It’s time to let my little project out of the bag. My goal is to build a street legal ‘go-cart’ with some of the best suspension equipment on the market, to be used in weekend runs through the mountains and other fun drives. Another criteria was to maintain the stock 930 look, so the only exterior mods will be a DP style front spoiler to allow for the center cooler. As much as I would like to track this car, my current job and family commitments just don’t allow it. Getting to this point in the project was a big enough battle.
The parts:
1. Moton Motorsport double adjustable coilovers
2. ERP 935 front suspension
3. ERP 935 rear spring plates
4. SRP front and rear sway bars
5. Elephant Bump steer kit
6. Wevo front monoballs and plates
7. Elephant rear sealed monoballs
8. Wevo rear sway bar mounts
9. Wevo transmission mounts (already have the engine mounts)
10. Full Brembo GTP Brake setup
11. All new wheel bearings and seals
12. Custom fabricated tub reinforcing
13. Custom Stainless x-braces and crossbraces
14. Elephant 935 center duct with Setrab STD-272 cooler and hoses
15. Zuffenhaus 9x17 and 11x17 fuchs with a 255/315 Nitto NT-05 tire setup (if the wheels ever get here?)
I got the start of the suspension setup below and added a few more items:
http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/482791-brand-new-complete-erp-moton-935-coilover-suspension-911-930-8500-a.html
I fully realize that a suspension such as this isn’t going to be maintenance free on the street, but most of the wear parts are pretty easy to replace. All the heim ends are typical American thread and are fairly cheap in comparison to other Porsche parts. If I have to replace them every year, so be it.
What started the whole thing:
http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/525417-started-off-good-day-but.html
Once I got the pan replaced, the question now became how to reinforce the tub for street use, while not adding unnecessary weight. It’s well known that the 930 tub doesn’t have the stiffness of a 964 or 993 tub, and wasn’t designed for coilovers, but the question was how could I make it better? I’m a structural engineer by profession and used my experience to look at all the loads (at least my interpretation of the loads) being applied the stock tub and what paths they take. In addition, I spoke to several people behind the scenes and got all the opinions I could. Also, plenty of late night bench racing, looking at ‘what if’? And yes, a fully cross-braced cage, tied into the suspension points would be the best, but this a street car.
So here’s the issues I came up with:
1. The 930 tub wasn’t designed for coilovers. Need to get the load path from the strut tops back to the original locations, and reinforce those areas for stiffness.
2. Eliminating the rubber in the suspension will increase the dynamic load into the suspension mount points. Need to reinforce the mount points against fatigue cracks over time.
3. The front 935 suspension, by design, puts much more load on the front mount points than the stock A-arms. Especially under braking. Need to add welds, reinforcement and bracing to the front parts of the tub.
4. Once you add bracing, you’re now moving load to another location that wasn’t designed for it, so that will have to be reinforced.
I’m sure there are a million ways to approach this, right or wrong, the following pics are what I came up with. I’ll try to update as I progress, but that’s pretty slow at this point.
First the popular 'Alarcon' plates. These plates really are ingenious, they not only reinforce the flimsy area around the sway bar mount, they also tie the double layer strut tower into the wheelhouse and all the way to the steering tunnel. If you look close you can see where I drilled holes and puddle welded through both layers of steel at all the panel joints, further tying all body panels together at the strut towers. I cut the center hole 1/2" larger in diameter than the SRP mount and carefully TIG welded around it. These plates look pretty simple, but took plenty of forming with hammers and a sand bag to fit the wheelhouse contours. One tip.....fit and weld the perimeters of the plate first, install the mounts and bend the base metal to square up the mounts and get the smoothest movement of the sway bar before welding around the mount. They don't bend too easily afterwards.