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Tyson Schmidt Tyson Schmidt is offline
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Join Date: Nov 2001
Location: Burbank, CA
Posts: 4,463
Randy, I really don't think you'd ever notice the rear shock tower reinforcements. They're really there for strength and long-term durability. I know many guys who have rear coil-overs with no reinforcement whatsoever, with 550# springs or more, who've been tracking their cars extensively with no problems.
The truth is, it's the stiff shocks that cause the super high loads that are transmitted into the shock towers, not the springs. And the rear shock towers do not carry any forces from lateral G's, just jounce and rebound. It's the rear torque tube that takes all the cornering forces transmitted into the spring plates and control arms. That tube's structural integrity is extremely important.

As far as torsional stiffness, it would take a jig and some method of twisting the chassis with a given lever arm by a certain amount of weight, and movement measured with a dial gauge to determine torsional stiffness. Not really something that anyone is going to bother measuring. I don't know if Porsche has ever published these numbers for a stock 911 coupe.

The cage definitely helps. The shock tower braces aren't really for torsional stiffness. (Like mentioned above) But I tied the center tunnel in with the torque tube, and added diagonal braces between the inner rockers and the center tunnel, which no doubt help as well. But their primary function is for stiffening up the rear suspension pick-up points to minimize rear suspension geometry changes during high G-loads.

The triangular rear shock tower braces versus the tube tying them together? Well, that all depends on how stiff the spring/shock combo is, how much grip the car has, how much torque the drivetrain is putting to the ground, and how heavy the car is. We really aren't in that realm yet. I don't think Jack is ever planning on installing racing slicks, and a 750 HP turbo engine into his car. But that could change!
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'69 911E coupe' 2.7E MFI (retired 911-Spec racer)
'72 911T Targa (Formerly "Scruffy")
2004 GT3
Old 01-27-2004, 11:23 PM
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