Questions on my upcoming chassi modifications and cage setup?

[J. Fast]

So you're saying the body itself is structural? Ahh, I see what you're describing. The actual design method you're referring to is called Monocoque. Yes, the rear hatch is monocoque designed as it's dependant on sheets for its structural rigidity. I'm actually pulling all the sheets to convert from monocoque to spaceframe. Spaceframe is much lighter and relys soley on triangulation to balance the tension and compression of the frame. Essentially, thats what principle caging a body in tubular material is based on.

My main concerns in the rear chassi are the forces exerted on the suspension mounts, impact zones, and any forces that may come from driveline torque. Once I clean up all the sheet metal I'll triangulate the loads back to the main frame and suspension towers and have much more structural rigidity vs. the OEM monocoque design. As for the driveline torqu that causes twist, our cars are AWD so the force is already proportioned so I'm really no to concerned about it. My thinking is The lighter I get the chassi, lower I move the weight, and smaller I make the CG radius, the faster and stronger the car will be?

[anyonebutme]

I think you missed my main point at the end. PPIHC TT rules stipulate that OVM (original vehicle manufacturer) unit body cars can NOT be converted to spaceframe (body-on-tube). Page 55 of the rulebook. You're already flying in a grey area removing sheets, so I'd be very careful how far you proceed. Removing false floor panels and pieces for cage clearance is one thing that usually is approved, but all it takes is one savvy inspector to DQ you for going just a bit too far. This is why I asked for a rulebook first. If this is a "fun" car that you plan on doing trackdays and such with it, proceed ahead.

[edit]: that steering shaft support I was looking for, but I haven't found the actual manufacturer yet, cage guy hasn't e-mailed me back yet:



FYI, that blue thing is a quickener. If you plan on actually doing hillclimbs or something other than typical circuit, might be a wise investment depending on driving style.

Oh, and the CG circle term your looking for is "polar moment". Centralization of mass.

[edit2, something MB doesn't know how to do]: Found options for shaft support:

http://pitstopusa.com/c-133240-steer...-brackets.html

http://www.hrpworld.com/index.cfm?tp...action=product

[J. Fast]

I see the gray area but how I'm reading the rules, I'm not modifying the Unibody at all. The whole skin which is "the unibody" and floor pan is still OEM and un modified. The main frame will also remain. And it says I can modify or alter panels to accomodate for cage space?

I sent an email off this morning to check on the rule to see if it's okay that I proceed with removing the layers. I'll let you know what PPIHC says. Thanks for the heads up!

[J. Fast]

Today’s progress, I took it all the way down to the skin on one side.







For good measure (if anyone was wondering if I know what the hell I'm doing)...







Yes, the frame is still absolutely straight. This process is slow and requires a shit ton of trig and geometry and double checking every time I remove a panel.


Tomorrow I have the day off due to weather so I'm guessing I'll be done pulling everything. With any luck I'll be finished with seam welding and grinding by next Friday.

I still have the other side to do but you can pretty much see where I'm going with this. Believe it or not, it's actually very fun!

[Alex3000gt]

This is one heck of an undertaking.

Good luck!

[anyonebutme]

Looks great! BTW, are you going to a fuel cell?

[J. Fast]

Looks great! BTW, are you going to a fuel cell?

Possibly, it depends on cost vs. weight, what I find when I tip the car over , and a few other factors. I'll be forced into making that decision soon enough though.

Right now I'm just working on getting the car really really light.

[niterydr]

You will want a fuel cell. The 20 gallon tank + shield + factory fill crap is NOT light.