aarc240 Posted October 28, 2011 Share Posted October 28, 2011 A bit of "real world" experience. I have a 'special' built on a 1937 English Ford chassis that utilises the best high density foam infill I can get hold of. Because of the design, this car has largish side pods made of thin gauge aluminum attached to a light tube steel structure. The side pods are epoxied and riveted at all joints and at the attachment areas so there is absolutely no ingress of moisture. This is one case where foam filling DOES make a very significant difference to stiffness without adding a risk of moisture retention. On the other hand, our 240z navigation trials car doesn't use foam fill inside any of the factory cavities. Instead, after rebuilding the body shell the original factory panel joints throughout were reworked with a spot welder so that the spot welds have gaps no wider than the diameter of the spot welds themselves. Sure, a similar result could be achieved with a MIG or TIG, but at the expense of added weight. Finally all 'closed' members were thoroughly soaked inside with a phosphoric acid & PVA mixture which not only kills all surface rust but also leaves a moisture resistant skin. Why do one car one way and the other a totally different way? I made up some test box sections from wrecked 2+2's and loaded them until they collapsed. The ones with foam fill were significantly better than the factory stock ones. The "spot welder gone mad" examples were nearly as good. So, why add a potential problem with foam in there when it wasn't really needed? btw, the trials car has a one piece aluminum under tray with HD foam between it and the floor, but that was made by oiling the floor so the foam would release. The floor continues to be oiled with a 140 weight to prevent rust. There are places for HD foam, they're just not inside steel sections unless corrosion protection can be guaranteed. Quote Link to comment Share on other sites More sharing options...
zero Posted October 28, 2011 Share Posted October 28, 2011 (edited) Tony, Obviously there is no such FIA ruling, and the guy who said that hasn't posted in over a week. No one else is claiming that. Manufacturers are using it to meet FMVSS roof crush standards though. I made up some test box sections from wrecked 2+2's and loaded them until they collapsed. The ones with foam fill were significantly better than the factory stock ones. The "spot welder gone mad" examples were nearly as good. There are places for HD foam, they're just not inside steel sections unless corrosion protection can be guaranteed. Exactly the sort of information I was looking for. Awesome. I was thinking of doing that with my scrap 240 shell when i cut it up. Thanks! Also, here's another interesting read on foam in an existing unibody and it's effect on stiffness. http://www.mwsmotorsports.com/z32/foam/1999-01-1785.pdf Edited October 28, 2011 by zero Quote Link to comment Share on other sites More sharing options...
aarc240 Posted October 29, 2011 Share Posted October 29, 2011 (edited) Thanks for posting that link, it's provided confirmation of a couple of theories I've had for a while. It highlights why the shape of the Z has a significant impact on the structural rigidity of the car. The joints shown in that paper which affect the Z are 1, 3, 5/6 and 7. Joint 8 isn't a problem due to the large load bearing area created at the rear of the hollow beam along the top of the inner fender. Joints 1 & 3 are similarly relatively bulky with attendant stiffness. Joints 5 & 6 are actually combined at the top of the rear pillar and along the side of the hatch so there's a lot of support there too. All of these benefit from a dose of "spot weld fever" to such an extent that the torsional beam strength of the body is measurably increased. Supporting our lightened 240 on three corners and loading the fourth confirmed my belief at the time of build. Prior to extra spot welding, either unsupported rear corner deflected 7mm with 250kg load and either front corner an average of 9mm. There was a small amount of radial twist measurable diagonally through the cabin space but this didn't exceed 2mm in any direction. Interestingly, while there was a small amount of rotation in the door openings, at no time did it become enough to prevent hanging and closing the doors which tells me that the sill rail beam is pretty sturdy. For an un-modified body that's actually pretty darn good compared to many "modern" cars! After hours of spot welding (about 6 altogether) the same tests were carried out. The rear deflection came down to less than 2mm and the front to less than 5mm. To my mind that was a good result for the effort expended. That leaves joint 7 and this IS a problem area as can be testified by anyone who loses a windshield during a gravel rally or trial. The entire front of the roof shakes sideways as well as exhibiting vertical vibration sufficiently to require the side windows be wound down so they don't get smashed too! The extra spot welds obviously do help but equally obvious is that the windscreen is a structural necessity which is not too surprising given the cross sectional area of the A pillars. So, it would seem that more research into corrosion proofing joint 7 internally is in order so that a HD foam can be used to stiffen the joint. A trials car is particularly prone to moisture in the roof structure due to damp and muddy gear, hot floor, demister going flat out and freezing cold outside so it's a good test bed. edit: You're right that there's no FIA rule, and equally correct that OEM's are using it for crush reasons. Edited October 29, 2011 by aarc240 Quote Link to comment Share on other sites More sharing options...
Tony D Posted November 2, 2011 Share Posted November 2, 2011 OEM's are using it as an integral design of the vehicle not as a substitute for a proper cage. The reason I made the statement I did was he IMPLIED that vehicles thussly constructed are somehow exempted from having a cage. THEY ARE NOT. Structural foam used as an integral part of a vehicle's design improves Governmentally-Mandated crashworthiness. That requirement is a FAR CRY from competition-sanctioning-body approval to "eliminate cages" or whatever foolishness he put forth initially. It's governmentally acceptable... But not to an extent that it exempts them from caging in competition, or from chassis reinforcement for competition use at this present time. I think our mate from Australia brings forth the most relevant and pertinent example of what 'naysayers' have contended all along: conventional preparation of the chassis with proper weldments of the seams will perform on the S30 to a practical equivalent of adding the foam, but without impeding any future repairs required. If your goal is to make something that is basically a "Throwaway" vehicle (like the direction today's cars are going) then, BY ALL MEANS, foam the rockers, A & C pillars, hell construct the entire interior out of freeform sculpted foam. But if you want a car that is repairable, best skip it. Quote Link to comment Share on other sites More sharing options...
Tony D Posted November 2, 2011 Share Posted November 2, 2011 "Supporting our lightened 240 on three corners and loading the fourth confirmed my belief at the time of build. Prior to extra spot welding, either unsupported rear corner deflected 7mm with 250kg load and either front corner an average of 9mm. There was a small amount of radial twist measurable diagonally through the cabin space but this didn't exceed 2mm in any direction. Interestingly, while there was a small amount of rotation in the door openings, at no time did it become enough to prevent hanging and closing the doors which tells me that the sill rail beam is pretty sturdy. For an un-modified body that's actually pretty darn good compared to many "modern" cars! After hours of spot welding (about 6 altogether) the same tests were carried out. The rear deflection came down to less than 2mm and the front to less than 5mm." An Engineer can convert that to a torsional stiffness number improvement! "That leaves joint 7 and this IS a problem area as can be testified by anyone who loses a windshield during a gravel rally or trial." Or anybody with enough torque and grip to twist the area because they were foolish enough to build the car for the street without foresight to put in a proper cage! (Hey, I was 23...and was forewarned, having a friend with a V8 Pinto that would pop rear glass on corner exit---out and onto the pavement behind the car! "Hey Jaques, you lost your back window!" ) Quote Link to comment Share on other sites More sharing options...
Tony D Posted November 2, 2011 Share Posted November 2, 2011 One thing that should be noted was that on 'Works' cars, the panel thickness was increased in critical areas to help with the issues aarc240 is mentioning. The Monte Carlo Rally Cars were 'not' your typical off the shelf 240. They had special panels throughout the construction, which differed from the SCCA Practice in the USA of buying a car off the showroom floor and running it that weekend. Those "Works Rally" 240's were the Japanese Equivalent of the 60's NASCAR chassis built at the factory and shipped directly to the teams competing. Yeah, it was a "Stock" car... I've got this bridge in Brooklyn up for sale as well! Quote Link to comment Share on other sites More sharing options...
zero Posted November 2, 2011 Share Posted November 2, 2011 (edited) Tony, I think we're on the same page now. Again, I never said this was a good idea, particularly for our cars. It would render an s30 scrap at the first sign of water or damage. And I certainly would never suggest foam instead of a cage. In fact, I don't think I'd suggest it for much of anything other than a Lemons racer, but it may be perfectly suited for that!(after the cage is installed of course) I just wanted to counter some of the talk that the stiffening properties were COMPLETELY without at least a basis in truth. There are absolutely better ways to stiffen an s30. It turns out it is about the same as spot welding, and I know which option I'd choose! As a mechanical and aerospace engineer with a focus in composites, I knew the mechanisms by which they made composites stronger(deformation resistance, transferring loads to be borne in tension), and I could see those mechanisms acting on a steel box section as well, and I knew of their use in newer cars. That is great info on the works cars. To be honest I had always wondered about that. Even amateur level rally racing can wear out a new, heavy and safe chassis pretty quickly. I was curious how, even with a cage, they managed not to crack those chassis. I kind of love factory backed cheating like that, I'm reminded of the turbo toyotas; wrong, but pretty impressive nonetheless. Edited November 2, 2011 by zero Quote Link to comment Share on other sites More sharing options...
aarc240 Posted November 3, 2011 Share Posted November 3, 2011 (edited) An Engineer can convert that to a torsional stiffness number improvement! Yes, I have that but to most people it's meaningless. they were foolish enough to build the car for the street without foresight to put in a proper cage! Regrettably, this isn't an option in Australia where full cages are outlawed on the street. A half cage is accepted and does help somewhat. Re the "Works" cars and the myths pertaining to them, by 1972 that is exactly what they were, myths. The lightweight panels and thicker frame rails had been banned and to stay competitive the customer cars were JDM HS30L versions with some extra stiffening and a lot of extra welding. In international (ie WRC) rallying the Ford Escort in particular headed in a very different direction by construction and sale of sufficient homologation specials to kill these Japanese upstarts. Way back in '72 I had one of those 'customer cars' bought & supplied for competition use and it really wasn't anything special, just a gutted 240Z with Fairlady badges! Hey, I was 23 then also, but the Pinto was a new-ish model and came with an asthmatic 4 cylinder! Of course, if you were really insane there was supposedly a V6. Thankfully, Ford never produced a right hand drive version so we were never saddled with the things here. Back to the real subject, the only area of the body that is inadequate is that joint 7 simply because there isn't enough attached material within the joint. I'm still pondering that and will have to wait on a couple of 2+2 turrets now undergoing accelerated corrosion testing. They have been treated with two different corrosion proofing regimes so hopefully one will show that it is possible to "shake proof" that part of the body. It's a very different aim to stopping the torque twist imposed by say a 500hp V8. Edited November 3, 2011 by aarc240 Quote Link to comment Share on other sites More sharing options...
Wedge Posted November 21, 2011 Share Posted November 21, 2011 (edited) There was a good thread about this on NICO forums someone did it to their 240sx and noticed a great deal of improvement and rigitity. Their found it http://forums.nicoclub.com/chassis-stiffening-foam-result-part-1-qualitative-result-56k-no-go-t270721.html Edited November 21, 2011 by Wedge Quote Link to comment Share on other sites More sharing options...
seattlejester Posted November 21, 2011 Share Posted November 21, 2011 ^I was a bit disappointed that his conclusion was based on feelings. I'm kind of curious as to the mentality of the use of foam. We found out that epoxy resin soaked core mat would outperform it's counterpart of a similar weight in steel at handling load by measuring angles of deflection at various load points (in tons). <-That was actually a fascinating study as it compared different structures (tubes, square tubes, planks) and the only real downfall is that core mat reinforced carbon fiber was it would delaminate and fracture at it's limit, where steel would bend as long as the force was applied gradually. So wouldn't it be a more beneficial to reinforce areas with long sheets of carbon fiber, or core mat if one is on a budget, and fill the cavity with an epoxy resin? The cavity would be waterproof and significantly stiffer. /rant induced by PO. Quote Link to comment Share on other sites More sharing options...
Wedge Posted November 21, 2011 Share Posted November 21, 2011 Well its not like the test he did could be tested by engineers ... im sorry if my post sounded like if porsche engineers did some test and posted it on the internet...Of course a guy tested it, he felt it was better. It Is up to you to think if you want to try it out on thing for sure it would try it. Dont want to sound pissed but i posted the link as info on foam strenghtning a car. Quote Link to comment Share on other sites More sharing options...
seattlejester Posted November 22, 2011 Share Posted November 22, 2011 Sorry if it seemed harsh, (I hope your not upset, since the comment wasn't directed towards yourself). I felt the thread was on a good track as the basis for the mod was sound and he attempted to do some measurements by measuring the deflection in the door, then he chose to be more entertaining, and then finished it off by saying how it difinitively works with how he felt instead of some sort of data, he provided quite a few anecdotes. I mean a lot of the statements could have come from other factors, like his front brake pads wore down, he added more weight to the vehicle so it's settled more and ironing out the bumps, etc etc. Had a statistics teacher who left an impression on me. Quote Link to comment Share on other sites More sharing options...
johnc Posted November 22, 2011 Share Posted November 22, 2011 I can make a car "feel" stiffer by adding DynaMat to the doors. Had a customer tell me that after he drove his car home from my shop. Quote Link to comment Share on other sites More sharing options...
Wedge Posted November 22, 2011 Share Posted November 22, 2011 Sorry if it seemed harsh, (I hope your not upset, since the comment wasn't directed towards yourself). I felt the thread was on a good track as the basis for the mod was sound and he attempted to do some measurements by measuring the deflection in the door, then he chose to be more entertaining, and then finished it off by saying how it difinitively works with how he felt instead of some sort of data, he provided quite a few anecdotes. I mean a lot of the statements could have come from other factors, like his front brake pads wore down, he added more weight to the vehicle so it's settled more and ironing out the bumps, etc etc. Had a statistics teacher who left an impression on me. No problem, hehe Im just wondering how someone could test the strengthning to give some sort of results or data... Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.