Bernie930

Better turn that shock 180 deg otherwise it will cut the CV boot. Also get the proper front and rear uprights to take advantage of the subframes

pete95zhn

Closest point has about 5cm of air between.

IMO not cost effective enough.

pete95zhn

Rest of the parts installed. Next issue is dialing all in. I'm planning to lower the car with wheels on stands so I can set all heights before taking it to corner alignment.

pete95zhn

Proto parts are changed to anodized, all joints have protective rubbers, too long front springs swapped to correct ones and the suspension is dialed in...it's aligned and corned weighed. Kussmaul settings with one exception, front camber's 3.1 deg. Ride height's 105 / 125 mm. From the pics it doesn't look like that, body's level with the ground just like CUP cars.
Despite much stiffer springs than before street ride's not harsh, there's just some more noise.
Based on the first track outing it's now very balanced and very sharp, rear end doesn't move on it's own on the suspension anymore.

fbirch

Very nice work. Beautiful car

pete95zhn

^^^Thanks!

rbahr

Hi Pete,

Great project... I suspect (but won't bet money) that the uprights have more impact than the cross members.

I have not yet updated stuff yet - but there was a fitment issue with the rear sway bar and the motor with the side members as high as they are - I will post pictures. The rear sway bar mounting points were lowered

The new uprights require some creativity with the ABS/Speed sensor wiring...

I want to get my car down to the Cup car ride height : 86 mm / 107 mm but I have a fitment issue with my existing shocks - can you tell me the length of the cup car shock body?

I am also struggling with the 'correct' spring rates - my 'calculations' have me ~600/900 f/r which is low - been talking to the folks at Hypercoil - like they know something about springs :-)

What rates are you using?

TIA

Ray

pete95zhn

Ray,

I got the inspiration to machine those subframes from your thread. Plus I found a pic of rear subframe from '02 996GT3 RS's Tech Handbook, it's 1:1 to mine.

It would be nice to see side-by-side pics of GT3 and CUP uprights for pick-up point's difference. I do have a feeling that early CUPs share GT3 mk1's uprights. Actually that's not a feeling....I just checked it from aforementioned RS's Parts Catalogue. FIA-homologated version (2001 regulations) has the same front upright than a mk1&2 GT3 (99934115791). ACO-homologated version's part# is different (...1579D).
GT3. GT3 mk2 M004's part number is ...15792, which is IIRC same part than late CUP's.
At rear numbers are: 99633111106 (GT3 mk1&2 = early CUP?), ...11190 (GT3 mk2 M004 =late CUP?), ...1119A (GT3RS)
I should get me a 996 CUP's PET & WSM....anyone?

I thought I had the same problem, but then I loosened transmission's and engines bolts that attach them to chassis and grabbed a crowbar. =) No sway bar fitment problem when the engine is full aft.

GT3 M004 has ABS, so the option should be there, it's just how to dig it out.

Body's 220mm (vs GT3's 230mm'ish), but the piston's just 120mm (vs 170mm'ish). Measured from the middle of bottom bolt hole to body's top and from the top of the body to the first cut on piston.
For the current ride height (and piston calculated to mid cylinder with static load) I have a 30mm spacer between shock's top mount and the body. With a GT3 shock I wouldn't need that, or for CUP's ride height I'd just ditch the spacer. IMO you'd need shorter shocks.
For front I don't have GT3's measurements.

My spring rates are quite moderate, F: 80 N/mm (456), R: 120 N/mm (685). I may switch to stiffer ones depending the this season's experiences. Some use 1100/1300...
CUPs run, depending on MY's, F:240-260 N/mm, F:260 N/mm.
GT3 RS has F:280-345 N/mm, R: 317-375 N/mm

BTW, the GT3 RS I'm referring to is this car:

rbahr

That was exactly what I did - I had someone do some work on the car who did not like that solution so they effectively lowered the sway bar mounting...

I got it to work without changing the wiring - just could not use the original tie downs for the wiring - I also need to make allowance for brake cooling...

FYI:

2005 RSR

The front coil spring has a four-step adjustment range, the corresponding spring rates are listed in the table below:

Step 1 Step 2 Step 3 Step 4
282 N/mm 293 N/mm 317 N/mm 345 N/mm

The standard rear coil spring has a four-step adjustment range, the corresponding spring rates are listed in the table below:

Step 1 Step 2 Step 3 Step 4
282 N/mm 293 N/mm 317 N/mm 345 N/mm

An optional rear spring is available; the corresponding spring rates are listed in the table below:
Step 1 Step 2 Step 3 Step 4

317 N/mm 333 N/mm 352 N/mm 375 N/mm

Ride height

Ride height - ACO 55 mm 65 mm (Rake = 10mm)
Ride height - FIA 83 108 (Rake = 25mm)

2004 Cup

Main Springs 100/240/60 (240 N/mm) 130/260/60 (260 N/mm)
Helper Springs 75/60/43 60/60/50

Ride height 86 mm 107 mm (Rake = 21mm)


WRT the spring rates ( I know this has been discussed before) but with a square or equal front to rear spring rate and a numerically smaller motion ratio in the rear, the rear effective rear spring rate is LESS than the front... go figure... (or please explain cuz I don't get it...) perhaps that depend more on the sway bar in the rear to control roll (what a concept...) Getting late and I am punchy - but if someone could clear this up I would be enormously grateful...

Ray

pete95zhn

Ray,

2002 RSR's ride height was 82-112 mm (rake 30mm), springs the same that you posted. I got a note about those rakes which I hadn't thought at all, namely tire height. Race cars use tires of different height at F & R axles and that affect the rake too. Street cars' tire height tends to be more or less the same.

Spring rate, wheel rate & and motion rate...I'll need more beer... Cheers!

rbahr

Thanks Pete,

Seems like they changed the ride height for 2002 to 2005 - Check the 'reference material' I sent you.

Thanks

Ray

outline

They did, but the 04/05 RSR isn't using the same wheel carriers as the 02 RS. The RS has a 30mm rake to compensate for the extra reduction in side carrier height. The RSR used the later style wheel carriers and the reduced side carrier which changes things again and thus rake differs. Be careful reading too much into the RS/RSR stuff when applying to your street cars. Its a whole other ball game with aero/power/body etc. Remember the ACO ride heights are measured from points on the flat floor so aren't directly comparable.

BTW, ref the cup ride heights. You don't have the same wheel tub space as the motorsport cars so may come across issues. If you keep a low profile rear you may be able to get away with it though I expect you will still be camber restricted regardless. Theres potential contact issues on the inside of the outer fender wall with regular levels of camber once you get low but as you add camber to avoid these you run out of room on the inner tub.

rbahr

Thanks for the feedback - Do you happen to know how low I can go with the ride height and the street tub?

I have been chatting with a few folks about camber - question is 'how much is really necessary'? RSR (front) calls for ~ -4 deg, I am suspecting that -3.0 / -3.5 is plenty (depending on tire)

Ray

outline

That I do not know. I was going to suggest asking the spec 996 people if they know but it may be as easy to stick a jack on the subframe, pull the rear shocks off and drop the car and look how far down you can get before it starts hitting things. Its the rear where you have less wheel tub space as you start getting down. The shorter tyre will help for sure but how much I don't know.
Camber is a tyre issue. Temp readings will tell you when its right.

pete95zhn

Data from Saturday:

F: Camber 3.1 deg / Temps: L 69-72-75 R 76-71-67 (Celsicius)
R: Camber 2.4 deg / Temps: L 62-67-72 R 74-66-59

MPSC, +20C OAT. IMO, and compared to the "Care and Feeding" -guide of Michelin those are on the low side. But they're IR measured after a hot lap. What's strange rears are cooler than fronts....with my power and torque. OTH the track is quite slow, puts the strain on fronts. Datalog shows 1.498 G of vector accel at best.

BUT the suspension really works! I managed to drop almost two secs from my previous best time on a 3 km track.