does anybody know anything about injecting urethane into your chassis instead of getting a roll cage . from what i can find out, all you do is drill under your door sills on both sides and funnel a 1/2 can on each side. does anybody NO SHIT know anything about this??

 

I know a bit about this. It doesn't replace a roll cage as far as safety goes, so put that right out of your mind. A roll cage will still usually (depending on the type of cage) give better chassis stiffness because it's a spaceframe and not just local reinforcement of the chassis plane.

There are some foams that are better than others, you really need to use a two part foam, not single part. The results depend on the type of chassis you have, how well the foam fills the cavities (voids, etc), the density of foam used, and what kind of abuse the car will take.

If you go over rough roads or anything where the car will flex a lot, the foam can crack and lose some of it's effectiveness. Also, once that happens, it's possible to have broken and unattached pieces of foam rattling around in your chassis. It won't hurt the chassis, but it sure is fun to listen to.

Some cars lend themselves well to this, and some don't. Obviously this depends on how well the chassis is to begin with, and what types (shapes,etc.) of chassis cavities there are. You're basically turning a hollow steel structure into a cored composite structure, so there are a lot of variables involved in how well this works.

For filling, you can often use a lot of the existing holes in the chassis members, such as panel fastener or wire loom fastener holes. The don't need to be big, only big enough to fit the foam pack nozzle into. You'll need to work your way down the member, letting the foam expand and fill as you do sections at a time. You really have to fill each member in one cure, because successive fills won't get enough adhesion to each other to work well, and it isn't possible to get a secondary bonding adhesive in there. Make sure you mask everything off very well, because foam is pretty permanent on carpet, etc. Try to find something other than 2 pound per cubic foot foam, it's not high enough density to really work well and is very fragile because the cell structure is so open. The foam will tend to self-pack to a higher density in certain areas anyway, but starting with a higher density is better if you can. Higher density foam also expands less, and is less likely to deform the chassis in some areas from pressure build up. This shouldn't be a problem, but I've heard stories of pillars and things ballooning.

Make sure the chassis is really dry also, moisture causes all kinds of problems with urethanes curing.

Get a good quality brand of foam, and talk to manufacturers if you can. You want to go with something that doesn't take a week to cure, adheres really well to whatever it contacts, and has a little flex to it. Too flexible and it won't be effective as a chassis core, too hard and it won't have the durability you need.

I think I've just about covered everything. My opinion is that it's not the best thing to do to a street car. It's impossible to repair or remove, and once the foam cracks it can be rattly and annoying. I've helped a few people do this to their cars, and it's usually a fair improvement in chassis stiffness. Again, there are lots of variables. Don't do this on convertible or targa top cars (del Sol, etc) because the cyclic chassis flex is probably too great for the foam to handle, unless it's fairly flexible.

I've actually thought for the past few years that I should approach a few of the urethane companies and see if there is any interest in developing a foam specifically for this purpose, because there really isn't anything on the market that I know of that is made for this. There may be good products out there in the industrial world, but I haven't looked hard enough. The really good stuff has to be bought in BIG quantities and has a short shelf life usually, which is pretty standard for decent urethane products.

You're lucky I'm in a brain dump mood..

 

thanx for the info, you persuaded me to go with i dont think the pro's outway the possible con's. im prob just gonna save up and get a cage once again, thanks for the info

 

Yep, the cons are few but they're big ones. Someday when someone makes a foam specifically designed for this, I'll change my mind.

By the way, I love these discussions, thanks!

 

question, whats the purpose of the cage, is this a daily driver becasue thats another thing people do wrong is throw in a cage, stiffn the hell out of the car then get in a wreck and end up in alot worse shape then they would of the car needs some flex to it, unless its a trck car go ahead and supprt the shit out of it

 

What? Explain that, that doesn't really make any sense.

 

its a daily but im not goin with a full cage, http://www.autopowerindustries.com/Roll_Bars.htm im goin with the (street/sport roll bar)

 

I have heard of a lot of people filling cavities with foam for sound deadening purposes.

 

A lot of cars come from the factory with foam filled pillars for NVH reasons. .

 

Sounds to me like he's referring to crumple zones?