD conversion, fender liner mods, radiator mods, fender rolling, slight rubbing full clock etc... none of which I intend to do and/or want to avoid. This and different wheel sizes, tire brand/sizes, ride height are cause for difficulties in determining exactly what's needed for different applications. If anyone's interested in going this route, there's a helpful link in first post and this one: https://www.6speedonline.com/forums/996-turbo-gt2/184900-10-inches-too-big.html


more piece meal info collected.

update on lower arm info transcribed from gt3 forum member post above. the cup and gt3 street 2pc lower arms are the same length as the turbo orig 1pc. Both cup and gt3 street arms come with the same rubber bushings. Only difference is in arm material, stronger and possibly lighter. Front/Rear arms interchangeable.

There's a 3rd arm pictured in 1st post erroneously as "cup" arms. These are sometimes referred to as "RSR" which comes packed with monoball inner arm ends and solid adj thrust bush. Cost of the RSR arm is similar to sourcing monoball bushings/inner arms + gt3 outter arm + aftermarket adj solid thrust bush. conflicting info whether the non-shimmed RSR arm is longer (but would make sense since this car's got a much wider stance).

Shim info: the lower arms can take max 14mm of shims, 10mm yields roughly additional -1 camber. Max camber possible depends on ride height but on avg. a stock car can get 1.2~1.5 neg camber. Not sure if this is with or w/out reversing the strut mounts.

PSM sensor (minor mod on lower arm to fit sensor bracket)

having partial set of mono/pillow ball rod ends is not ideal. While there's value in added adjustability, weight reduction, the remaining rubber bushings will sustain even higher stress and flex more. monoballs should be pretensioned and difficult to move, if moves easily, increases chances of wear and noise.

Note on Toe: it's my understanding suspension compression increases toe and vice versa. thus an important consideration such in case of hard braking entry or hard accel out, type of corners, road surface, straight speed.

Have got most of the arms arleady. Looking to replace as many of the rubber bushings with monoball as possible. Only arms not upgrading at this time are the thrust rod arms. Similar to lower arms, front and rear parts are the same. In addition to monoball rod end, these arms is allow fine caster adjustment. The gt3 street rubber thrust bush and after market/RSR solid bush offer 2 settings, center and off center only. The third smaller hole on solid type is for a bolt to clamp the 2 pieces together. Have read verbage "clocking" used in relation to caster adjustment. Not sure if that means the puck can be physically rotated, then clamped into position, to provide for additional caster fine adjustment.

Not sure if adjusting rear upper arms for camber will affect caster significantly.

Hoping to successfully achieve camber -2 or less, caster on high range 8, and slightly wider tires, 9J/11.5J wheels, less than stock but not slammed ride height. Will try to find a balance between strut top side and lower arm side camber adjustment as a) too much upside may cause rubbing issues between rim and spring and b) too much underside may cause difficulties in dialing in caster target. No idea on toe yet. (Current suspension mods KW V3, H&R sways, AP sway links.)

List so far:
Front
gt3 2pc adjustable lower arms - allow camber shims with out altering caster, increased track
Front adj. bumpsteer/toe control arm - toe adjustments, correct steering geometry for lowered cars
monoball bush for inner gt3 lower arm
adj. solid thrust bush in gt3 outter arm - caster adjustability/ add feel
-1 degree camber built in monoball strut mount - camber and delete mush feel
spherical rod end dust boots packed with white lithium grease - help maintain cleanliness, minimize wear and delay noise/play.

Rear
adjustable dog bones upper arms - camber adjustment
rear adj toe control arm- toe adjustment and monoball
lower arm monoball bush
solid adj thrust bush - prob won't need to adjust caster but doesn't cost a lot more, nice option to have.
mode monoball strut mount 0 fixed camber - delete mush feel
spherical rod end dust boots packed with white lithium grease - help maintain cleanliness, minimize wear and delay noise/play.

Relevant Links:
https://www.6speedonline.com/forums/...ggestions.html
https://www.6speedonline.com/forums/...ts-needed.html
https://www.6speedonline.com/forums/...ol-arms-3.html
https://www.6speedonline.com/forums/...os-inside.html
http://www.renntrack.com/forums/showthread.php?1065-Alignment-help

Summary of parts article by sharkwerks:
http://sharkwerks.com/porsche/technical-articles/74-project-suspension-tuning-2009-sharkwerks-997s-ztadpol.html

 

GREAT THREAD! I just resuscitated it!

 

Magnus,

Lots of data in your post. I won't address all of that, just tell you what I did in my car and how it worked out.

My car came with PSS9 suspension. I could not get as much negative camber as desired with just this. I do not have enough clearance in the strut well to get more than -1.5 degrees up front, even with the camber slots extended. The split GT3 arms allow me to get easily -2.5 degrees and more is available. I get that by installing 14mm shims. Toe has to be adjusted to compensate. I'd recommend one of the adjustable bushings to help you re-adjust caster. I didn't do this, but it's really tight between my front tires and the front fender wells.

In the rear, I have adjustable upper dogbones and an adjustable toe link. I can easily get as much negative camber as desired. I have stock control arms back there.

Hope that helps.

Jon

 

What upper adjustable dogbones are you running?

 

Great info! Subscribed !

 

Awesome way to dial in your camber, and as a result your alignment...