ulrichd

I'll be doing new Bilsteins all around and Turbo tie-rods for my 78SC next weekend. The question is, while I'm down there, is it recommended to upgrade to larger torsion bars if I want a lower ride height (24.5/25). My car is for street driving only (no track), and the lower ride height is just because I think 911s look better that way.

Thanks in advance.

Edward

Hi Ulrich,

You dont have to stiffen your ride just because you're lowering the car. While I would, indeed, recommend that you stiffen mildly, that is merely my preferance, and not at all necessary, especially isince you have no track aspirations.

Should you decide to stiffen mildly, the turbo tbars are a good, mild increment toward more body control. And while everyone has a different definition of "tolerable," I could not imagine any 911 driver who would deem the turbo-size t-bars as too stiff or unacceptable for daily street use. They are also usually easy to find cheap and used as most of us nuts are usually going to much stiffer bars, and thus bypass these altogether (sorry, can't recall their dimensions off the top of my head).

Regardless of tbar choice (even if you stay stock), I'd highly recommend you upgrade to Carrera sway bars (22mm/21mm) --they bolt right in, offer much flatter cornering, and practically no degradation of ride comfort/quality. BTW, IF you decide on swapping t-bars, you should evaluate the condition of your bushings since replacing the bushes later will require another suspension disassembly and alignment. Hope this helps you.

Edward

sww914

If you decide to do bigger swaybars later, I would recommend that you reinforce the rear swaybar mounts while there's no swaybar in place. There is a nice kit for it, but the reinforcements must be welded in, not a hard MIG project, just get everything clean down to bare metal first, and prime and undercoat the welded areas liberally afterwards.
Those stock swaybar mounts break often enough to warrant the preemptive attack in my opinion.

autobonrun

I would hold off for now replacing the torsion bars. First, are you going with Bilstein HD's or Sports all around? I recommend driving the car on a track environment with the new shocks before attacking another part of the suspension. You need to see how the car drives with the new shocks before you make another suspension adjustment in my opinion. If I'm not mistaken, the stock torsion bars on your car are 19mm front and 24 rear. Porsche chose these settings for a certain amount of understeer/oversteer. Until you drive your car in a track environment with the new shocks (and hopefully new tires), you don't know whether you want more or less understeer. You can effect this by changing the 19/24 ratio to another setting, say 21/27. I went with Weltmeister hollow torsion bars when I did my replacement, primarily as a weight reduction. There are several articles out there that describes the relationship between torsion bar diameter, suspension stiffness, oversteer, and understeer.

Second, as the others have said, you do not need stiffer torsion bars to lower the car. You can lower the front using adjustment bolts. Lowering the rear requires you to rotate the torsion plates. If you are going to remove the plates to lower the car, then would be a good time to replace the torsion bars, but it is not required. More importantly at this time, check to see if the rear bushings are flattened out. You can actually inspect them now. Check to see if the rubber at the top is thicker than that at the bottom. If your's are stock they are probably no longer round. I replaced mine with Neatrix bushings. I admit, replacing these bushings was the worst DIY job I've undertaken. Not difficult but tedious and time consuming. However, new bushings all around adds new life to your suspension.

I'd say go slow. You may find you like the factory torsion bar setup.

autobonrun

Here are two good sources of information on torsion bars. As you will see from the equations, torsion bar stiffness is related to the diameter of the bars to the 4th power; so it doesn't take a large increase in diameter to greatly affect the stiffness. And again, you can use the ratios to adjust the understeer and oversteer of the car.

http://www.pelicanparts.com/techarti...rsion_bars.htm

http://www.rennlight.com/cgi-bin/spring.cgi

ulrichd

Thanks guys - I think the step-by-step approach is a good one. I'll do the Bilsteins first and see where that takes me. The pulling of the rear torsion bars to look at the bushings is a must as well. I also have the turbo tie-rod kit on order.

The car currently has original Boges on front (154K miles!) and fairly new Konis in the back, courtesy of the previous owner. To say the handling is entertaining is an understatement.

autobonrun

You don't need to remove the torsion bars themselves to check the bushings. You may be able to see even with the torsion tube covers on. Maximum you need to do is to remove the covers. The first photo is fairly poor but it is a shot of my old bushings. On your car, you will be able to see if the rubber on top is thicker than that on the bottom. If you don't have metal touching metal, you have some time. If it's flatter on the bottom but the metal is still not touching, you don't have to do it right away but put it on your to-do list. The bottom photo is the refinished units.

Are you going Bilstein Sports or HDs?

ulrichd

I am doing Bilstein HDs and maybe up to the Turbo swaybars later.

jaydubya

If you are replacing the shocks and are going to lower the car, cut the bump stops to shorten them a bit. The following article assumes you have Bilstein strut housings (green):

http://www.smartracingproducts.com/p...hock_front.pdf

theiceman

The boges have spacers under the fender, I though they could be removed when upgrading to give more shock travel when the car is lowered. ( I took mine out )

ulrichd

I have Boge struts on my 78. Is there a spacer as well?

jaydubya

If you guys are talking about the big honkin metal washer, yeah get rid of that when you lower the car. I was talking about the rubber (foam?) bump stops.

theiceman

Yeah ulrich it will fall out when you take your shocks out. I think it was put in to meet US bumper height requirements of the day or something.

Anyway Ulrich when you are doing your shocks:

You can do them by only undoing the strut nut on top and pushing down through fender
line your fender edge with painters mask covered by duct tape
I used a impact hammer to undo the strut cap nut, but others may use large channel locks
If you are consiering your brake lines this is the time as they could be stressed swinging the strut from under the fender
suck oil out of strut housing before dropping in new strut.

Put it all back together.

Took me about 3 hours to do both with the car jacked up already and i really took my time.

ulrichd

Thanks for the great info Iceman. What did you use to suck the old oil out of the strut?

911pcars

Unless the roads you drive are very rough, I think you'll find heavier torsion bars don't create as rough a ride as the combination of Bilstein HD/Sports and large sway bars - this, according to many owners. In fact, some owners with aftermarket sway bars and stock torsion bars have tried to increase roll resistance by adjusting the drop links closer to the bar. This overstresses the area and can cause the sheet metal (front bar) to tear. Better to take advantage of larger t-bars to control weight transfer than rely solely on sway bars.

For better handling (subjective, I know), I'd recommend installing heavier t-bars before or in conjunction with heavier sway bars. This is independent of whether the ride height stays stock or is lower. I too thought heavier t-bars would provide too rough of a ride. They don't. They firm up the ride a little, and that's in an early pre-SC 911. Carreras carry more weight and, IMHO, can use more t-bar than essentially the same size bar used since the 911's inception (okay, the rears are +1mm bigger).

Sherwood
http://members.rennlist.org/911pcars