smceo

Hi guys,

After catching up on literature and hours of countless reading and research, scrutinizing part numbers, and attempting to identify the difference between 996 GT3 / 997 GT3+RS / 997 Cup / RSR Arms, I'm still a bit muddled on some of the chief differences/characteristics between them all. I am aware that there are many variants on these arms (Thank you @powdrhound for all the published literature and experience you have shared).

Here is what I understand so far:

1. All 996 and 997 arms are interchangeable.
2. There are many different types of arms. 997 GT3/RS Arms =/= 997 GT3 Cup Arms / 997 RSR Arms. This is the most confusing part.
3. RSR Arms are the same all around and can be used on all 4 corners, with one part number. AKA I would just need to source the RSR Arms x 4, and there is no different PN# for Front + Rear.
4. Cup/RSR cars all have monoballs in them (inner bearing joint + thrust bearing + outer bearing). Street cars use rubber bushings on all 3.
5. The "Short" inner bearings (rubber) are used on the 996/997 street car. Effectively, a shorter inner bearing would equate to a narrower track width compared to a "long" inner bearing which provides a wider track width.
6. The "Long" inner bearings are used on the Cup + RSR cars. The RSR/Cup Cars use the inner monoballs, and the inners are the "long" version and effectively this provides an increase in track width/camber as the length of the inner joints is what determines this geometry. I believe the rear of the Cup/RSR cars use the "short" version of the monoballs.
7. LCAs that are "smooth" are forged. The "rough" finish is cast.
8. 996 up to 997.1 GT3/RS use the "rough" textured arms. 997.2RS and Cup/RSR cars use the "smooth" forged arms.
9. The 997 RSR LCAs are 5mm shorter than the body of the Motorsport 996 Cup Arms. The body of the 996 Cup arms are effectively the same as the street 996 or 997.1 GT3 LCAs (textured). Essentially this means that the RSR LCAs are shorter than the 997.1 GT3/GT3RS LCAs (?). However, the RSR/Cup cars use longer "inners" to make up for it and increase the track width. That, and shims as well.
10. RSR/Cup cars use a longer inner monoball end for the fronts, and a shorter inner monoball end for the rears.
11. Finish of GT3/RS LCA looks different, metal looks more unfinished and the ridges on the arm are different
12. 2008 cup cars still used the 2006 arms:
    997.341.142.90
    997.341.141.90
    
    they changed them in 2010 to
    
    997.341.042.95
    997.341.041.95
    

With that being said, here are my intended goals for my 997.1 RS

• 50/50 Street + Track Use.
• Target alignment between -3.5 ~ -5 deg all around. As far as I understand, I will want the RSR arms all around on all 4 corners, with a longer RSR monoball in the front + shorter RSR monoball in the rear. (see line #3, #6 + #10 above for my intuition and understanding of this topic thus far).
• Car will be equipped with triple-adjustable JRZ RSPRO 3's. We are going to have these assembled and built with rates primarily geared for track use, so stiffer than normal, however; the adjustable high/low speed compression should provide the ability to fine tune the dampers for a compliant street setup if need to be.
• If paired with the RSR Arms on all 4 corners, on the outers, I would like to retain the sealed rubber bushings for durability against the elements (Will the RSR arms even fit OE rubber bushings? Inners I will change to the "long"/"short" version inner monoballs for the front/rear respectively. The thrust bearing I will be changing to solid adjustable as well for added caster adjustment due to an increase in track width.
• I understand completely there are a handful of aftermarket solutions (RSS/Elephant/BBI/Tarret) - This is not my question but I will also consider this route. Aside from the LCAs, I plan to change every arm (dogbones/toe/thrust/rear uppers) for adjustability sake. This discussion is solely to address the topic of LCAs as my understanding of it is still quite foggy to be quite honest.

I have attached photos at the bottom of this post referencing what I understand to be the 997 RSR arms that I need (Thank you @powdrhound for the photos).

Now, here is the confusing part + what I need help with
- 997 GT3 Cup arms use the PN# 997.341.341.90 (picture 3-4). I believe pictured in #3-4 is the GT3 Cup arms but just with rubber bushings. However, based on the experience of others, according to PMNA/Motorsport, these are discontinued so this leaves me no choice but to run the RSR arms.
- The first two photos are photos of the RSR arms (picture 1-2, circled in red). I believe in the 2nd photo, the arm that is not circled (shorter) is the OEM 997 GT3/GT3RS arm (?)
- There is conflicting info stating that RSR arms are longer than the regular 997 GT3/GT3RS arms. However, my intuition in line #9 has me understanding that RSR LCAs are shorter than the 997 GT3/RS arms. I need some clarification on this because ideally I do need a wider track width and I would like for the RSR arms to actually be longer.
- If the RSR arms are actually longer, and if I am correct to assume that in picture #2, the arm that is not circled (shorter) is the OEM 997 GT3/GT3RS, then I know that the RSR arms are what I need.
- If I understand this correctly, for my intended goals, I should run the following:

• 997 GT3 RSR Arms all around
• RSR Longer Inner Monoballs (front) + RSR Shorter Inner Monoballs (rear)
• Dial Camber with shims.
• Solid adjustable Thrust Arm Bearings (Tarret/BBI/Many aftermarket companies make this)
• Rubber OEM outer bushings (will these even fit RSR Arms?)

If anyone has any RSR Arms lying around with the monoball inners, I would be happy to take them off your hands as I'm not sure if PMNA is out. Worst case scenario, if rubber OE outer bushings are not compatible with RSR arms, I can just run the rebuildable heavy duty outer monoballs (Part number #13 and #14 in photo #5 which is a diagram of the RSR and corresponding PN#s.

However, if the RSR Arms are indeed shorter than my OEM 997.1 GT3RS arms, wouldn't I also just have luck keeping my OEM LCAs (F + R) and upgrading the inner bearings to the RSR longer monoballs (F + R) and shimming it for camber + putting solid thrust arm bearings in to achieve my target alignment? Outer bushings stay rubber for streetability. Again, the goal is -3.5 to -5 deg all around to fit a larger tire and more aggressive offset, as well as more even tire wear at the limit. While the JRZ RSPRO3's will come equipped with adjustable tophats, I do not want to do the bulk of camber adjustment via tophat as there is potential for fouling at the strut tunnel housing, and many have reported that the majority of adjustment and camber should be coming from the LCAs/Shims.

Any info is appreciated. Thank you in advance!

RAudi Driver

That'a s lot of work for a car you have yet to really start driving. I say drive the car in its stock form for a while and then start modding slowly using PMA parts when you can source them.

Also, I think the last thing you want for a 50/50 car is that much negative camber. That's just too much.

The shocks you are proposing seem super overkill and will be hard to set up properly so maybe just a set of the Ohlin TTX POF MROO's for the car will be a better choice.

Whatever you decide on, keep up updated in your Journal.

powdrhound

Availability of the RSR arms has been spotty with PM. I have 6 new ones on hand but inclined to keep them as spares. Prices have gone thought the roof on these recently. Plan for $$$ for all 4 corners.

With that said, a couple of things: The rubber boots are not compatible with these. The outer monoball is not rebuildable. The parts reference (#13 and 14) are the Vascomax trunnion pin and the bolt, not the monoball. The trunnion pin is available in 3 different length to allow you to adjust roll centers. If you plan to drive the car in the wet with regularity, I would probably not install these due to the exposed heim joints.

I run these on my car on all 4 corners with the short monoballs. The fronts have 12mm of shims which gives me -4.5 camber with the tops flipped to high camber. Rears I don't use any shims for -3.6 camber. I run 275/645 and 315/680 DH tires. The RS3 Pros you are considering are great shocks. Not hugely difficult to set up if you have some experience with suspension tuning. Have done many set ups on these cars with these shocks. For semi aggressive street / track use I would run 1000lb front mains and 1300lb rear main on a 7.1RS. Tenders you want a 40/60 F/R block load. Many will think these rates are high but the shocks are excellent and can handle these without being too harsh, not much different from stock. I run the JRZ 3 way Motorsport version of these and use 1700 lb fronts and 2100lb rears. Superb shocks and works fantastic even on bumpy tracks.

With all that said, my recommendation is stay away from any of the aftermarket parts. Most is relative low end bling in comparison to the PM pars. I have all the PM RSR bits and with about 5 years on use on it and it's been flawless. This includes LCAs, upper arms, thrust arms, toe arms, and tie rods. I do not street drive the car. If I did, I'd probably stay stock...

Good luck...

smceo

This is typically the setup I have run on my previous builds ~-4-4.5 deg on the street with monoballs and great tire wear! I would just like to prepare for the parts as I understand supply is pretty backed up on the manufacturing side (and also just for sake of understanding) - Research is always the exciting part!

smceo

Beautiful info - Do you know if the RSR LCAs are indeed shorter or longer than the OE 997.1 RS LCAs? Based my understanding, it does seem that the bulk of camber adjustment you are getting are from the 12mm of shims w/ the top hats flipped to max camber, correct? Is there a separate PN# I should be looking for in order to order the RSR short/long inner monoballs?

powdrhound

I measured the body of the RSR (smooth) LCA to be 5mm shorter than the cast (rough) LCA. I run the upper mounts flipped and then pushed fully inboard. As such, I need less shims and can get away with the shorter inners. I set camber via the shims. I do this in order to push the wheel assembly as far inboard as possible so I can run a 10" front wheel with a 275 tire. If I recall, the longer inner is 15mm longer than the short one so I could probably use that one too without shims. If you were to run the upper mounts in the standard configuration you could use the longer monoball joints to compensate. Hope that makes sense. The part numbers is different for the longer inners. It's in PET. I don't have it in front of me.

mistermct

Bumping an old thread as I seem to have found 997 Cup arms 997.341.341.90 that are the same length as RSR arms aka shorter than street. I'm about to replace my stock 996 gt3 arms and the caster hole on the new arms is 5mm closer to the inner shim face. Anyone seen this before?

mistermct

Closing the loop here. I talked to a local shop.. this didn't seem like news to him. So I guess it's normal. I'm getting the same measurements by adding 5mm of shims. so far, so good