69T - suspension tinkering

[gridgway]

My 69T has as far as I know reasonable stock suspension with no anti roll bars (i know the latter for a fact!).

Am I right in thinking standard torsion bars are 18.8mm and 23mm? It has koni front shocks and bilstein rears.

It's an E spec engine which pulls well and makes you want to chuck it about! It's lovely and light, but has a lot of body roll, which is kind of ok, but gets a bit tedious after a while.

All I'm thinking of doing is trying just to take some of the roll out. So I thought anti-roll bars. But at the rear that looks quite ghastly as I think it has to pick up on the spring plates, having standard trailing arms.

But the options are limited...torsion bars, shocks, anti-roll bars.

Any words of wisdom/experience out there?

Cheers
Graham

[fetuhoe]

Tricky to decide on the best approach as this will really depend on the specific problem you need to resolve.

The Torsion Bar sizes are 18.8 and 23mm and you could increase the roll stiffness by increasing their diameter but as the spring rate will interact with the damper rate this may not provide the ideal result.

The dampers rates front and rear will also interact and have in influence on transient weight transfer and if the bump/rebound settings are mismatched could result in a car that becomes 'twitchy' in terms of steering or 'tail happy' depending on the direction of the mismatch.

It seems likely that you may have a car that just lacks sufficient roll stiffness in a steady state and that the body roll occurs in long sweeping corners and dampers are unlikely to solve the problem.

Changing torsion bars will increase roll stiffness but will also impact on ride quality and various other aspects of the cars handling and again may not provide the 'best' result.

Fitting anti-roll bars as the first stage in the process of improving handling and reducing roll is most likely to be the best way forward.

Early SWB cars had 13mm front sway bars and these would be quite easy to fit as a starting point. Rear sway bars were an option.

In the 1972 'Sports Purposes' booklet suggested that a 1970 MY 911T used in sporting events should fitted with 14mm diameter for both front and rear.

A more fully developed 911S would have used stiffer bars but for a road car this may be a good solution.

To fit front bars is quite easy but you will need to weld 'tabs' to the front A Arms and the cost of lever arms and drop links can be high unless you can find good used parts.

You will also need to weld rear sway bar mounting consoles to the body shell and the location of these consoles is straightforward. To connect the sway bar to the trailing arms the best way to fit them is to weld in the correct ball pins. You can find systems that mount the sway bar to the spring plate but we are not keen on this arrangement as it tends to be over constrained.

The Ball Pins are still available from Porsche but ideally should be fitted using a jig, which we can help with.

Once you have the basics organised you can then fine tune with damper settings.

[Jesse]

Chris, I must give you the biggest thank for your thourogh explanations.

Many forums have lost their "tech" gurus so your posts are very, very important to the community.

I´m pretty sure that most others feel the same way!

Jesse

[911hillclimber]

My 73T had no roll bars from the factory, nice ride, but then I hill climbed it and found it wanting. (roll and much more)
I did all the work Chris says above and used 2.7 RS roll bars, stock torsion bars. This was all DIY for me so easy!

I changed the engine from a 2.4E/S to a heavier 3.2 and alloy box and put 3 litre Turbo rear torsion bars in, same anti roll bars, and custom valve'd Bilstein dampers which came via Bob Watson.
Alloy banana arms went in too, I still have the steel 73 arm with welded adaptors (not the correct ball ends) for the custom drop links I made (adjustable)

Car has a great ride, great dynamics, and will be at Fenn Lane /Chris's place in Jan 18 for a geo set-up.

Hiil climb, 60 mph slight adverse camber. 3.2 as described above, fresh Bob Watson full geo set-up.

[gridgway]

So that's interesting Graham, were your bars 18.8(F) and 23(R)? That's probably what my 69 has and it rolls a lot. Sounds like yours didn't have that on the road?

And as Chris says bars seems to be the way to reduce roll, but it's a reasonably expensive mod. 4 arms to take off and weld, the locating brackets welded on, then front and rear bar kits. Then reassembly.

Hmmm
Graham

[911hillclimber]

Graham, I'll measure mine tomorrow and post back.
My 911 is in bits in prep for Chris.
I made and welded the U tabs for the front wishbones, bought the 2.7 bar and through the body mounts and new bushes.
The rear was harder.
Bought the mounting brackets from an autojumble ( the much missed Husband Crawley one) with the bracing web and mig welded them on so the bar would miss the gearbox mount, there is not much clearance, so you need to be careful.
The mod to the banana arms in steel was easy, machined some long pivots and drilled, welded those in place.

To all this is the kit once made by Weiltmeister in the USA where the bars are all bolt on!
It looks a bit Micky mouse to me, hence going the factory route.
Don't think they are made now...Keith Sueme might have them on El Chucho, not sure.

Bob was magician on suspension and did 3 set ups on my car, road only, hill climb, serious hill climbs, but all 3 ran great on the road.
Since a specialist had a go at the car 4 years ago, they screwed the lot up I had to re-do it all myself the day after. The job they did was simply crap.

I trust Chris to get the car back to a Bob W level, the car is now a little weekend car unless the BIVA change that!
Bob spent a lot of time getting the corner weights right at the time with just my weight in the car as I was hill climbing it then.
A hill climb is simply a country lane run fast as possible knowing nobody is coming the other way, so a good set up for that works well on the road IMHO.

[911hillclimber]

Anti roll bar diameters are 18mm Fr and Rr Graham on my car.

[gridgway]

Thanks Graham, but the rear isn't 18mm I guess?

[911hillclimber]

Yes, both are 18mm dia.

I even measured them with a digital vernier, so must be right, and just re-checked.
Must admit, I thought the front was smaller, but both 18mm.

They came to me via Bob many many years ago when I started hillclimbs seriously, car was just so planted when he had set it up even with the lardy 3.2 in the rear.
It was sharper with the 2.4E/S mag alloy cases drivetrain, but I needed more power/torque, so the 3.2 went in after 3 years of the 2.4.

[davep]

It has koni front shocks and bilstein rears.

Whist the advice has been excellent, I'm not sure that mis-matching the shocks is a good idea. On one car I have all Koni's and on the other, all Bilstein. The gas-pressure shocks will modify the behaviour a little I would think.
Some front A-arms do have the U-tabs for the anti-roll bars, so it may be worth checking first.

[gridgway]

Yes, both are 18mm dia.

Astonishing! That's about 1/3 the stiffness of the 24.1 I think was 'stock'. No idea how that can work unless I have got the wrong end of the stick.

Whist the advice has been excellent, I'm not sure that mis-matching the shocks is a good idea.

Yes, I would agree. Although, it seems to work apart from the body roll. Could that be caused by the different shocks front and back?

[Gary71]

The bars are only the same stiffness if the lever arms and the point of action on the wheel is the same.

They might be the same diameter but if one acts through a short lever right at the wheel it will be more effective than the same bar acting through a long lever and connected a long way up the wishbone towards the inner pivot.

[gridgway]

Is it possible to connect the torsion bars in different ways on the rear of a 911 to have that effect?

[Gary71]

No idea! Certainly the aftermarket versions tend to have a number of fixing points for the drop links.

I know the attachment method changed post ‘78 at the rear but I don’t know about the position on the trailing arm.

The front bar changed massively to the underbody rather than through body. I’d imagine the lever arm changed at the same time.

[gridgway]

ahh, I've got it now, I am on completely the wrong track . I was talking about torsion bars. The other Graham as I have just worked out it talking about arb's as are you! I'll just creep back in my hole and feel stoopid for a while!