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95 Impreza L
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56 Posts
Discussion Starter #1
So I have read a few of the big chassis stiffening threads and I seen several people interested in the polyurethane foam for chassis stiffening. I also understand that there could be rust issues.

I was wondering if anyone has actually done the polyurethane foam on their chassis? I am looking for some advice on it, as I am considering this to do over the summer.
 

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99WhiteMock22B/10TeslaRoadster
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I'm just curious about this as it doesn't seem like the best idea but I haven't the slightest clue so just here for some more knowledge.
 

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MY00 //// BRP 2.5RS coupe
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a buddy of mine has used it in their lemons race car.

It works, but you just need to carefully cover up whatever holes you don't want the foam to go in.

I say it is okay for a race car, but in a daily car, the passages that will be used to inject tend to be for water drainage and the foam might trap some of the water and eventually cause rust.

There is no way to completely fill all voids as well, therefore most teams are content with just a really nice cage! (adds safety as well)
And if you go about drilling holes to fill voids strategically, better off with a proper cage.

From modified magazine
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.

Here is a to the foam:
http://www.foamseal.com/auto_aftermarket.htm
 

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95 Impreza L
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56 Posts
Discussion Starter #5
Thank you this is what I was looking for. Now what I am wondering is besides the frame rails where else should I foam? (of course this is assuming that i decide to do it, dont wanna rust out my car)
 

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MY00 //// BRP 2.5RS coupe
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I really suggest proper cage if such strength is needed, because foam is not reversable and will be added weight. If you decide to get a cage later on.

Not much more places than the usual parts of the frame
 

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99 2.5rs Coupe
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a buddy of mine has used it in their lemons race car.

It works, but you just need to carefully cover up whatever holes you don't want the foam to go in.

I say it is okay for a race car, but in a daily car, the passages that will be used to inject tend to be for water drainage and the foam might trap some of the water and eventually cause rust.

There is no way to completely fill all voids as well, therefore most teams are content with just a really nice cage! (adds safety as well)
And if you go about drilling holes to fill voids strategically, better off with a proper cage.

From modified magazine
You could try using a heat gun on a dry day to get all moisture out and then foam it. If everything is full of foam there shouldnt really be any way for water to get in at all. Phase garage did a build of it and the car was really well done and still usable as a daily.
 

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Experimenter
Tubaru Pickup
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Is this why I couldn't find any great stuff on the shelf at homedepot when I had a draft to fix in my basement
 

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Baby❤Daddy
98L Wagon
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SCC magazine did this in the project z32 with good results. i'm too lazy to go dig out my copy of it and take pics. also, i don't feel like googling.
 
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