Wanted to throw this into the Suspension forum because this mod would better relate to this section more than the body section.

Anyway DelSol, Miata guys and even a 300Z have had great success with filling their sub-frame channels, rockers and few other chassis voids with expandable foam. We also discussed this a few years back in the Supra community but since I installed a 6 point cage it was pretty useless to go through with this mod.

The idea and theory behind this is that it not only adds rigidity to your chassis (depending on foam density) but coupled with a good suspension set-up it'll allow that suspension to work more efficiently. It does this by eliminating a lot of the so called "shock" the chassis sees when running stiffer springs/shocks. This in turn can help improve upon your suspension adjustments and the car becomes more predictable.

Here's a link to the expandable ridgid foam that I think I'll use. FOAM It's closed cell so I won't need to worry about it absorbing water. Plus, most of the jig pin holes in the frame will need to be covered up anyway so the foam does not leak out. Haven't decided on the density yet but I definitely would not go anywhere below 4lbs. I also haven't really dug into the car to see exactly where some of the other spots would benefit from the injection. Guess I'll get started on that soon before I order.

Anyway, just looking for some feedback and opinions on what other portions of the Z chassis might benefit from this..

 

new ford pickup trucks have this to reduce noise. im tryna figure out how it would help rigidity. sure its more dense..but metal is FAR stronger than foam. you could probably benifit more by triangulating the hell out of the frame

 

Let's see, the best way to describe this...


This is a very subtle explanation, but get a piece of PVC pipe and see how much it'll flex and twist. Now inject that same piece of PVC pipe with a high density rigid foam and see how much of that flex and twist is eliminated. The higher the density of the foam used the more rigid it becomes. Almost to the point where it will hardly flex.

Same principle here only on a higher scale. The metal frame still retains the job of adding rigidity to the car but being that it is hollow, does a poor job at equally distributing various loads. By injecting a high density foam you cure that problem. The key is choosing the correct density. The more the better but if your concerned about weight you'll have to play with the numbers.

Also, ensuring that you inject the right sub-frame members will play a big roll in the success or failure of this kinda mod. What's the use of injecting both frame rails yet leaving the cross braces untouched? That's one of my goals is trying to locate the best places to inject.

BTW, the lower density foams are more for chassis noise control than rigidity. They're more along the lines of 2lbs per cubic ft. Once you start jumping up to the 8-10lb. densities in the frame rails, you're getting into the "chassis stiffening" arena.

Does this better explain the concept?

 

Interesting..Subscribing.

 

what all do you have planned to the car? That is a very big step to take, and a totally unncessary one (IMHO) for a street car

 

i thought people try to remove foam/sound deadening material for weight saving purposes...

if you fill the chassis with expandable foam (polyurethane mixture of various densities) that stuff gets heavy REALLY REALLY fast. AND when it cures, it actually contracts a little bit... (not to mention it gets EVERYWHERE and it stinks)

imho if you want a stiffer chassis, getting something like the GT brace or a weld-in roll bar would probably be better, and the roll bar can double as a harness bar for the track-

 

I would think that adding that much weight would negate the benefits derived from the extra stiffness.

IE:
The weight added to stiffness added ratio would make this mod detrimental instead of helpful.

 

To Stop Rattles it might be worth a look.. The Chasis does need some flex you know..

 

I think it'll add over 100lbs of extra weight, depending on how much you plan to add.

 

Take a metal pipe and repeat the same procedure although you might need a machine to flex the pipe. See if that does anything. In theory it might work, but I cant see it adding that much rigidity. Better than actually doing it might be to have someone model it in a program to see what happens. There has to be someone on this forum with access to a program like that. Would Pro-E be able to duplicate that test?

 

1. it absolutely works...there are plenty of cars out there that have done it. I know JUN Japan uses this on one of their Time Attack Evo's and offers it as a service to their customers

But the question is....for a car that sees only a once in a while track day (ie is not a race car), why bother?

 

This will not stop rattles, be real here.

 

It’s an interesting idea and would probably work.

Will you be stripping the car’s interior? The sub frame might be void, but the rest of the chassis probably has a bunch of separators (the noise reduction expanding foam brackets) that will prevent the foam from going every where. That would be a minor problem.

I’m more concerned with the side impact air bags, if your car is so equipped. The impact sensors might be affected by the foam, changing the airbag deployment timing in case of an accident. Not something you want to tamper with.

 

theres someone with a scion tc that did this. his sn is ramaudio on scionlife.com if anyone feels so inclined to ask him how his car changed after doing this

 

Nissan does this from the factory with the Q45. Aswell as many high-end manufactures. If your going to do this, you'll have to relocate any hard lines in the affected areas. You might want to look into seam welding the chassis. Bigger commitment, but FAR mor effective.

 

I filled the rear strut bar with foam last year to knock out some of the resonance. If you tap on it with a screwdriver now it is a dead thud.

As for the rest of the car it's tough to call. I am worried that if I ever need body work in the future, this stuff would be a mess to clean out.

Chris