72 911 3.6 conversion RSR Suspension setup

[CJMRSR]

I am building a 1972 with a 993 3.6 non vario ram with a 915 that has undergone 73 RSR bodywork surgery. EB motorsport RSR front, rear bumper and decklid in fibreglass.

I am looking for a suspension setup up that will predominately be for road use and the odd track day. I would describe the desired setup as an agressive street setup.

I will be doing some european touring in the car aswell from the UK, so I need something compliant enough for several hours in the car.

Current suspension spec I have in my head, which i need to finalise this coming week.

- Torsion bar 22 / 30 ( The 30 on the rear is for the heavier 3.6 and to prevent squat )
- 22mm Adjustable sway bars front and rear. RSR elephant racing
- Adjustable rear spring plate
- Poly/bronze bushing
- HD bilstein front / sport bilstein rear valved to suit
- Raise front spindle height as lowering below euro spec
- Turbo tie roads / bumper steer mod
- Front strut brace RSR welded in

- Front wheels are Genuine Porsche 15x9 fuchs +3 offset on Michelin 18/60
- Rear wheels are EB motorsport 15x11 fuchs -27 on Michelin 26/61

- 930 brakes front and rear

- Genuine RS seats, which I have found are pretty comfy.

- half roll cage in back minus cross brace

Appreciate any feedback from someone with a similar setup.

I currently use an NA1 NSX as my fun weekend and touring car, which has an aggressive lowered street setup but of course is mid engined. I would describe it as lazy steering and pretty neutral when it comes to understeer/oversteer. Hoping for similar characteristics in the 911.

Thanks in advance for feedback.

[Bill Verburg]

Originally Posted by CJMRSR

I am building a 1972 with a 993 3.6 non vario ram with a 915 that has undergone 73 RSR bodywork surgery. EB motorsport RSR front, rear bumper and decklid in fibreglass.

I am looking for a suspension setup up that will predominately be for road use and the odd track day. I would describe the desired setup as an agressive street setup.

I will be doing some european touring in the car aswell from the UK, so I need something compliant enough for several hours in the car.

Current suspension spec I have in my head, which i need to finalise this coming week.

- Torsion bar 22 / 30 ( The 30 on the rear is for the heavier 3.6 and to prevent squat )
- 22mm Adjustable sway bars front and rear. RSR elephant racing
- Adjustable rear spring plate
- Poly/bronze bushing
- HD bilstein front / sport bilstein rear valved to suit
- Raise front spindle height as lowering below euro spec
- Turbo tie roads / bumper steer mod
- Front strut brace RSR welded in

- Front wheels are Genuine Porsche 15x9 fuchs +3 offset on Michelin 18/60
- Rear wheels are EB motorsport 15x11 fuchs -27 on Michelin 26/61

- 930 brakes front and rear

- Genuine RS seats, which I have found are pretty comfy.

- half roll cage in back minus cross brace

Appreciate any feedback from someone with a similar setup.

I currently use an NA1 NSX as my fun weekend and touring car, which has an aggressive lowered street setup but of course is mid engined. I would describe it as lazy steering and pretty neutral when it comes to understeer/oversteer. Hoping for similar characteristics in the 911.

Thanks in advance for feedback.

This shows the effects of various t-bar sets



For street i like 20/26 w/ stock sways and custom valved Bilsteins, for my track 993 i use wheel rates way bigger than anything attainable w/ t-bars alone.

if I was doing it again i look at 2 way MCS as they come std w/ a digressive valve stack and you can fine tune the curves as well. These will also add ~40#s to the above wheel rates, If you got the remote canister versions the addition to wheel rates would vary be be even greater.

note that you tires set up gas already added quite a bit of understeer to the car, you will likely want to compensate w/ the t-bars by choosing a larger value in the last 2 columns above, the adjustable 22/22 sways will help here as well.

I wouldn't use poly bronze on a street car , more because they are a maintenance issue, all rubber particular if you can get harder sport rubber bushes is perfectly fine.

[nickelplated5s]

Bill, pick some rear shocks for my 67! I have only found 3 options. Currently Bilstein that I might be able to have rebuilt. 20/26 T's I believe, adjustable plates & sway's. Rear end is my next project and I'll stay with rubber bushings there. I actually went with a smaller front sway but I'm not sporting a 3.6 in back either.

[CJMRSR]

Thanks Bill, thats super helpful. The MCS look great but I already got the bilsteins.

That chart is very helpful if I am reading it correctly for a 22/30 torsion bar setup it would be 52% less understeer?

I have looked into the poly bronze and I didn't realise the increased maintenance. I will be going with rubber as per your recommendation.

[mradovan]

You may want to consider Tractive. I just put it on my SC that will evenetual have a 3.6 VRAM. They are in the Netherlands. I bought my setup from Smart Racing Products. Craig Watkins has been answering all my technical questions. He was the team engineer for Flying Lizard Motorsports. If you get Excellence magazine you should look for articles by Johannes van Overbeek. He has written a few articles about the virtues of semi active suspension for exactly your application. He doesn't mention Tractive by name but that is what he is driving.

I have no feedback about Tractive because I haven't actually driven the car but I trust Craig and I know it is going to be amazing. Life happens and my car project has been on hold. I am so close to doing a shake down. It may happen is the next few weeks.

[Bill Verburg]

Originally Posted by CJMRSR

Thanks Bill, thats super helpful. The MCS look great but I already got the bilsteins.

That chart is very helpful if I am reading it correctly for a 22/30 torsion bar setup it would be 52% less understeer?

I have looked into the poly bronze and I didn't realise the increased maintenance. I will be going with rubber as per your recommendation.

correct 22/30 is ~52% less under

if you have the Bilsteins already then have a digressive revalve done when the spindles are raised and add the double arm adjustable knuckles, do it front and rear, W/ good digressives double the above wheel rates are streetable. This service used to take about a week turnaround at Bilstein San Diego but I hear that they aren't doing 911/930 shocks any longer. Elephant racing seems to have taken up the slack

[Bill Verburg]

Originally Posted by nickelplated5s

Bill, pick some rear shocks for my 67! I have only found 3 options. Currently Bilstein that I might be able to have rebuilt. 20/26 T's I believe, adjustable plates & sway's. Rear end is my next project and I'll stay with rubber bushings there. I actually went with a smaller front sway but I'm not sporting a 3.6 in back either.

The limiting factor on that car is the wheels and tires it's hard to get more than a 205 in back w/o special wheels.

I'd stay w/ 20/36 and use Bilstein sport all around

[CJMRSR]

The spindle raise height is 19mm max for the 15 inch wheels. Will that be enough? I am in the UK so will need to find someone to do the revalving here. I know you said rubber on the bushings but whats your opinion on the polyeurathane bushes like the powerflex. They have a lifetime warranty by the sounds of it.

[Bill Verburg]

Originally Posted by CJMRSR

The spindle raise height is 19mm max for the 15 inch wheels. Will that be enough?

It'll have to be.

Originally Posted by CJMRSR

I know you said rubber on the bushings but whats your opinion on the polyeurathane bushes like the powerflex. They have a lifetime warranty by the sounds of it.

sport rubber bushes

p/u is awful for sliding applications like suspension connections like poly-bronze it depends on lubrication. Use mono-balls if you need more precise connections than provided by sport rubber. Few do. The beauty of rubber is that there is no external friction that needs to be lubed, hence you get long trouble-free service life.

i use all mono-balls on my track oriented 993 w/ custom digressive Bilsteins and 600/800 springs, It's also ok in relatively smooth street use, the key being the shocks. A buddy has the same suspension except for MC shocks and is even more streetable, largely due to the adjustability.

My 1976 C3 on 20/26 w/Bilstein hd/sport, sport rubber bushes, stock sways 225/255 tires is much better on the street but not as good on a track.

[PeteKz]

CJMRSR: I'll reinforce what Bill said about staying with rubber bushings for a street car. Less noise, vibration, and harshness (NVH), and maintenance-free.

Your '72 probably is a light car, much like my 1973. My strong advice is: Change one thing at a time. Otherwise you will drive yourself nuts trying to figure out which change was responsible for which change in handling. The good news is that the suspension parts can be changed one at a time without re-doing a lot of work, so there's no need to do several things "while you're in there."

Therefore, install the Bilstiens first, then drive the car to get the feel of it. Then switch to 21/27mm T-bars, and keep the stock sway bars. Then drive it for another few months before you opt for stiffer T-bars or sway bars. I think you will be pretty satisfied and won't feel a burning need to make everything stiffer, harsher, and noisier.

[CJMRSR]

Rubber it is.. thanks again Bill

Originally Posted by Bill Verburg

It'll have to be.






sport rubber bushes

p/u is awful for sliding applications like suspension connections like poly-bronze it depends on lubrication. Use mono-balls if you need more precise connections than provided by sport rubber. Few do. The beauty of rubber is that there is no external friction that needs to be lubed, hence you get long trouble-free service life.

i use all mono-balls on my track oriented 993 w/ custom digressive Bilsteins and 600/800 springs, It's also ok in relatively smooth street use, the key being the shocks. A buddy has the same suspension except for MC shocks and is even more streetable, largely due to the adjustability.

My 1976 C3 on 20/26 w/Bilstein hd/sport, sport rubber bushes, stock sways 225/255 tires is much better on the street but not as good on a track.

[CJMRSR]

I'm defos going with the rubber bushings.. I'm going to go with the stiffer setup and pull it back if required. I have adjustable sway bars so no issue their and I can down spec the torsion bars if they cause an issue. I have some turbo torsion bars as a backup if they are too firm a ride. Appreciate your feedback

Originally Posted by PeteKz

CJMRSR: I'll reinforce what Bill said about staying with rubber bushings for a street car. Less noise, vibration, and harshness (NVH), and maintenance-free.

Your '72 probably is a light car, much like my 1973. My strong advice is: Change one thing at a time. Otherwise you will drive yourself nuts trying to figure out which change was responsible for which change in handling. The good news is that the suspension parts can be changed one at a time without re-doing a lot of work, so there's no need to do several things "while you're in there."

Therefore, install the Bilstiens first, then drive the car to get the feel of it. Then switch to 21/27mm T-bars, and keep the stock sway bars. Then drive it for another few months before you opt for stiffer T-bars or sway bars. I think you will be pretty satisfied and won't feel a burning need to make everything stiffer, harsher, and noisier.

[Bill Verburg]

just for comparison purposes, here's a survey of most of the 9111 suspensions setups from '72-89

[3literpwr]

I have 23/31 and adjustable shocks on my '87. To me, its way more understeer prone then the charts above suggest. For road use, it's too stiff and I frankly prefer my 19/27 on my rally car FAR more. I have tuned, build and designed dampers for a large portion of my early career. There is one constant that always seems to happen...people always seem to over spring cars.

[CJMRSR]

Thanks Bill. That is really helpful. I have nailed down my suspension spec.
I am just finalising my brakes setup. I have 930 brake callipers all round and a 930 brake master cylinder. I am tempted to do twin master cylinder pedal box. Do you think its worth it for a fast going road car that might get the odd track day? I take it I cannot use the 930 brake master cylinder with a twin master cylinder pedal box..? Ive read that the pedal spacing can be made less offset with the twin master cylinder pedal box..

[Bill Verburg]

Originally Posted by CJMRSR

Thanks Bill. That is really helpful. I have nailed down my suspension spec.
I am just finalising my brakes setup. I have 930 brake callipers all round and a 930 brake master cylinder. I am tempted to do twin master cylinder pedal box. Do you think its worth it for a fast going road car that might get the odd track day? I take it I cannot use the 930 brake master cylinder with a twin master cylinder pedal box..? Ive read that the pedal spacing can be made less offset with the twin master cylinder pedal box..

w/ 930 brakes a twin master isn't necessary but it would be icing on the cake so to speak.
930s give a brake torque bias of 1.579 and w/ a 23.8mm mc a pedal ratio of 33.105

both are good places to be

stock 72-'83 911 is 1.491 and 41.311 w/o vac. boost or 35.328 w/

I like that bias better but not the pedal ratios


w/ a low stiff car and effective lsd I have 1.426 on both of mine


using a twin master is a juggling context

for 930s w/ 5/8 & 5/8 the bias is the same but pedal goes to 37.18, this ok but a step in the wrong direction, depending on the exact design the bar can change bias from ~2 to ~1.28
using 7/10 and 5/8 bias goes to 1.444 w/ a pedal of 33.66 all good w/ a range of ~1.9 to ~1.1, you'll never likely want anything below 1.45

there

The issue is the lack of fine gradations in available m/c and the interaction w/ pedal ratio.

these are the commonly available m/c
in mm
5/8 15.88
7/10 17.78
3/4 19.05
13/16 20.64
7/8 22.23
15/16 23.81
1 25.40
1 1/8 28.58

Your car will be a hoot, I get such a big grin every time I get mine out

[CJMRSR]

Thanks Again Bill for the info. I have a lot of icing on the cake at the moment so will have to restrain myself a little. I think for its predominant intended use being the road the turbo set up should see me through for a while and its more than enough for my current driving capabilities. If I do a lot more track use and my skills allow I can upgrade in the future.

I cannot wait to drive it. Ive had the cars for 7 years now and only driven it once before it was disassembled for restoration. It should be finished by the end of the year. It always great to hear feedback from people who have done the 3.6 conversion swap in an early chassis. Keeps the motivation to get it finished high..