Rancie

Gentlemen

I have a 1990 C2 with KW Clubsport suspension and top mounts. Sway bars are factory RS front and rear with adapted (shortened ) drop links. Engine mounts are RS. On track, the car drives well but there is a little too much slack in the suspension and not enough control for geometry adjustment. To tighten things up and give me more control, I am fitting the fllowing items;

1. Elephant racing sport bushes for front control arm and rear trailing arms

2. Tarett rose jointed adjustable sping plates

I am aware that there is a law of diminshing returns in this situation but what other essential upgrades would you also recommend?

The car is used on both the road and track so I would like to keep a reasonable balance with that in mind.

Thanks in advance

anto1150

I suggest a couple of these!

-nick

"not enough control for geometry adjustment. To tighten things up and give me more control"

What exactly are you lacking in geo adjustment? What feels not tight? Other mods? Tire selection? Do the clubsport top mounts have camber adjustment? What are you running for geo and what are you aiming for? Are all the usual suspension items fresh- ball joints, tie rod inner/outer, wheel bearings?

Bushings definitely tighten up the response. Engine and trans mounts help too, but nvh will rise for road use. There are poly steering rack bushings that I would fit in every 964 which help a little.

Rancie

Thank you. Yes, already ordered!

Rancie

Hi Nick

My geo is quite a sharp set up approx -3deg negative camber, RS ride height -20mm with a little addtional rake etc.. Tyres are Cup 2's. Top mounts are Monoball KW adjustable. Limiting Camber adjustment is the damper body fouling on the inner wing. Ball joints, tie rods and wheel bearings all new.

The toe adjustment on the rear is compromised by the standard set up hence the Tarett adjustable spring mounts. The geometry is being compromised under load on the circuit as the standard bushes deform. That will be improved by the Elephant sport bushes. I wondered if there was anything else that i should be looking at? I come to this from a circuit driving standpoint and am used to rose jointed/shperical joint set ups but my 964 is both a road and track car and i wish to retain an element of compliance and originality.

Thank you for the tip regarding the steering rack bushing. i'll definately look at that.

Here is some in car footage of the car on it's standard bushing. After the session, the loaded tyres were showing wear signs well beyond the shoulder of the side wall

You Tube

-nick

Ah, that gives better context!

This is a dual street/track car? I wouldn't expect the street manners would be so great at RS-20. The maximum that the front control arms can pivot before they contact the unibody is RS-75mm. The clubsports would be made to hit the bump stops well before that. So you may only have 30mm or so of compression travel, which is a pretty rough ride. Something to check out, but none of that would greatly effect responsiveness on the track.

I don't have experience with Cup2's but your front camber sounds in the ballpark for sticky tires. Have you experimented with pressures, or pyrometer readings across the tread?

When you say rear toe is compromised, are you not able to get it into spec? Or you're measuring significant toe changes with side load? At RS-20 the rear will toe-in more quickly under compression by design. The more the rear is compressed, the more rapidly it will toe-in.

I wonder how much of what you're feeling could be isolated to the steering? The C2 inner tie rods are softer than the RS/C4 versions, which in turn are softer than the stock 993 versions. Changing to a spherical inner tie could help sharpen the steering. I'm working on that in my C4 at the moment. Most manufactures use spherical bearing inner tie rods with no additional rubber isolation. Possibly, Lexus SC400 inners are the correct length...

That's about all that I have for ideas. Hope it helps!

Spyerx

look at my build thread :-)

what spring rates are you running?
If you want control, you remove all rubber from the suspension, steering, get 993 uprights for proper front Geo, ensure you have a proper alignment/balance

Even with all monoball everything, with a compromise spring rate and shocks adjusted as such the ride is quite compliant. You do get some NVH, and the steering can be very sharp, but that's due to the agressive camber/setup on my car.

But for me, it's quite tolerable.

Goughary

Definitely.

Also. Forget about lowering the car super low...you get no benefit out of lowering the car too low. Stick with RS +10mm front and rear, and work out the geometry from there. If you want lower, you have to change the front uprights and do a lot more work, and then you still have marginal benefit, so unless you are racing an identical car in a class where the specs keep you all close and you need to worry about 100ths in a lap time...not worth it.

Nick- I'll be interested to hear what you come up with for a spherical solution to the inner tie rods. I like that idea. I have an old set of C4 inners I was looking to do maybe a hard poly bush in those and see what that would do...

Good thread- let's see what comes of it...

Bill Verburg

If going to Rose joints in back you may want them in the front as well

-nick

Personally, I wouldn't use rose/monoball joints anyplace that isn't completely sealed from the elements on a dual purpose car.

I agree with Goughary on ride height. I'm at RS and I definitely wouldn't go any lower for my multi-purpose car. I think that the Cup cars were RS-25mm, so you're running on the extreme end.

Consider RS engine mounts and the Function First trans mount insert. One of the easier options to try out. You can easily sell them off if you don't like the added nvh. They will make the whole car feel noticeably sharper.

Bill Verburg

Not 993, for low you will want 993RS wheel carriers +993RS outer tie rod ends

just for comparison
stock front RoW 964 ride height is 165+/-10mmn, 155mm would be at the low limit for stock, 258mm+/-10 in back
stock front 964Rs ride height is 125+/-5mm, 120mm would be at the low limit, 223mm +/-5 in back

w/ essentially the same front suspension
993RoW is 154mm+/10, these use al. wheel carriers w/ pretty much the same long arm geometry as the steel 964 versions. When the car is lowered the steering geometry gets whacked

993RS is 124mm+/-10, these use al. wheel carriers w/ short arm geometry that restores steering geometry on lowered cars, these were really designed for the 993Cup, 993GT2 and 993RSR which run 94-95mm front

lowering the car to 94mm w/ all mono-ball connections which eliminate rear steering effects is very beneficial to track handling, much less so for street use.

for a dual purpose car, sport rubber in front and rear is a very nice compromise, the RS stiffened the rear bushes by adding 2x 3mm washers on either end of the rubber bush, you can do that or perhaps find sport rubber bushes(maybe both)

Goughary

Bill- can you explain this further or show a diagram?

Ty

Bill Verburg

#3 2x 3mm washers

Spyerx

@bill it's what I meant the 993 Evo uprights and the erp tie rods and in era with bump steer correction.

Anyone in SoCal that wants to ride in my setup is welcome. It's niiice. Good dual purpose setup. Ok maybe a little stiff for the layman :-)

Rancie

Thank you for the replies Gentlemen. Some good information.

I arrived at the set up after a few days testing. I wanted to keep the car as stock as possible so have tried to achieve a chasis balance without changing the front uprights to the better 993 Evo units. I run the car low with a little more rake than usual and on rlatively stiff springs which minimise front suspension travel. I drive the car on it's nose like a contmporary cup car. The set up works well, it has a nice balance but it does rely on help from the diff during the braking phase. Currently I have a standard factory Limited slip unit which is adequate but only just. Soon i'll be fitting a Guards GT tranmissions unit with a little extra preload which will make things a little easier to balance during a trail. Braking is 993 turbo fronts and 993C2 rears without any bias adjustment so it's heavily front biased. I know that this would not be everyone's taste but it suits my driving style. Pace wise the car is quick by race standards and it still has electric windows and aircon fitted so I'm happy with that.

So basically i'm happy with the set up but when the car is at 10/10ths on the circuit there is a vaigueness about it common to any reasonably heavy car with rubberised bushing. Although I can drive a balance into the car, I can feel it floating as the bushing loads and distorts. Changing the engine mounts to RS units has made a decent difference. The standard mounts were hopeless and promoted oversteer on exit as the engine rotated on the loaded mount. The other problem that I am getting is accuracy of rear toe adjustment which my race shop are struggling with, which is why I've purchased the Tarett spring plates.

Great info re; the washers on the bushes. I've checked the Elephant items and they apprear to accommodate this concept which is encouraging. I'll definately look at the steering rack bushing also.

Thank you again for your input. This forum is extremely helpful