Structural Rigidity enhancement...

[jcsaleen]

The reason why is because I fear the car has been damaged/weakend due to an accident six months ago which swayed the nose. the Rx7 is a very "flimsey" car persay. It has one of the best suspensions (Double wishbone) but the frame is very flexible an flexes very easily. I don't have very many tools at my disposal so when I need to do routine stuff I do it the "ghetto" way persay. I did an oil change once by pulling half the car up on a high curb an draining the oil out like that. When I opened the doors and an trunk to get somestuff an it was on an angle I couldn't close the trunk nor the hood or even the drivers side door! That is very serious flex to me.

[drunken monkey]

ok.... so in short, you have wrecked your car then.
if there is that much flex to begin with, injecting expanding foam into the frame might not be the best thing to do and won;t actually do any good if the frame is already compromised. By the way, if simply putting the car on a curb causes body flex, then I'd say that something is/was wrong with your car. The RX-7 shouldn't be like that. From what I recall, the car is meant to be very stiff structurally but on softer springs/dampers; very much like the MX-5 and RX-8 and that is what makes it so progressive.

[KiwiBacon]

Originally Posted by jcsaleen

Strength yes, Saftey No.

Sometimes hollow is better and it's a foam that harderns into a solid plastic not a foam that turns into sponge or cushion. Do you know that your bone structure is almost the same structural patterns as this foam? Many things through the years have been many or hollow peiced an the fact is they're stonger. Perfect example is carbon fibre... Why is it so durable and strong because it's a fiber an not a solid monopiece structure.

Honestly I don't care about safety because a cage in an FD really won't do that much as far as safety at the speeds I access in the FD are no where near safe even for a cage.

You are not going to get any strength or rigidity at all out of urethane foam. Have you ever played with solid urethane? It is very flexible, hence the use in suspension bushes. It is so flexible that bicycles use solid blocks and rods of it for suspension springs.

If you don't believe me, then I suggest you do some experiments with the foam first. Fill up something like a balloon with it, let it harden and see how stiff/strong it is.
It'll be about 3 times stronger than a dry kitchen sponge..

Human bone does not compare to steel for strength. Neither does urethane foam.

Carbon fibre is not related to this discussion at all. But carbon fibres are exceptionally stiff, stiffer than steel.

[jcsaleen]

Originally Posted by drunken monkey

if there is that much flex to begin with, injecting expanding foam into the frame might not be the best thing to do and won;t actually do any good if the frame is already compromised.

It's already been scanned and it's fine...

Originally Posted by drunken monkey

By the way, if simply putting the car on a curb causes body flex, then I'd say that something is/was wrong with your car. The RX-7 shouldn't be like that.

It is an I know there's nothing wrong with this Rx-7, 44k original miles an not one incedent up until 5 months or so ago.

Originally Posted by drunken monkey

From what I recall, the car is meant to be very stiff structurally but on softer springs/dampers; very much like the MX-5 and RX-8 and that is what makes it so progressive.

Depends on the package you get (the only difference is springs an a strut bar) FD's are very flexible cars maybe your confusing it with the FC3S. The Fc3s was a tank because of how structurally sound it was.

[jcsaleen]

Originally Posted by KiwiBacon

You are not going to get any strength or rigidity at all out of urethane foam. Have you ever played with solid urethane? It is very flexible, hence the use in suspension bushes. It is so flexible that bicycles use solid blocks and rods of it for suspension springs.

Originally Posted by KiwiBacon

If you don't believe me, then I suggest you do some experiments with the foam first. Fill up something like a balloon with it, let it harden and see how stiff/strong it is.
It'll be about 3 times stronger than a dry kitchen sponge..

I will, But having seen a 700 4-whp BNR32 GT-R be injected with it for structural purposes I think it sets a good example. I'll trust the pro's at Apex'i tuning.

(Apex'i Kyoto Hakubai BNR32 GT-R)

[curtis73]

All cars flex, its just a matter of how much.

The foam has been shown in many applications to do wonders. Driveshafts that were installed behind Duramax diesels hold up to well over 1000 lb-ft in part because the thin-wall aluminum shaft is injected with urethane foam.

Have you guys ever used a can of that expanding foam? You know what its like after it hardens? Well the urethane foam is like that times ten. It is VERY effective at helping. How much depends on several factors, but I don't doubt that its an effective means of helping rigidity.

I know it seems illogical given its light weight, but seriously, its like adding epoxy to fiberglass. Neither one is very strong alone, but put them together and they are very strong. The foam gets its strength from the billions of geometric shapes formed in the bubbles.

[GreyGoose006]

then it seems to me that the reason for the stiffness isnt the foam at all, but the fact that it expands.
it is no mystery that when you put an object under tension it is stronger.
this science was recently used in golf clubs and yeilded huge gains in drive length.
not to say that golf clubs compare to a frame of an rx-7, but the general idea is the same.
preload the frame with a certian ammount of tension and it will be stronger.
how much stronger, i cannot say, but it could help some.


personally, i'd check that frame again.
if it contorts by simply putting it at an angle by driving it onto a curb, then you are starting way behind.
how hard would it be to find a doner car with the stiffer frame and swap in all your parts?
it would certainly be more cost effective than trying to stiffen a frame that is weak to begin with.

kind of like turboing your grandmothers buick.
it will help. thats obvious. its just a bad platform for a build.

thats just my opinion

[jcsaleen]

Originally Posted by GreyGoose006

then it seems to me that the reason for the stiffness isnt the foam at all, but the fact that it expands.
it is no mystery that when you put an object under tension it is stronger.
this science was recently used in golf clubs and yeilded huge gains in drive length.
not to say that golf clubs compare to a frame of an rx-7, but the general idea is the same.
preload the frame with a certian ammount of tension and it will be stronger.
how much stronger, i cannot say, but it could help some.

Yes, I see what your saying... almost a roman arch effect like a keystone.

Originally Posted by GreyGoose006

personally, i'd check that frame again.
if it contorts by simply putting it at an angle by driving it onto a curb, then you are starting way behind.
how hard would it be to find a doner car with the stiffer frame and swap in all your parts?
it would certainly be more cost effective than trying to stiffen a frame that is weak to begin with.

kind of like turboing your grandmothers buick.
it will help. thats obvious. its just a bad platform for a build.

thats just my opinion

It's more of a promise to keep persay. I already had the frame checked an it's fine it just needs a new headlight assembly/structure. The way the car hit wasn't direct but on a spin an angle so it wasn't a direct hit to the frame just a tweak. Besides my chassis has to low of miles to give it for minor damage...

She's a real gem if you see her in real life

[KiwiBacon]

Originally Posted by jcsaleen

Yes, I see what your saying... almost a roman arch effect like a keystone.

It's actually the opposite. Roman arches work because they're in compression. Goose was talking about the structure being in tension due to internal pressure. Just like a tyre with the pressurised air inside.

Just because you see something done on a video, doesn't mean it's safe or even works.

I'd hate to see someone hurt or even killed because they think some plastic foam can make their car stronger than a roll cage will.

[jcsaleen]

Originally Posted by KiwiBacon

It's actually the opposite. Roman arches work because they're in compression. Goose was talking about the structure being in tension due to internal pressure. Just like a tyre with the pressurised air inside.

There's no pressured gas or air it just turns into a solid substance.

Originally Posted by KiwiBacon

Just because you see something done on a video, doesn't mean it's safe or even works.

Like I said they showed runs with it an all. Launched an performed great. If it was some backwater shop I would'nt even think of it but Apex'i does wonders especially to their GT-R's and Fd's.

Originally Posted by KiwiBacon

I'd hate to see someone hurt or even killed because they think some plastic foam can make their car stronger than a roll cage will.

A plastic foam won't make a difference in a crash. Like I said before I'm not going for saftey only rigidity enhancement and a stiffer ride.

There's always people who doubt that thing's "cannot be done" or "won't work" but ever since the invention of the 3 and now 4 rotor I come to think any thing is worth a shot.

[curtis73]

You guys are missing the point of the foam. Its not pressure, ITS THE FOAM ITSELF. Try it sometime with just the cheap can of spray foam in a piece of exhaust tubing, then span it across a couple boards and stand on it. Compare it to a non-foamed tube and you'll see.

Think of it this way. Lets say you got inside the tube and welded in about 10 braces across the tube at random angles. It would strengthen it, right? Now, think about doing that with hundreds of billions of hard hair-strands of polymer. Its the same thing. You're taking a bubble of polymer (not very strong) and multiplying it billions of times in geometric shapes. Its strong stuff.

[GreyGoose006]

is it similar to "great stuff"
i've got a can or two of that laying around...

[drunken monkey]

i'm aware that foaming the chassis works.
my point is, I'm not entirely sure if parking your car on a curb should be causing that much longitudinal flex in the chassis to a point where the doors or boot can't shut.
If there is a weakness there, filling it with foam might give you temperary strength but the frame is still gong to be compromised.

What kind of scan did your car have?

when he said that there is strength gained from internal pressure, he is talking about the pressure caused by the foam wanting to expand and the frame not letting it. This is also what I was talking about when I said it would put extra stress on the joints of the frame.

Why do you want a stiffer ride?

[GreyGoose006]

my biggest argument is that if the foam cracks, you will be left with an unevenly stiff chassis.
you compared it to bone, and bone cracks pretty easily.

i guess i have to try the "great stuff" experiment.

[2.2 Straight six]

i doubt an aerosol of this foam will deliver the kind of rigidity you expect, if there is such a gain to be had, as shown by this GT-R i'd imagine they used some gear a little more "heavy-duty" than squirting a can of foam into the frame's hollows.