Anyone foam fill their chassis?

I've been considering stitch welding and foam filling the chassis in the commute attack car. Anyone have personal experience or valuable insight?

This is an article from sport compact car from a dog's age ago……

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.

The Foamseal Two Component Foam Kit consists of two easy-to-use aerosol containers of material with a nozzle and a mixing chamber.

As the foam cures, it expands with the excess coming out of the holes where it was injected. Note how it is important to mask carefully. If you accidentally use too much foam, you could have much more coming out of the holes than we did. If it gets in the carpet, it will never come out.

I've never heard of it before but that is interesting.

Yes, it works to a degree. You will find a few thousand links on the internet to people using cans of "great stuff" expanding insulation foam, people gluing foam board to the chassis, and other complete BS junk.

I can't find the link, but there are some foam products that do work. They will come in liquid, two-part form and are actual structural foam. When used properly, they can stiffen a chassis. The results seem to be mixed depending on the chassis for obvious surface area reasons.

I had seen one where someone filled a Sentra chassis with foam and had some impressive results but I can't even find it on googles now.

We did something like this on an oval kart chassis but we used rubber bushings at the end of the frame instead of foam.

I'd see about underbody bracing instead. What car is it? If there was a convertible version, pre-engineered bits might be available. G6 convertibles have massive amounts of underbody trussing that will go under a G6/Malibu, for instance.

I say this because foam filling needs to be done with the proper products and reactions are mixed, seem to be centered around noise abatement mostly. Which is not to be discounted, a lot of NVH is Noise masquerading as Harshness or Vibration. Drive with earplugs in and notice how your car seems to ride better! (Brains are funny things, they over-interpret inputs)

And stitch welding is not really a weekend job, either. The biggest problem is getting the seam sealer out, which tends to be a bare shell and rotisserie job. Then the seams rust out quickly because you can't really repaint the inside of box sections.

I did it on our challenge car a decade ago.

The article from SCC had some sources of the two piece foam- but they don't do it anymore- at least specifically for cars. So you need to find a good closed cell two piece set up to work.

I spoke with some older Alfa racers who did this exact same thing a long time ago- they loved it in their car.

There IS structural foam available. Just not sure where to get it anymore. I'll have to check the very expired cans that I have for ingredient.

We ended up having to take it out, as we had to do some welding. Still, I'd do it again.

Any water that makes it's way between the foam and the metal greatly accelerates rust. In my case I had thought it would work to keep water out and slow decomposition. I was exactly wrong.

mazdeuce wrote: Any water that makes it's way between the foam and the metal greatly accelerates rust. In my case I had thought it would work to keep water out and slow decomposition. I was exactly wrong.

Came to say this. Undoubtedly good from a performance standpoint, but it causes the frame to rust out pretty quick. It would be good for a car that you're going to race and then scrap.

In reply to GameboyRMH:

I'll add, as a guy who's welded up hundreds of rusty cars, foam in the rocker panels etc is a huge pain. We don't want to breathe it when we weld and we don't want to burn a car and our shop to the ground. Customers get to pay quite a bit extra to have us deal with it. I'll also say we've seen quite a few seam welded race cars where the welding was bad and did more damage than good--like knock the whole car out of true. Not to be a downer, but be careful.

--Carl

www.eclecticmotorworks.com

Alfa did use foam to strengthen the chassis in the 70s in some Alfasuds. IIRC it was in the rockers, but I may be mistaken.

It ended up making them rust even faster, which is quite an achievement.

Can you get mixable foam (expanding or similar) that is closed cell? The great stuff and its kind are open cell and just soak up the moisture.

In reply to singleslammer:

You can get a hydrophobic, or closed cell foam. However that still doesn't prevent it from being a rust factory.

It's been several years but we bought various polyurethane products from a company called Emicole or Emecole. Something like that anyway.

Knurled wrote: I'd see about underbody bracing instead. What car is it? If there was a convertible version, pre-engineered bits might be available. G6 convertibles have massive amounts of underbody trussing that will go under a G6/Malibu, for instance. I say this because foam filling needs to be done with the proper products and reactions are mixed, seem to be centered around noise abatement mostly. Which is not to be discounted, a lot of NVH is Noise masquerading as Harshness or Vibration. Drive with earplugs in and notice how your car seems to ride better! (Brains are funny things, they over-interpret inputs) And stitch welding is not really a weekend job, either. The biggest problem is getting the seam sealer out, which tends to be a bare shell and rotisserie job. Then the seams rust out quickly because you can't really repaint the inside of box sections.

This ↑

Underbody bracing will achieve almost the same thing (except for sound absorption), will be faster, likely cheaper, easier to source, and reversable. I plan on working something up for my DD as soon as Im in my new garage and get my welder after the new year. Have 220, will fabricate.

I can't speak to any of the structural foams, but I know Great Stuff can be surprisingly heavy in large enough quantities. It's much denser than, say, styrofoam.

Just google "2-part urethane foam and you will find plenty of places to buy it.

http://www.uscomposites.com/foam.html

I've heard of using it in boats, but it never occurred to me to use it in a car.

I did it in my rockers a few years ago. Ruined the car. Rusted out overnight.

The back side of metal surfaces, and inside chassis tubing and components is not painted. Humidity in the air will find surfaces to condensate on, even if they are "contained". The foam (even closed cell) creates a temperature differential which makes the back side of the metal an attractive place to condensate. Then, with no air flow, it never evaporates, and parts rust from the backside out.

Open cell is worse, because it acts like a wet sponge. But both are not good.

It was a big (and VERY costly) mistake.

Most components in boats are not metal. Wood, or fiberglass.

It works fine there because of no condensation.

Thanks for all the replies. The car is a 2000 mr2 spyder that has a roll bar as well as all commercially available structural bracing, doesn't see winter and lives indoors. I would be doing the stitch welding and foam filling myself using my mig and lift. It is a gutted race car. I was not considering using great stuff or any other non-automotive foams. I had heard that the closed cell foams that are designed for automotive applications actually prevent oxygen from reading the metal and prevent oxidation. As far as weight added by doing this the foams I'm considering are 2 and 8 lb per cubic ft.

SVreX, what type of foam did you use?

BMW also uses a 2 part foam to prevent subframe tearing on e46s. You fill up the area in the trunk between the outer and inner floor pieces. That kit is probably still available for purchase.

I found this, kind of interesting……kind of lacking in the closure department……..

http://www.sr20-forum.com/brakes-suspension/11917-foam-filling-chassis.html