luseboy Posted October 13, 2011 Share Posted October 13, 2011 Hey, So I'm working on my 240z and today an idea popped into my head. I remember when I was way into modding my MINI, I had seen people talking about filling different chassis pieces with urethane foam to stiffen them. Apparently it makes a "noticeable" difference. Well in my research I've read that the rocker panels are what hold the chasis together front to back. Assuming this is true, what about filling them with foam? there's plenty of holes inside the car to fill them sufficently. Seems to me it would add a lot of stiffness to the car.... I have read about different other chassis stiffening methods... but they all seem too obtrusive for a street-driven car. This one would be totaly stealth once i put in an interior. My only concern is rust and if i ever have to weld anything to the panels (heard of people scrapping shells because they couldn't fix them after the foam was in there). Any other things that could pose a problem? Am I just being an idiot? seems a little too good to be true if it really does make a difference... Anyways looking forward to what everyone thinks Quote Link to comment Share on other sites More sharing options...
72 SBC 240Z Posted October 13, 2011 Share Posted October 13, 2011 Seems like a good idea to me, I would assume that so long as you seek and destroy any existing rust and coat the inside of the rocker really well with a decent primer then the foam would be fine. Later on down the road though I would keep an eye on it because if moisture was to get in there then I bet the foam would make things worse by holding it in. Quote Link to comment Share on other sites More sharing options...
johnc Posted October 13, 2011 Share Posted October 13, 2011 Dumb idea. It won't add any appreciable strength because the rockers are the strongest part of the chassis already. That foam is also difficult to install correctly - you must completely clean the inside of the rockers and make sure they are dirt and rust free, not just covered over with POR15 or primer. And, if you ever have to repair the rockers, you're screwed. You can't weld on any panel that has foam behind it. Quote Link to comment Share on other sites More sharing options...
luseboy Posted October 14, 2011 Author Share Posted October 14, 2011 Dumb idea. It won't add any appreciable strength because the rockers are the strongest part of the chassis already. That foam is also difficult to install correctly - you must completely clean the inside of the rockers and make sure they are dirt and rust free, not just covered over with POR15 or primer. And, if you ever have to repair the rockers, you're screwed. You can't weld on any panel that has foam behind it. very good points! I guess I see now how since the rocker panel is already the stiffest part, it wouldn't make sense to focus on stiffening it. And in thinking... not being able to repair the rocker panels means having to scrap a complete chasis should something go wrong with them. Not probable that anything would go wrong.. but you never know. And that's too much of a downside to have to possibly scrap a classic car that are becoming fairly rare... so this makes me not want to do it, just for fear of ruining a great chassis. Quote Link to comment Share on other sites More sharing options...
David GArcia Posted October 20, 2011 Share Posted October 20, 2011 If i had an extra z laying around I would try to foam the rockers. Its actually not a bad idea. Alot of other countries besided this one are acutallu using that methond instead of using roll cages. Quote Link to comment Share on other sites More sharing options...
seattlejester Posted October 20, 2011 Share Posted October 20, 2011 Sorry, I'm gonna have to agree it's not a great idea. One of the PO's did fill my rockers, all it did was help trap moisture, generate more rust, and make quite a flurry of a mess when I was cutting out the panels, and to replace the doglegs I had to scrape all the foam (that hadn't deteriorated) out, and when welding I would see this visibly thick cloud from the residue I couldn't get to. Unless you seal every hole and ensure no moisture, it will make a giant mess and thin the panels from the inside (any opening will allow condensation). Quote Link to comment Share on other sites More sharing options...
Leon Posted October 20, 2011 Share Posted October 20, 2011 If i had an extra z laying around I would try to foam the rockers. Its actually not a bad idea. Alot of other countries besided this one are acutallu using that methond instead of using roll cages. I'll third that this is a bad idea for the reasons mentioned. BTW, foam in your rockers won't help you in a rollover... Quote Link to comment Share on other sites More sharing options...
luseboy Posted October 21, 2011 Author Share Posted October 21, 2011 I should never have started this thread... It was a stupid idea. If it was a more common, less cool car, I'd do it. But these cars are just too damn cool and are getting on the rare side. Good thing I never did it... found a rust hole on the top of my driver's rocker panel today. Turns out it wasn't just surface rust! Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 21, 2011 Share Posted October 21, 2011 "Alot of other countries besided this one are acutallu using that methond instead of using roll cages. " I'll call B.S. on this one, show me the country or at least reference the FIA specification that allows this. Total load of crap! Quote Link to comment Share on other sites More sharing options...
luseboy Posted October 21, 2011 Author Share Posted October 21, 2011 I can maybe see people using them for chassis stiffening instead of roll cages. but safety-wise? hell no. I think foaming makes sense on some cars, but I would never do it to a car I loved, nor would I do it to a car I planned to drive for very long. It would only make sense for some sort of low budget race series where you use some crap car and only need it to hold up to the one season. Then I'd do it. But not for safety reasons, purely for chassis stiffening. It does make sense though. In chemistry class last year, we focused on the beak of a toucan for a day ( I know this sounds very obscure, just wait), which works on a very similar set up. Basically in order for the toucan to be able to hold its head up, that huge beak has to be light. but in order for it to break into nut shells for it's food, the beak has to be strong. So they have a thin layer of bone-like structure covering an interior of an intricate cartiledge "foam" structure. Just the same as a frame rail of thin sheet metal housing an interior of foam. Makes sense to me. But a beak doesn't go through the constant stress of a car chassis, and it doesn't have worries of rusting through! If anyone ever foams any rails on an s30, I'll be very , because it will basically completely ruin the chassis unless it is done perfectly. Quote Link to comment Share on other sites More sharing options...
zero Posted October 21, 2011 Share Posted October 21, 2011 (edited) Yeah, the theory of making a structure stronger with a stiff foam is solid. Look at bone or foam sandwiched composites. It's just that the practicalities of doing it on our cars make it implausible. Also there may be more to gain by more securely tying the rockers into the other structures of the car than there is by strengthening the rockers themselves Edited October 21, 2011 by zero Quote Link to comment Share on other sites More sharing options...
johnc Posted October 21, 2011 Share Posted October 21, 2011 Alot of other countries besided this one are acutallu using that methond instead of using roll cages. In full composite construction, yes but its not the foam we're talking about here. On production steel chassis vehicles, no. Quote Link to comment Share on other sites More sharing options...
rossman Posted October 21, 2011 Share Posted October 21, 2011 Do I need to break out the structures book to show that adding soft material in the middle of a steel beam doesn't do squat but add mass? Quote Link to comment Share on other sites More sharing options...
zero Posted October 21, 2011 Share Posted October 21, 2011 (edited) Foam doesn't necessarily mean soft, just that it has hollows. There are some extremely rigid foams out there. And, yes, from a basic solid-mech analysis, adding a relatively low strength material to the center of a structure doesn't add much strength. Where it truly makes a difference is when the load gets closer to the buckle point of the structure. The foam can allow a structure to maintain its designed form longer, allowing the steel to do it's work more effectively Here's an interesting link to some testing. I know that it's sponsored by a foam manufacturer, so as with anything, take the numbers with a grain of salt. But if nothing else, you can see how different the failure modes are in the pictures. http://elib.dlr.de/65654/1/Materialien_des_Karosseriebaus_07_04_10.pdf Again, not appropriate for our cars, but not an idea without merit in other uses. Edited October 21, 2011 by zero Quote Link to comment Share on other sites More sharing options...
texis30O Posted October 21, 2011 Share Posted October 21, 2011 For some reason I think the original poster was going to go buy a case of "great stuff" foam from Home depot........not the good stuff By the way don't put Armor All on your tire treads either.................. Quote Link to comment Share on other sites More sharing options...
rags Posted October 21, 2011 Share Posted October 21, 2011 Funny I had never heard of doing this before this thread and now I have a car that I'm working on that has been foamed everywhere! Rockers, front frame rails, inside fiberglass bumpers to name a few places. Quote Link to comment Share on other sites More sharing options...
zero Posted October 21, 2011 Share Posted October 21, 2011 Yeah, I found an alarming amount of "great stuff" in my 72. Inside the doglegs, in the fenders. They had to have something to lay the fiberglass up against... Quote Link to comment Share on other sites More sharing options...
rags Posted October 21, 2011 Share Posted October 21, 2011 No need to worry about that with the new old car, Will Quote Link to comment Share on other sites More sharing options...
rossman Posted October 21, 2011 Share Posted October 21, 2011 Foam doesn't necessarily mean soft, just that it has hollows. There are some extremely rigid foams out there. Show me some polyurethane foam that has a Young's modulus higher than steel. And, yes, from a basic solid-mech analysis, adding a relatively low strength material to the center of a structure doesn't add much strength. Where it truly makes a difference is when the load gets closer to the buckle point of the structure. The foam can allow a structure to maintain its designed form longer, allowing the steel to do it's work more effectively Here's an interesting link to some testing. I know that it's sponsored by a foam manufacturer, so as with anything, take the numbers with a grain of salt. But if nothing else, you can see how different the failure modes are in the pictures. http://elib.dlr.de/65654/1/Materialien_des_Karosseriebaus_07_04_10.pdf Again, not appropriate for our cars, but not an idea without merit in other uses. Nobody's talking about a crash scenario here. We're talking about stiffening up a beam prior to buckling. Quote Link to comment Share on other sites More sharing options...
zero Posted October 21, 2011 Share Posted October 21, 2011 Show me some polyurethane foam that has a Young's modulus higher than steel. I didn't mean to imply there was one, just that there was stuff much better than the "great stuff" some are picturing here Nobody's talking about a crash scenario here. We're talking about stiffening up a beam prior to buckling. I understand that, and I thought I covered that in the post. Sorry if that wasn't clear. Just thought that the ACTUAL benefit of foam filling might be relevant to the discussion too, especially considering the talk of cages and rollovers. Quote Link to comment Share on other sites More sharing options...
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