Foam Stiffning the Chassis

[Maeda]

Ok so in a class I have we were doing urethane foam mold construction... and applying this to car-dorkdom, I found this stuff online that stiffens the chassis a whole lot... Anybody do this before? I hear the 4AG guys like to do this...

So i'm going to do it! but does anybody have any insights?

[BadMoJo]

It does help alot from what i have heard.... BUT there is a few drawbacks, like that fact that if you ever get into a crash the chassis will not soak the impact up as well, it will transfer the impact to YOU. So you could possibly get hurt more in a crash..

[Maeda]

Is this something you just thought of? What about stiffening only the cabin area(the part thats NOT supposed to absorb impact) and stay out of the crumple zones?

I think this stuff coupled with a minor rollcage for roll over protection is just what im looking for in terms of stiffness.

[andrave]

sport compact car did it on a project car a while ago...
not that they did a very good job of writing it up....
not saying that means anything...
it being in sport compact car doesn't say much at all, except that whatever they do will be duplicated and parked 3 blocks down within 6 months...

[S13Grl]

Foam-Filling the Chassis
In any high-performance car, it is impossible to make the chassis too stiff. The stiffer the chassis, the higher its natural frequency, making the energy imparted to it by bumps less likely to excite the body's structure. A stiffer chassis enables the use of stiffer springs and shocks without hurting the ride. This is because a stiff, non-flexing chassis transfers more force into the suspension where it can be dissipated by the springs and shocks instead of transferring the force to the occupants. A stiff chassis is also more responsive to roll rate tuning for balancing understeer and oversteer. This is one of the reasons why automotive engineers are continually investigating ways to stiffen chassis without adding weight.

In a final bit of reengineering to stiffen the body, we injected the chassis with catalyzed rigid structural polyurethane foam. Structural foam, in the 2 lb per cubic foot density that we used, can stiffen chassis members up to 40 percent.

Higher densities of foam can increase stiffness by up to 300 percent. Since we cannot retool custom parts to redo the Z's body, we figured that this would be an excellent, low-cost way of greatly increasing chassis stiffness. Injecting foam is not a new technique for chassis stiffening. The Infiniti Q45 uses this sort of foam in some of its chassis members to increase stiffness, as do a few other premium cars. In fact, the foam we chose is the foam recommended to repair damaged Q45s.

To get the correct foam for our project, we contacted Art Goldman, Foamseal's automotive product manager and author of an SAE (Society of Automotive Engineers) paper on the use of structural foam for the stiffening of automotive unibody structures. We used Foamseal's two-component foam kit, p/n 11-22 to fill the main members of the chassis. Like we mentioned earlier, Foamseal is the supplier that I-CAR, a national certification group for quality auto repair, recommends for the repair of damaged, foam-filled chassis. The Foamseal kit uses a two-part catalyzed polyurethane foam, which quickly cures into rigid, waterproof, closed-cell foam. To prep the car, we carefully masked off all painted areas anywhere where the foam could drip. As this sort of foam is a thermosetting catalyzed plastic, we realized it could be icky if it spilled on paint or any part of the car's interior. This foam is nasty stuff. It is impervious to all known solvents and cleaners.

Rubber gloves must be worn. Get some of it on your hands and it will stay there for more than 3 weeks--don't ask how we know. Do not get this stuff on your paint. Wear old clothes; we ruined ours while learning how to handle the product. We injected the foam into the rocker panels and frame rails of Project Z through existing bolt and drain holes. When injected, the foam reacts like shaving cream and quickly expands to fill the empty space. You can judge how much foam to add by watching its expansion progress through some of the holes. Once injected, the foam expands and begins to cure in about a minute so you need to work fast and plan how you inject the foam before you start.

The life of the foam kit is limited to a few hours once the seal is broken. We filled all of the Z's unibody frame members using five foam kits. When foaming a chassis, you must remember the wires and other lines that pass through the chassis must be relocated or they will be entombed forever.

We were amazed at how this simple procedure improved the performance of the car. The chassis now almost feels like it has a roll cage. A sloped driveway can be driven up sideways with nary a creak. Even though the Z already has a pretty tight chassis, it feels more solid. The ride has improved and road noise has been reduced noticeably. We bet that the car will be even more responsive to chassis tuning measures in the future. If you are a slalom racer, a road racer, have a lowered car or even just want a smoother ride; foaming is a worthy, easy-to-do modification. Foamseal has foams in densities as high as 10 lbs per square foot if you desire to make things even stiffer.

Do not--I repeat--do not attempt to use cheap, hardware-store canned foam. This is not the same thing, and if injected into your chassis, will form a gummy mass that won't dry. Foamseal foam is a professional grade foam, which although it is a little unforgiving to cleanup mistakes, has superior mechanical properties and catalytic curing so it will dry even in an enclosed space.

These changes are continually improving and refining Project Z as we eagerly await our motor. We still have some more parts that we will install and review in upcoming issues. Stay tuned, the best is yet to come


From Sport Compact Car
http://www.sportcompactcarweb.com/projectcars/0006scc_proj300zx/

[zero.counter]

Nice write up Irena! The kid who owned my S14 prior to me used that canned foam for sound deadener and it screwed up the trunk and he injected it behind the bumper (rear) as well. It did not mush like that particular article stated, but the job looked really bad.

[Maeda]

Ah in the time it took for 5 replys I found the info I was looking for...

From what I've found from the miata guys and FA is that it works extremely well for stiffning the chassis when used in the sills, B & C pillars and frame rails... Infinity uses this stuff for sound deadning and stiffness as well.

It belongs in the frame of the car not the bumper... and it's not the stuff you get at homedepot in the can. Urethanes come in different densities(the foam we have at school is stronger then a good piece of wood no joke) and the automotive one is much denser then the junk for filling cracks in your floor.

So i'm buying some and filling my frame with it. ^_^

[95Blue240sx]

this stuff sounds pretty cool, but i dont know if id want to use it. sounds messy. maybe i will though. how much does this stuff go for?