This morning I was out putting down weed&feed. Its kind of earlier but last year while building walls, regrade, and such I really let it go so I decided to hit the show parts of the lawn now then the whole lawn in a month at normal time. I like to do the fed&feed first thing in the morning when the grass is damp so the stuff sticks....don't know if it actually helps but I've always believed it does so I use the push spreader not to wake the family with the tow spreader making the job slow and boring and giving me an uninterrupted hour to pond Ferrari 308 chassis design and I believe I had an epiphany.....the frames are actually pretty well designed but aren't finished.
Let me explain. If you look at the FSAE frame I posted its a space frame which means it made straight pieces of tubing and EVERY external opening is a triangle, EVERY node is supported in 3 dimensions. This means all the frame member are in tensions or compression with virtually no bending loads, the only exception is the suspension mounts which weren't designed yet when I did the frame and honestly none of us were very sure about how to design it so I used heavy members there to allow freedom to make changes.Even the cockpit opening is a triangle which is important becasue removing just the 2 bars that go over the driver's shoulder to triangulate the cockpit reduced the frames torsional stiffness by a factor 3...so remove those 2 pieced the weight about 2 lbs and you have 1/3 the stiffness you started with. So that is a space frame, wonderful for a race car but clearly worthless for a street car and as a result street cars do not have space frames.
Street cars, and here I mean older street cars that have defined frames all have a version of a ladder frame....2 main rails with cross members. Even most of the new monoque (stressed skin, no real frame) stuff uses ladder like supports. A 308 frame is made this way. With a ladder frame there really is no clever way to keep things in tension/compression so the only way to make it stronger is to just make all the part bigger and heavier....I had a '65 vette and its frame tubes were about double the width of the 308 frame, at least from memory.....the 308 frame is pretty spindly really and ferrari use the exact same frame in the 288GTO (just a 4" stretch in the engine bay) and and the same frame on the F40.....
.....why I wonder? They had to know it was a POS when even a casual observer can look at it say WTF were they thinking? so why?
Racing rules.
Every sanctioning body has cage requirements that mandate, imho, ridiculously heavy cages built in semi-foolish ways. They do that so its easy to tech and hard to screw up so anything you bring that meets the rules is safe. Take a street car, remove nothing structural, add all this new stuff. Everybody needs to follow the rules so it doesn't matter that all the cars are 200-300lbs heavier than they could be, the racing is fair and everyone is safe.
So what does Ferrari, a company who sell street cars to pay for their race program do? They design a nice bottom section of a cage with very little consideration of street performance to make the frame as light as they can get way with knowing old men driving on the street will never notice the flex (this is no doubt also way the stock springs were so soft, to help hide the frame flex issues) and the racers will add a cage, finishing the frame, and have a lighter, faster race car than anyone starting with a car designed as a good street car who then is forced to carry the heavy street frame around the race track.
So they were either incredibly competent or incredibly incompetent. I'm going will they were brilliant.....doesn't help me with my flexi street car issues but it does make a lot of sense. For me, where a cage is not happening there is a bit of a challenge. The front wheels are basically at the front os the passenger compartment so there is little to nothing to be gained up front leaving the engine bay and passenger compartment. with both causing about 1/2 the flex.
The engine bay I can cage. Once the engine is back in I'll design something to bolt on top. On the FSAE frame I reamed the holes and used shoulder bolts on ends of the engine access tubes and that working out pretty well so I'm thinking something along those lines but beefier to deal with the bending loads I didn't have then but will have now.
The passenger compartment.....the only answer is more metal. There is lots of room in the rocker panels but I need to figure out what to do with the cross members....there is a double floor where I lost that steering bolt a couple weeks ago, for sure I can replace that with something quite rigid....I need to model it up and play with it....in my spare time......