Rear Suspension Reinforcement Options

[J P Stein]

The conventional wisdom for stiffening either (or both )
ends of the car is to start with a roll cage.
Once this box section is installed (no small chore), it is relativly easy to run tube sections to the suspension mounts. Also, these sections should be as straight as possible due to their loadings being in compression and tension. Curved runs will tend to bend more or straighten, depending on load.

None of this is really necessary unless one plans to compete with the car. One also has to look at the rule book to see what effect doing the stiffening has on your class structure.

This prolly should be another thread.

[Brad Roberts]

This will help out (a lot). You have the right idea.

Now.. here is the problem:

The weekest point of the whole car is straight down from the top of the windshield. Basically drop a plumb from the windshield hoop to the frame rails. This is where the cars start to crack with big HP and AutoX. I dont talk about it much, because most of my guy's run cages, but this is where the BradMayeur kit works very well. I actually (in the past) have welded what would be a chassis stiff kit plate along the inside of the frame rails. I can hide this with carpet.

The piece starts around the bottom of the speaker area and runs all the way around the firewall to the to the other speaker area. Lots of welding... but MAN does it stiffen the car. I think this combined with your thinking on the rear support would work great.

B

[r_towle]

Brad,
It seems to me that a weaker link in the car is where some dumb ass drilled a 2.5 inch hole into the "frame" right below the firewall for the heat pipe.
This still amazes me that they would do it right where that section turns to horizontal and put the stress on the outer rocker. (this is a simple reason that the apprenticeship engineers should never be let near a car until they have raced)

In the days this car was built, outer rockers where almost sacrificial parts that we all knew would rust.
To put that much stress on that part of the "frame" is insane IMHO.

This is where the car bends when jacking (both my complete cars) and this is what I am trying to fix with less than a cage...

I was thinking that a piece of 1/8 or 1/4 in steel, basically a triangle in front of the firewall maybe 12" by 12" would help, then tie that in with the inner longitudinal fix that you propose (BTW I love that idea, easy to do, less work than the meyers kit IMHO)

Then connect the rear suspension to the firewall, right behind the top or the plate...steel going through the hole/cup to the suspension might work...

Also considered running a pipe like a harness bar, but inside the engine compartment to tie the two bars running to the suspension together...little 45 degree 3 by 3 corners welded in...

Basically I am trying to NOT put in a full cage...
But rather a lower cage front to back...

I would propose to tie in the front to the sections near the speaker...although outside the front "firewall"

Thoughts and advice needed and gratefully absorbed...
This will run in both a 2.0 liter AutoX car as well as a special project 914/928 that I am going to do, although the 914/928 one will be a true convertible...
This one I may ship over to you and have you do all the metal/custom lower cage work to ensure good welding..

Rich

[Brad Roberts]

Rich,

what I have found: The outside frame rail is thicker than the inside. I do agree 100% that the heater duct opening at the base of the firewall needs to be addressed. Once I found out the inside sheet metal of the frame rail appeared to be thinner.. we came up with the idea to stregthen it. Brad's kit was truelly designed for rust prevention. The BITCH of his system is the jack post and what has to be done to make it work.

Last night a 914 racer and I went over a accident in his race car where he was hit in the side at more than 100mph.. the firewall collasped over 4 inches behind his seat. He now runs a a 2inch by 1 inch thick steel "bar" from one side of the engine bay to the other side of the engine bay. This sits right below the engine lid and cannot be detected when the lid is in place. It mounts just below the hinges for the engine lid. He commented on how much stiffer the new car was with that cross bar welded in.

B

[Gint]

This thread is Grade "A" prime. Don't stop now. Toss it out there.

(IMG:style_emoticons/default/pray.gif)

BTW - How 'bout "Brasshole"

[Jeroen]

Hey Rich,

No offense, and all IM(very)HO, but I think this way, you're aiming all the stress to one point (the point where the frontbars meet the framerails in the passenger compartment).

Basically, as with any cabriolet, that would be the weekest point of the car.

I think the only way to get the flex out of it is to compensate for the absence of the roofstructure (by ways of a full rollcage).

You can try to reinforce the rockers all you want, but it would still be the only area that got all the stressloads.

Any reason why you don't want a full cage?

Cheers,

Jeroen
(not dissing your ideas, just brainstorming along)

PS here are my "cage plans" for other to shoot at

[r_towle]

Sorry for not re-visiting this one, life got in the way.

I am still trying to get a grip on several issues here.

I understand the benefits of a full cage.

It seems to me that if you build the lower part of the chassis the right way, you could reduce (not eliminate) quite a bit of the flex.

Another thought I had was why not remove the outer rocker...(kinda have to due to rust anyways) then make a ladder bar or a solid piece of plate that welds into the inner longitudinal on the vertical plane, paint that and put on the new outer rocker...
Seems, aside from the heater hole, that would add the strength enough for autocross and aggressive street driving.

Brad, I love that thought about the bar under the engine lid, kinda what I was looking for with the bar from side to side tying the bars together.

but now I will put a triangle from the middle down to the lower firewall on both sides.
So a tube goes from the shock tower to the seatbelt mount on the rear of the firewall.
A tube will go from each of those tubes, across the engine compartment,,,and in the middle of that tube would be tubes going down at 45 degrees to the lower firewall.

Now, what size tube would you use???
I would prefer lots of lightweight triangles versus several heavier ones...
I an willing to break the triangles down to smaller ones to reduce the tube size...

Need help on this question...

Rich

[Brad Roberts]

Use legal .095 Inch and half. This is good for cars up too 2200 lbs. We have to use .125 wall on cars that weigh over 2200lbs.

B

[Tony C]

I little addition/correction to Brad's post: You have to use 1.5" X.095 DOM steel up to 2200lbs and 1.5 X.120 DOM steel up to 2500lbs. You MUST use DOM steel not HREW office chair material or the tubing sizes/thickness' change.
-Tony

[Brad Roberts]

Oh yeah.. DOM all the way. The first inspection for the new cage would go something like this: Um.. ha ha ha... oh ha ha ha.. You used... office chair tubeing..LOL

Sorry.


B

[Dave_Darling]

In a nutshell.. he said that the side we weld the kit is not the week side. The side with the exposed pivot arm is what tweaked first in side load testing. They could not get it to twist without completely breaking.

And yet, back in the 70s they found on the Ginther and Maas race cars, that the arms were flexing. Talk to Anderson about this some time. He did not say how they found that the arms were flexing (I assume they instrumented it, but that is just an assumption) but he did say that boxing the arms cured that problem.

I myself would probably not use the trailing arm reinforcements. However, there is some data to support their use. (BTW, I think that the above is where the boxing of the arms comes from, not from the factory racing effort.)

--DD

[Brad Roberts]

I have chatted with Bruce about this, what he admits in public isnt always what he admits in private.

One of Ginthers original crew guys owns a business at Sears point and frequently visits us here at SSI. I have lots and lots of "from the horses mouth" information. Good stuff. He lived 3 doors down from Ginther in SoCal and became a big time Mustang racer.

I cannot imagine that they had the tires we have today. I would have assumed that the problems (if any) would have shown up on every car that runs slicks today.

B

[Jeroen]

Hi Rich,

Here's some ideas for you
Tony and Brad will prolly skip in on if it will work or not...

You could also run the rear uprights behind the firewall, that way you'd get very little interiour intrusion

Cheers,

Jeroen

[Brad Roberts]

Looks good to me for a aggressive street car. The front tube doesnt need to go that high. It can stop at the back side of the fenderwell. The fenderwells are very very strong material. Welding to them as high as you can go in the cockpit will be just fine. You will get the same effect as if you went through the firewall.

I wish I could draw.

B

[kuch]

If you stiffen a street car, will this eliminate the body flex that causes the rear signal light lenses to crack??? (IMG:style_emoticons/default/ph34r.gif)

[Brad Roberts]

Kuch,

how much HP you pushing through a 914 ??? I have yet to crack a lense from body twist.. ha ha

This should be good.

B

[kuch]

(IMG:style_emoticons/default/blink.gif) Not enough.......I just thought that since the car was dubbed the "flexy flier" that this is the cause of all the cracked lenses...over the years I have quite the collection of cracked lenses.

[r_towle]

Jereon,
Could you send me the drawing without the red lines...
I will draw it the way I'm thinking.
just post it here and I will edit it...Just to lazy here to erase your lines...hoping for the raw drawing of the car please......

BTW, Brad....I got you understanding this is an aggresive street car, no cage inspection will be done.....

Please take a look and re-address the tubing size question. I think I can use tubing that is smaller than roll cage tubing and achieve my desire for a stiff car..I hope...

rich

[Jeroen]

here you are...

cheers,

Jeroen

[r_towle]

Jeroen,
thanx...
God I love the internet....
Open information is awsome...
Here goes