It has been brought up before, I know in the MK2 section defiantly search through that forum I know it's a few years old.
did a search but did find anything. Planing to foam my new 83 GTI project, did this before in my 98 2.5rs and my old S13 240SX, short of installing a cage its the best mod for stiffening your chasis, made a HUGE difference.
Anyhow, planing to run 8lb tpf in the rails and 2lb in the pillars again, wanted to see if anyone else had any experience and how much tpf they used all together and any other good spots to hit while I have the carpet out. If anyone is interested I'll add a write up with pics when Im finished as well. thanks!
A4 | 84 | FLHX | PVW 02/09
For the Love of German Cars
I like the idea of using a modern compound to fill voids and add some rigidity, specially if using a compound which does not absorb moisture, which is not hard to find.
Also, weren't there some early westmoreland cars that had some sort of foam in the a pillars and had major rust issues?
Make sure you use a closed cell foam, polyurethane or similar.
I did my complete car, I was scorned on the forums for it though. I foamed everything using varying densities of foam. I received a lot of advice from an automotive engineer that had worked with the foam and gave me advice on densities.
Rocker Panels: 8lbs/cu ft
Rear box around spare tire (Includes rear axle mount box section) 16lbs/cu ft
Front Foot Well: 8lbs/cu ft
Front Frame Horns: 32lbs/cu ft
Front Frame Rail: 8lbs/cu ft
Front Firewall Cross Support: 8lbs/cu ft
A Pillar: 32lb/cu ft
B Pillar:32lb/cu ft
C Pillar: 2 cu/ft
Roof Rails: 32/cu ft (I was't able to do this, never found a good injection system)
I used rubber foam blocks and duct tape to block off a lot of the box sections so that I could fill them with foam from above. Some box sections you will need to drill to get into, such as the rear box section in front of the spare tire. The foam itself is a pain to work with, it sets quickly and is a complete mess. Once it has setup it has to be ground off to remove, even on fresh paint (Ask me how I found that out). I don't have any measurements on the improvement torsionally, I do have some initial torsional strength figures post seam welding and some box section reinforcement we worked out with some weights and a laser level of roughly 700lbs/degree (Which is really weak, cheap modern cars are on the order of 5000+lbs/degree)
I added roughly 45lbs to the car in foam, and total cost was around $350. Doing this completely changed the handling and feel of the car. I run 400lb/in front and 320lb/in rear springs and the car was immensely stiffer and much more prone to having the rear go airborne on bumps.
Due to the added stiffness I expected the car to have more understeer but the opposite occurred. The car moved more towards neutral handling, which makes sense given how weak hatchback rear ends are, the foam had a lot of affect there. The car is also more stable at higher speeds and the turn in is much sharper (And negatively throttle lift oversteer is much harder to catch). Overall the car is the quietest Mk1 I've ever been in, very few rattles but still has plenty of wind noise. For me it was an experiment given everything else I've done to the unibody. Not really something you can do on a race car, a cage will be more effective. But for me as a play car it was worth it.
Anyhow seems like theres a bit of interest so I'll do a write up with pics, just placed to order so prolly the week after next.
so far the areas Im planning on doing are the frame rails, cross floor rail and pillars. (stole this pic from Urogolf's build thread, thanks!) Will probably cap off the side holes and drill into the rails from the top (white dots) its a bit of a shame the rails do not connect to the rear strut towers (white box), ideally you want all four strut towers fully braced together for the best rigidity, well I guess the Mk1 was designed in a time when most engineers had just switched over to calculators from slider rulers
Also the pillars are going to be a bit tricky, the hole back half of the B pillar will have to be capped off (blue section), again this is a place where modern cars are fully boxed in for rigidity and safety. you can do this with a plastic or even cardboard sheet cut to fit and duct taped in though, the foam will follow the path of least resistance as it expands so it doesnt take much to cap it off, even pretty large holes are fine with duct tape as long as theres a place for the foam to go.
These small rails under the car are also a good area to fill. Again, on all new cars these rails run the length of the car specifically for longitudinal rigidity. (sorry, dont remember where I found this pics but damn thats clean!)
Last edited by krinkov; 06-01-2011 at 06:58 PM.
Yes, body shops have a repair procedure that involves removing the panel and grinding out the foam so there's enough space to inject more once the panel is replaced.
Also in the picture above make sure you foam the boxed section which is just in front of the spare tire well, this one is critical for rear stiffness.
The foam can seal rust which they do in marine applications. Two part urethane foam is very similar to automotive paint. It's also used as an adhesive, a la Gorilla glue. You can definitely seal it with paint if that makes you feel more comfortable. Again this is nothing like the stuff you find at home depot. I got some on my control arms and I still haven't been able to chip it off. 16lbs stuff is as hard as pine wood.
Couple things though. you used 32lb foam in the pillars! WHoa!!
I used 8Lb foam and even that dried to the density of wood, 32Lb must have been like pouring concrete! And were you able to do injection on the 8 and 16Lb or were those just poured? I usually do 2lb injection and pour the 8lb. As for the weights I got from the Chrysler research paper, I used to have the .pdf but the link disappeared, I'll post it if anyone wants a good read. They determined that 8Lb foam was the best balance of weight/rigidity, the heavier they tried just had diminishing returns since the 8lb is stiff as hell. though if the heavier stuff worked well for you thats fine too. As long as you dont mind the small weight penalty theres really no downside to how stiff you make your chassis, the stiffer the better.
Also as for foaming the front frame rails/horns, you only need to add rigidity between the four corners, adding rigidity to any of the structure ahead of the front axle or behind the rear axle only adds weight. This is why most roll cages, even the really elaborate ones, only connect to the four strut towers. Also the structure in front ahead of the front axle is usually designed to be a crumple zone so its usually best to leave that alone.
Sorry not pointing that out to be a dick, Im sure you just did this all at the same time, just wanted to add that to this thread for anyone that reads this later and wants to foam their car, its important to know where your time money and weight added is best spent. Heres two books that have been around for years that everyone that wants to tune their suspension should own and reference frequently
thanks again for the info, I might pick your brain a bit more once all the foam gets here
Basically what I was told is the larger the cavity cross section the lower the density of the foam. Since the rockers have a fairly large cross section the force is distributed so 8lbs is great. The 32lbs is probably over kill but for high stress areas and small cavities under 1 sq inch cross section it works great. I should note on the frame horns I only poured in about 4 inches of the 32lb stuff and the rest filled up with 8lbs. Also take out your control arm bolts and grease them good and put them back in before foaming. Another lesson learned, mine are now permanently attached.
To push stuff into the pillars I built a pressure vessel out of a 1 gallon bucket with a lid. Put an air fitting on it and a 3/8" tube out, about 3-5psi was enough to push it out. You have to work fast and clean it up with acetone before it sets. Temperature is key I got the best results around 65 degrees outside. I tried once at 80 degrees and it set before I even had it completely stirred and foamed like crazy.
Last edited by Fast2.0L; 06-01-2011 at 08:28 PM.
Foam is shipped, should be here midweek, hopefully I can free up next weekend for the foamin' as usual i bought way too much so if anyone here in the sf bay area wants to get in on it we can have a foam party (that doesnt sound good)
anyhow while we wait heres a very informative, though agonizingly boring video from TAP plastics about their 2Lb closed cell TPF. And also their flexible open cell foam if anyone wants to make their own home made nerf balls.
Last edited by krinkov; 06-06-2011 at 03:25 AM.