NJ-GT

The inner attachment points are common across all the 996 with the exception of the RS that uses a different rear subframe. The outer attachment points are model dependent.

The outer front attachment for the control arm and the steering link on the 996 GT3 RS sits lower, to reduce bump steer. Bump steer is not that critical at the front, but it bothers.

At the rear, the 996 GT3 really needs a bump steer fix, and a solution to avoid unwanted toe changes. The rear toe eccentrics wear-out, the toe arms will move in and out causing a dangerous handling, and damage to the subframe.

Depending on the desired ride height, tuning is necessary using GT3 Cup toe links and spacers, or the expensive 996 GT3 RS rear subframe and uprights, and additional tuning with spacers.

There are three different rear uprights for the 996 series with the same attachment points: an early 996, a later 996 (including 996 C2, C4, Turbo, C4S, GT2, GT3), and the unique 996 GT3 RS uprights with lower outside attachment point for the control arm and toe link.

karlooz

hmm, i was told that the front bearings wer the same. i guess they (i) are mistaken.

so the RS mounts are higher than the gt3 which are higher than the 996. this is to compensate for a much lower ride height yes?

thx for the info. now i know what to upgrade

Cupcar

According to my factory RS book, the only differerence between the RS side member and the normal GT3 side member is at the adjuster eccentric which is designed for more stroke and more negative camber adjustment. No mention is made of changing the height of the installation in the car.

Personally, I would think twice about adding the RS side members, they are expensive and a lot of work to replace just for more negative camber adjustment.

Cupcar

BTW The front wheel bearing is 999.053.041.02 on the 996 and 999.053.042.10 on the GT3

karlooz

ahhh, ok. so the gt3/rs have the same higher mounting point (relative to the 996) to improve roll center on lowered cars. i can upgrade to the regular gt3 subframe/sidemembers, lock out the eccentrics, run 2 piece track arms and dial in camber with shims and erp upper links. those ebay subframes should do the trick then

ok enough of my rambling.

NJ-GT

Correct, but the longer stroke goes on a 30 degrees angle. So, the less negative camber obtained by moving the control arm in, the better reduction in bump steer. After that re-adjust for more negative camber with shims on the two pieces RS control arm (and this increases track), then re-adjust toe, because adding rear camber shims increases toe out (opposite to the front that increases toe-in)

IMHO, the rear RS uprights and RS subframes are not worth it, other than the 8 lbs weight reduction. The rear geometry is fixed better with the Cup toe links (plus spacer rings), two pieces RS control arms, and a street height (anything over 105mm on stock tires).

At the front, the rear GT3 Cup links can be installed instead of the stock steering links. Adding spacers will remove the bump steer.

viperbob

Another difference with the C2 uupright over the GT3 is that the C2 has a narrower bolt spacing for the brake caliper. You can not simply bolt on a 996TT or GT3 caliper.

thusly

Here are just some of the suspension part numbers for a GT-3 RS. I bought two RS suspension kits from Gert @ Carnewal; I think there were over 60 separate parts. Price was no where near $11k.

996-343-041-97 (2) shock absorber
996-343-531-97-504 (1) coil spring set
996-343-070-93 (2) swaybar droplink
996-331-111-90 (1) rear wheel carrier (L)
996-331-112-90 (1) rear wheel carrier (R)
996-341-121-90 (1) control arm (L)
996-341-122-90 (1) control arm (R)
996-341-441-90 (2) bearing flange control arm
996-331-551-90 (1) support
996-331-051-92 (1) rear axle side section bracket (L)
996-331-052-92 (1) rear axle side section bracket (R)

See http://www.6speedonline.com/forums/s...655#post626655 for complete parts listing.

Kevin

I just won the auction for the rear subframe, what a deal.

It should work nicely with my JRZ's and 6 bolt front RS wheel carriers.

Cupcar

Below is a picture from the RS book I quoted. I drew in the red arrow. Do you mean the eccentric slot is at an angle as shown by my red arrow (or an arrow going the other direction), rather than just being parallel to the ground?

Also, if I understand you correctly, you feel the bumpsteer in a street height car does not benefit from the RS change in upright mounting points at either the front or the rear.

The conclusion would then be, unless you are going below street height significantly, the RS parts are a waste of time, since the bumpsteer can be solved with Cup parts. correct?

This would actually make a lot of sense, since I would think if the bumpsteer is a real problem with the Cup racing cars they would have the RS parts installed.

BTW, when you say an 8 pound weight reduction for the RS rear parts, is that 4 pounds each upright or are the side frames lighter as well?

Thanks for sharing your great experience with these RS parts.

Z06

What's special with this subframe compared to the original GT3 piece?

NJ-GT

The subframes on your original picture above belong to the GT3 RS/RSR (race car) not the street car. They come from the factory with solid bushings for every attachment to the car's frame, but the best benefit is the elimination of the eccentric holes (our biggest problem with the GT3 alignment).

The 997 GT3 Cup (the two cars from Jon Groom) came with different rear subframes compared to the 996 GT3 Cup (he had two of those as well). The 997 Cup has the eccentric hole eliminated as well.

NJ-GT

Yes, the slot is not parallel to the ground, it goes in an angle, so depending on where you set the toe link and the control arm inner bearing, there will more or less bump steer. You can't use spacers with the stock toe link, but you can with the Cup/RSR ones. The spacers go on the wheel carrier (upright) side, to level the toe bar close to optimum. Thanks to the location of the front and rear control arms (dead center of the wheel), their angle change doesn't create bump steer, just camber changes and for good (towards negative).

There is bump steer at both ends. The RS uprights fix the bump steer at the front axle, but not at the rear axle. There is a 4 lbs unsprung weight saving per rear upright, but no benefit on geometry. For a street GT3, the rear bump steer is easily dialed-out once you install the GT3 Cup toe links, and adjust the angle of the link with the spacers.

Once the rear bump steer is reduced, this car becomes much faster out of turns. Basically, while the stock car goes towards toe-out at the rear end when you hit the gas out of the turn (due to rear compression and toe link stock angle), the adjusted car stays planted and allows more gas and faster exit speeds as a consequence.

The RS uprights are a benefit because of the weight saving, but their geometry improvement can be achieved and optimized much better with alternate parts.

For the front axle, the GT3 Cup rear toe link can be adapted, and with the spacers, the bump steer can be reduced.

I don't have the weight specs for the RS subframes, but they don't look any lighter than the stock street GT3 hollow subframes.

DanH

So if you already own a stock GT3 RS, is there any benefit to changing any of the parts to cup parts for example?

Also what uprights etc does the 997 GT3 RS use?

thusly

As far as 996 suspension world (from best to stock):

GT-3 RSR > GT-3 (with RS uprights, monoballs, links) > GT-3 RS (race) > GT-3 R > GT-3 Cup > GT-3 street