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I will take a new bolt and TTA while measuring the torque applied to get a decent estimate of clamp force. From that I can reverse engineer what straight torque can get a similar clamp force without going into plastic deformation.
If not possible with the stock bolts I will be swapping out the bolts to a size that will achieve the factory design of clamp force without damaging the bolt.
One other thing to consider: the back corners have a PAIR of bolts to hold the sway bar. I would be comfortable with reengineering to have the back bolts backed down to normal torque since that will net 15,000# clamp force and double the surface area on the plate.
This may have just gotten stupid simple. Class 12.9 bolts have a higher yield strength than the tensile strength of the 10.9 bolts. You can buy FIFTY of them for less than the SIX if you buy an official BMW bolt.
I'll be doing some measurements and if simply upgrading to class 12.9 will achieve the same clamp force without going to a bigger size you can bet a dozen donuts that I will have a dozen of them in short order.
The only conceivable risk is they could be brittle enough to break vs stretch more but two things about that : whatever maneuver could cause that, a corner of my restriction plate coming loose will be the least of my worries and it will be nowhere near the clamping force maximum I'm betting.
There are also grade 14.9 which are far above and not expensive "each" but the smallest order I found in a quick search is for 1000 quantity.
So: I'm quickly leaning toward get a beefier bolt so I cab achieve the same clamp force of the design spec but not cause any wear on the bolt. With any luck I'll discover that the TTA causes no plastic deformation and I'll be able to report a torque value that approximates the TTA without hitting deformation. I myself would have no problem torquing to 80 N·m vs 90 N·m if the former caused no damage and the latter meant single use on $60 of bolts.
To be continued.
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2011 E70 • N55 (me)
2012 E70 • N63 (wife)
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