Harebrained idea about chassis stiffening, Just a thought for the engineering types Options

[jamara]

Well, I am not engineer, but I’ve got a harebrained idea for reinforcing the longs of the 914. I want to run it by you more experienced engineering types out there.

Theory:

1. Engman’s kit strategically places steel on the longs and lower firewall. Why? Because two pieces of sheet steel welded face to face are stronger than one by itself.

2. However, two pieces of sheet steel, separated and firmly affixed to a lighter weight material (fiber, honeycomb, thermopolymer, etc), is exponentially stronger than two pieces of steel welded together. Here is a site with more than you ever wanted to know about composite sandwich materials. The section at the bottom under "Core Materials for Sandwich Structures" is what you want. Pics at the bottom are a good illustration of the principle.

http://www.mdacomposites.org/mda/psgbridge..._materials.html

3. A similar technology is being used on modern cars during their production. They put polyurethane pour foam into the A and B pillars, as well as the rockers of new cars. It deadens sound and really makes the chassis rigid. Here is a link to a “tuner” car that this was done to. Look under “Foam filling the chassis”

http://www.sportcompactcarweb.com/projectc...rt_5/index.html

4. In terms of applying this to the 914 longs (putting pour foam in them), RUST is the deal killer. The longs on my car are “rust free” but still have some surface rust inside. With solid material in them to trap moisture, this could become a major problem. Also, the longs are fairly voluminous and so cost for foam and the resulting weight is another issue.

So, here is my proposed solution.

(IMG:http://www.fc.biola.edu/~james.calley/long_modification.jpg)

This would involve welding ½” x ½” ½” tube steel to the inner long in a lattice configuration. Then as with the engman kit, preformed sheet steel (18g) would be rosette welded to the ½” tube steel pieces, to the floor pan, and to the upper door sill seam where the inner and outer long meet. This would leave a ½” gap between the inner long and the “skin” The lower firewall would simply have steel added like the Engman kit, or perhaps this sandwich method could be used.

Now the good part….

8lb per cubic foot polyurethane foam could be mixed and poured into the ½” gap on the inner long. There would need to be evacuation points for the urethane foam so that when it expands it doesn't blow the welds.

Advantages:

1. Only 2.7 lbs extra weight in polyurethane given about 1/3rd cubic foot for both sides
2. Since we are dealing with the face of the inner long, it could be cleaned, phosphatized, Por-15’ed, gold plated, whatever, before everything is buttoned up. No rust issues.
3. Extreme rigidity since sandwich materials like this apparently behave like monolithic (solid) structures . In other words, it would be like having a huge 1/4" thick Engman kit with a fraction of the weight.
4. Only ½” invading the cabin area, as opposed to a roll cage.

Problems:

Relocation of the E-brake handle to the center console and possibly the back pad not fitting quite right. Also, the speaker grills in the front would need modifying. The ½” is not much but could cause problems here. Plus, my proposed design is to attach the top of the “skin” to the ½” lip at the top of the door sill where the inner and outer long are spot welded together. This is the area where the lower, inner door seal slips on and is held in place. Therefore, the trim piece that goes here would not fit without modification and the seal would need to be modified as well. Last thing, the seat belt bolt holes might need to be moved to the floor pan.

Anyway, this is just an idea, so don’t anyone start foaming at the mouth over it. (I will discretely NOT add a link to the 914world forum topic on the subject of pour foam in the longs, where someone started typing obscenities and colorful metaphors over the matter.) What do you think…?

[JPB]

I like the idea of making the car stiffer but it is by far better to keep the car original. The purpose of making the car stiffer depends on application. If the car is gone structuarly then, one has to make a decision on which way one needs to go. This foam stuff is not cheap. Going original is not cheap either when one consideres the price if replacement longs and such. Its probably cheaper still to just get a good tub and use the other car as a donor which proves a point in that it far better to get a complete and drivable car for 4K than get a beater to drop some serious cash into. If you want race car parts, its also good to look for a race car with everything you want in your car since these are usually well maintained as well as being good tubs.

If I were to start over again, and I will, I would make a cool rolecage that goes at the role bar, ties to the e-belt bolts, runs horisontal to the rear shocks area via the fire wall, welds to a 1/8"X 3"X4" angle iron sill on top of the longs, run another pipe over that sill about 6" above it tied with stub pipe under it on an angel, at the front of the front door weldes to that 1/8" angel with another vertical stub then runs on to tie to the front wheel wells. I'd put a cross bar at the rear role bar frame and probably another at the dash to tie the two extensions going to the front wheel wells. This will stiffen it up and keep the role bar low and away from site when driving. I would also tie the two front and rear shock towers with cross bars. At the sill tube and the rear role bar, there would be another tube going at an angel next to the seat but not in the way when one enters the car. (IMG:style_emoticons/default/beerchug.gif)