Hi there,

So over the years I have seen all sorts of ideas, lots of products etc..

Seems like we are chasing our tails.

Here is my dilema, and I would like to get some input.

Take a 34 year old chassis, fix the rust.
Add super stiff suspension.
Bearings, bars etc.
add really sticky rubber.

Now, what gives in the chassis...where is the weak spot.
Say I seam weld the suspension console.
What next...something needs to flex, or it seems to me that something will break instead.
I ahve seen pics from McMark of a cracked long inside, and in the miidle of the span..not a rust issue per se, but a fatigue issue.

So, where can I engineer in flex, so the chassis wont crack, or break a weld.

No Cage allowed.
Just the chassis.
Currently there is not inner long kit, or outer...just good repair work on the rust to date...
Nothing is cracked yet...but something will have to give..
I just put in roller bearings....now its really smooth, but now more of the forces are put directly into the chassis...

Rich

there's your real problem ...


the weakest point is the longs right about where the upper windshield hoop is located.
if you plan on running super sticky tires, the only way to go would be a full cage.
the long stiffening kit will help a bit, but not much.

the only other thing i can think of would be a solid roof or at least a solid X-brace under the roof.

short of that, you are out of luck. there's just not enough rigidy in that area without a full cage ...
Andy

Weld the dorrs shut to add some more strength?

You are trying to use a 4"x6" sheetmetal tube to keep the while car straight. It just cant keep up w/ modern tires w/o some help.

BJH

I think maybe I did not ask the right way.

How can I engineer in flex.
I know it will, and I would like to let it flex, just concentrate that flex to a certain area..

All new tires are more sticky, and not everyone has or wants a cage..
I know the minute I put a cage in, I might as well never drive it on the road again, cause for me, that is the first step into the abyss...the racing abyss.
Till then, why not think of it the other way.

Let it flex, but let it flex a certain way, and in a certain area..
If I put in the engman long kit, and the outer rocker stiffeners, then where does it go...it will flex somewhere..but where?
It is better to let the long flex?
Or move that stress to the fender welds (those would be next)

Im just thinking a little bit outside the box, cause its raining, and I cant drive it...

I think you're looking at it wrong. Yes, the flex does 'move around', but each improvement reduces flex. So you're not talking about concentrating flex, so building in 'flex points' would only negate your modifications designed to reduce flex. I think your idea has some merit, but I think that without realistic FEA, you're shooting in the dark while drunk.

Shooting in the dark works sometimes...

I guess my worry is, where is it going.
I know its gotta go somewhere.
So what is next.
I fix the suspension console, done
Inner and outer long, done

Now, where do I watch...
I am guessing that the front fender welds to the front firewall, and the inner and outer fenders are next...something needs to take the force,,,

I would love a detailed FEA, but who has that kind of money and time..

I was thinking more of a rear suspension console that allows for this type of movement. Something predictable.
Something that allows the suspension to absorb the stress, instead of pushing that force into the frame/unibody.

So , instead of a detailed analysis of the frame/body....more of a look at allowing the suspension to absorb more of the twisting force that is applied on a skid pad, in high load , high g-force scenarios.

It seems to me that we have improved lots of the car already.
Look at the issue, or smack me.
If the trailing arm is super rigid, and allows zero twist at all, then its all up to the tires..
We have trailing arms that twist from the factory.
Take out the twist, and the force starts to add more stress to the trailing arm mounting points.
So we have a fix...solid outers, and re-enforced inners.
Ok, now where does it go...up into the long, and applies the side load force to the lovely weld at the shock towers...woohoo..that is a hard one to fix, and fix well enough to keep it from breaking..but it can be done..

If you follow my trend here.
Instead of rebuilding the car entirely,,all new welds, and all new heavier parts, why not figure out a way to control the twist at the trailing arm.
Not only control it, but limit it.
It can twist, but only so far, so you dont make the rear tire patch worse in a turn, but also you let it twist from say 2 degrees to -2 degrees...

This came to me as I watched the speed channel prototypes racing today.
Those wheels move alot...from 3 degrees or more up to almost 0 degrees.
It just looks like it is designed to do that right from the start.

Its just a thought..

Rich

Rich

Where do you engineer the flex to occur ??? Everywhere.

The ideal would be minute amounts of flex equally distrubuted along the entire chassis.

In a perfect "world" it would only flex at the tires and springs. But, this is a "914 World".

DSM has it right. As the chassis gets stiffer, the suspension takes the flex. That is why you want a stiff chassis. There is no designing in flex areas.

If you look at many newer cars that have been engineered for ease of assembly with parts/systems/assemblies sourced from all over the world you see sub frames that bolt to the chassis with 4 - 6 big bolts...from these sub frames, all the suspension is hung.....and maybe a shock mount on the unibody...

Are you looking for this type of solution? Say you cut off the rear suspension console and fabricated a sub frame to accept the trailing arms...this may isolate the forces being transferred and possibly reduce the stress on the unibody, but there is alot of engineering, testing and fabrication here...ultimately I believe you would be adding substantial weight and changing the chassis dynamics....basically building your own car using a 914 for a starting point.

I'm with ya...no roll cage here either...I'd love an easy solution, but I think you have to work with what you've got...I don't want a miata!

Put in a cage, stiffen up the chassis. Let the suspension take all/most of the flex (it's made to move around).

Crap thats symple! No role cage is no big deal. All is required is thingking out side the box or should I say inside the box.


One can stiffen the car and still have it completely STOCK looking. I've been thinking of this for a while and have come to the conclusion that if the boxed frame longs were used more as a hiding place for a DOM subframe which would tie into all the so called week links of the unibody, it would be the tits. The longs can be cut open underneath, gutted, beafed up and recaped; welded back to their original spot.. You also need to remember that all vehicles are designed to flex which is very evident on body over frame designs as well as many unibodies. It all depends on what you want to accomplished which kinda sounds like something which the car was never originally designed for; much like the rest of us who beaf up the suspension and add role cages.

Admit your sick like the rest of us and do what you want. My sugestion is if its a beater then go wild, if its restorable please, don't bastardise it:beer1:

My degree is in toxicology, not engineering, but along the lines of what other said...
Raise your suspension pick-up points, give the suspension more travel, and that is where you can reduce stress/flex in the chassis.

The inner/outer long kits are proven - do them and maybe add more. No roll cage, but what about X-braces in both trunks to reduce twist, maybe brace from top of rear shock to upper+lower firewall to bridge the engine bay gap???

My 914 has flex points, they are a reddish brown color and flake when you scrape them