07-04-2016, 08:03 PM
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CC Member
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Join Date: May 2016
Location: Rural, Kangaroo Island,
SA
Cobra Make, Engine: AC Cobra - ICCARS 001, 4.2LTwin Turbo, AWD, 5 speed tiptronic under construction
Posts: 266
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Not Ranked
Quote:
Originally Posted by SydneyChris
It's a capped 5mm wall section welded all round that's then welded to a 5mm thick disc welded to the rail. The original rail is 4mm wall, 4" dia.
This alone is not sufficient to replace the lost torsional strength but it's within 10%.
The US option is to cut a scallop into the rail from 1/2" to 2" deep then plate over. This solution is about 50% weaker than the initial construction.
The additional side impact rail with uprights and brace to the rear chassis member as well as bracing from an already up sized SHS section from the A pillar to the suspension uprights the whole chassis will be significantly stronger than its original configuration.
There were also a dozen different strengthening measures I'd taken with the original chassis including capping and internally welding the roll cage to the chassis cross rails and adding corner bracing at all overhead junctions.
The proof will be in the beam and torsion tests which according to my engineer will be required for my vehicle, but in short.. Im not just cutting the rail and replacing it with a 6" x 2" RHS.
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Hi Chris, I build Cobra kits in SA and I see a real issue with what you are proposing as the FFR chassis from my understanding only just meets the nominal 6000Nm/Deg of deflection and with the 4" tubular chassis as the base you will find the torsional graph index to be quiet linear from zero deflection through to full deflection at the front of chassis. Therefore by adding in 6" x 2" RHS with a 5mm wall thickness you will be reducing the overall torsional stiffness to the point of non compliance, however more importantly you will be inducing a non linear flexion point on the chassis which can create an area of fatigue, and if you finish the car then set up for the torsional test you will be pulling the car down to repair/modify this back to the way it was. Just food for thought mate, as these are critical changes to your chassis and the potential viability of your project going forward.
Regards
Wil
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Wil Escabache
ICCARS AC Cobra 001 (AWD) U/C
RF 098 GT40 Twin Turbo
ICCARS GT40 - U/C
www.iccars.net
Last edited by ICCARS; 07-04-2016 at 08:14 PM..
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