Home  |  Forums  |  914 Info  |  Blogs
 
914World.com - The fastest growing online 914 community!
 
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG. This site is not affiliated with Porsche in any way.
Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners.
 

Welcome Guest ( Log In | Register )

> Harebrained idea about chassis stiffening, Just a thought for the engineering types
jamara
post Nov 14 2007, 03:51 PM
Post #1


Member
**

Group: Members
Posts: 63
Joined: 27-February 06
From: LA, CA
Member No.: 5,645



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…?
User is offlineProfile CardPM
Go to the top of the page
+Quote Post

Posts in this topic
jamara   Harebrained idea about chassis stiffening   Nov 14 2007, 03:51 PM
jd74914   Welding in those square pipes would take a lot of ...   Nov 14 2007, 04:11 PM
jamara   Welding in those square pipes would take a lot of...   Nov 14 2007, 06:13 PM
davep   8lb density pour foam? Are we talking polyurethane...   Nov 14 2007, 06:38 PM
jamara   8lb density pour foam? Are we talking polyurethan...   Nov 14 2007, 07:14 PM
kwales   As an engineer and a car repairer, the foam idea m...   Nov 14 2007, 07:43 PM
jd74914   As an engineer and a car repairer, the foam idea ...   Nov 14 2007, 11:18 PM
Aaron Cox   As an engineer and a car repairer, the foam idea...   Nov 15 2007, 10:52 AM
byndbad914   The foam does work as a stiffener. That's pro...   Nov 15 2007, 11:47 AM
jd74914   The foam does work as a stiffener. That's pr...   Nov 15 2007, 01:40 PM
jamara   The foam does work as a stiffener. That's pr...   Nov 15 2007, 04:52 PM
drive-ability   jamara, I like the fact your thinking outside th...   Nov 14 2007, 09:50 PM
byndbad914   I would hack the inside of the longs and the floor...   Nov 14 2007, 10:45 PM
andys   I would hack the inside of the longs and the floo...   Nov 15 2007, 11:41 AM
Borderline   My idea would be to work on the outside similar to...   Nov 14 2007, 11:20 PM
davep   Free rise density of the foam is less than 1 lb pe...   Nov 15 2007, 11:58 AM
jamara   Free rise density of the foam is less than 1 lb p...   Nov 15 2007, 03:58 PM
davep   You guys might be correct that some of the foams m...   Nov 15 2007, 04:37 PM
kwales   I've built aluminum and foam core structures f...   Nov 15 2007, 07:41 PM
jamara   I've built aluminum and foam core structures ...   Nov 16 2007, 04:16 PM
Jeff Hail   I've built aluminum and foam core structures...   Nov 16 2007, 08:16 PM
Brando   I second the carbon fiber idea. The only way I co...   Nov 15 2007, 09:02 PM
byndbad914   jamara - I am familiar with using poly in cavities...   Nov 15 2007, 11:03 PM
Jeff Hail   Something that needs to be brought up. If a chassi...   Nov 16 2007, 01:04 AM
kwales   As one guy that did aircraft structures taught me,...   Nov 16 2007, 07:57 PM
woobn8r   If the "ENGMAN" kit is "double bagg...   Nov 17 2007, 05:04 PM
JPB   I like the idea of making the car stiffer but it i...   Nov 18 2007, 10:59 AM


Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



- Lo-Fi Version Time is now: 2nd July 2025 - 02:02 PM