Greg86andahalf

Hi,

As a regular autocross participant, I will be purchasing either a Devek Chrome Molly strut tower brace, or the 928 Specialist's carbon-fiber strut tower brace. But which to choose????

Any BTDT's who wish to chime in with a opinion?

Thanks,
Greg

Jim bailey - 928 International

Select the one that looks best to you because beyond looks not much is happening . The 928 is a double A-arm front suspension not Mc Pherson strut so there is much less side loading being applied to the shock towers than would be true of a 911 for example . It will not make you faster !

Greg86andahalf

Jim,

Thanks for replying. While i have you here, a few
questions please-

Since I have had to straighten my stock brace a few times, is the stock brace trying to buffer more side-loading than it can handle?

Why do so many 928 stock braces bow in the middle?

I assume that autocross increases the side-loading and tendency for the brace to bow in the middle. I would spend the money to prevent this if it is warranted. Thoughts?

Thanks,
Greg

BC

Jim is correct obviously, but I will have to add to what he said with some other info.

Jim's "co-worker", the venerable Mr. Mark Anderson, Racing 928GTS stroker extrordinair has quite a few braces on his car. He has some diagonal braces that are welded to points on the shock towers in the front, that then go diagonally back to the fire wall. He also has a full cage that probably is located in the correct positions. He has a lower brace that goes from the rear cross member to, I think, somewhere ahead of it.

He wouldn't out that weight there if he didn't need it.

Jim bailey - 928 International

The thin original aluminium cross brace is strong in tension (being stretched )but not very strong in compression . I can easy bend one over my knee and have done so . The design of the brackets to which they bolt is also for tension . The work shop manuals are specific that the bar should only be installed with the weight of the car on the wheels "car must stand on its wheels when cross brace is removed or installed" . I believe that few technicians read the manuals ! So yes there is movement but bolting something to the existing brackets in my opinion is not going to do much as it is designed to be strong in tension only . For racing applications (big slick tires , 3 0r 4 times stiffer springs))it probably needs to tie into the actual shock towers not just to a bit of sheet metal near the fenders . The rational behind using strut braces on McPherson strut cars is to limit the change in camber when the towers deflect . The double a arm suspension of the 928 puts all thoses loads on the "frame " rails the shock towers are supporting the weight of the car but have nothing to do with maintaining the camber of the wheels .

WallyP

If you put big sticky tires on the car and corner at high G-forces, weight transfer will increase the spring loading on the outside tower - and lower it on the inside tower. Net loads on the cross brace wouldn't go up too much.

Jim bailey - 928 International

Brendan , although the 928 chassis is much stiffer than the older 911 at some point you exceed the stiffness of the chassis and instead of springs compressing and shock absorbers dampening the rebound the body flexes and becomes a spring . Install a full roll cage and the weakest part is the portion in front of the cage which becomes the spring . If you want to see the chassis flex jack the car up with a jack under the front lower a-arm mount then put a jack stand under the forward jack point and lower the car. Now start lifting again with the jack and see how much you must lift the front end after you encounter resistance BEFORE the car raises off the jack stand .

Greg86andahalf

I have always re-installed the cross brace with the car on the ground with it's weight on the tires. It just makes sense.

I suppose the general consensus is to not go with a more durable brace. Cool. More money for other projects.

Thanks for the opinions, everyone.

Greg

Normy

Here's a good modification to the cross brace Greg: I found myself leaning upon it all the time to look at various parts of the engine. Often times, the car was hot and so was the crossbrace...burning my hand. Ouch~

The Normy [silly?] solution? Get some gray pipe insulation from Home Depot and put a section around the crossbrace. I secured it with tie wraps, so it is on fairly well and almost looks stock, since it is the same color as the hood insulation. It can be easily removed, and is a LOT more comfortable on the hands.

N!