Adding torsional rigidity, How do I get the front half tight? Options

[phillstek]

Once again I prevail upon the expertise here.

I have stiffened the rear of the car substantially, as shown in pics. Tubes go from rear towers through engine bay and firewall to rollbar. Rollbar is plated to longs and strapped to upper seat belt mount. There is a lateral bar (profiled to clear fan housing) in the engine bay. Car has the plates around the control arm consoles as well.

So the back end is solid but I'm not sure how to get the front section solid.

I'm thinking a bolt-in bar triangulating as far forward from rollbar to long (one each side like on some factory gt's).

Maybe a bolt-in from front towers to rollbar (through fresh air vents, which don't work anyway).

I don't want to weld in the bars as I won't be able to road register the car if I do.

I don't want to re-inforce the longs with a weld in kit.

The car seems to move around the scuttle and I have cracked a windscreen to prove it. Clearly the car twists in this area and this is what I want to stop.

Any suggestions, links and advice would be appreciated.

Thanks,

Phil

[phillstek]

pictures

[pcar916]

Tying in the front towers to the rear towers through a cage is always good... that won't help your torsion problem much though. That'll take some triangulation side to side. You've concentrated the bulk of your torsion into the front of the car by stiffening only the rear. Before saying any of this...

!! Important !!!
Having a cage in a car is unsafe unless you have the both you and your passengers strapped in with 5 or 6-pt harnesses with seats designed to use them properly i.e holes for the belts. The cage, or even a rear hoop will crack heads in an accident. That said...

Too bad about the welding constraint but if bolt-in is your only choice then so be it. Adding the triangulated bar to the front of the long's is good but it will move the torsion concentration to that lateral plane. The advantage to it is that it will help keep the hoop from bowing forward when the rear towers push on it unsupported.

Given your constraints I'd,

- add a bolt-in front cage piece. Since it's still a street car...
- add low triangulated door bars from the existing rear hoop to your front cage
- Tie in the front towers to the cage
- Tie in the front towers to the front suspension mount points
- On the rear and underneath the car, you will want to add bars from the lower engine bulkhead to the inner swing-arm mounting ears

Ignore this part if you want to keep your trunk space...
- Tie the rear towers to the transmission mount points in the rear trunk. Then add an x-cross member between the rear towers or the added bars.

Unless you've removed the bulkhead in the front trunk, the front towers don't really need to be stiffened laterally in a street car.

Let us know what you decide and good luck!

[Joe Ricard]

The only way to do what you need it to tie the front and back together. via a cage.

With nothing in the middle the car will twist like a noodle right in the middle of the door openings.

when I did my race car I had gage tied to rear suspension upper shock towers. In front I tied a cross bar between the A-pillar cage bars. and then tied those intersections to the front shock towers. then with 1" tubes tied front shock towers to the front torsion bar pick ups. in an X fasion. and also put the front sway bar in a tube and tied that in with bars too. Car was damn stiff for a rookie boy wannabe racer.

[ME733]

Once again I prevail upon the expertise here.

I have stiffened the rear of the car substantially, as shown in pics. Tubes go from rear towers through engine bay and firewall to rollbar. Rollbar is plated to longs and strapped to upper seat belt mount. There is a lateral bar (profiled to clear fan housing) in the engine bay. Car has the plates around the control arm consoles as well.

So the back end is solid but I'm not sure how to get the front section solid.

I'm thinking a bolt-in bar triangulating as far forward from rollbar to long (one each side like on some factory gt's).

Maybe a bolt-in from front towers to rollbar (through fresh air vents, which don't work anyway).

I don't want to weld in the bars as I won't be able to road register the car if I do.

I don't want to re-inforce the longs with a weld in kit.

The car seems to move around the scuttle and I have cracked a windscreen to prove it. Clearly the car twists in this area and this is what I want to stop.

Any suggestions, links and advice would be appreciated.

Thanks,

Phil

.................I have never heard of....welding in bars....prohibits a car from being registered for street use.(anywhere)......kit cars are all welded in bars. They get registered......SO just alter your car to a classic "kit car" designation if thats necessary.........And no bolt in "bars" or assembly are going to be as strong as a welded assembly. maybe stripping the chassis and adding the 914 -6 chassis stiffing panels is the solution.

[pcar916]

[/quote]
.................I have never heard of....welding in bars....prohibits a car from being registered for street use.(anywhere)......
[/quote]

He's in Australia. Perhaps they're a little funny about that sort of thing... and it's about 4:30am tomorrow (24th) there now so we won't get a quick answer unless he's a night-owl!

[phillstek]

Thanks to all for replies.

Car has 6 point comp harness for both occupants and I have retained the original retractables as well.

What about a bar that ties the longs together at the front that goes up under the dash (like rollbar but hidden from view..welded) Then attached to upper front towers through firewall continued to front trunk suspension pick-up points?. Add a couple of door bars (bolt-in) and that should help right?

The authority that governs road registration does not allow bars foward of where my rollbar is and the vehicle requires annual inspection for road use.

Thanks,

Phil

[pcar916]

I think anything hidden is fair game. On top of that you could tack in a boxed section over any bars that are welded in and close to floor, long's, or anything else for that matter.

Are they gonna scrutinize the front trunk too?

[phillstek]

I think anything hidden is fair game. On top of that you could tack in a boxed section over any bars that are welded in and close to floor, long's, or anything else for that matter.

Are they gonna scrutinize the front trunk too?

I reckon I can get away with the hidden stuff due to ignorance of the RTA (I got away with the left to right conversion that way). It' the door bars that are the obvious issue for them. Trunk bars will be cool too (I think).

When you say "box" is that the same as "gusset"? Ie: plates welded to bar and mount plates in corners?

Thanks,

Phil

[pcar916]

You asked...
When you say "box" is that the same as "gusset"? Ie: plates welded to bar and mount plates in corners?
____________________

Not a gusset plate, but an obvious deception like riveting down a (rectangular cross-section) "cover" over the cage-bars that are close enough to a flat section of your interior to hide the actual bars.

It would look like the small transverse boxes welded under our seats, that our seat tilt-adjusters notch into. At least my '74 has 'em. Properly done it may pass as a structural member of the 914 unibody.

For example, a bar running along the longitudinal but covered with this box would look like part of the longitudinal to the untrained eye... not that I'm advising you to deceive your authorities! (IMG:style_emoticons/default/beerchug.gif)

[phillstek]

You asked...
When you say "box" is that the same as "gusset"? Ie: plates welded to bar and mount plates in corners?
____________________

Not a gusset plate, but an obvious deception like riveting down a (rectangular cross-section) "cover" over the cage-bars that are close enough to a flat section of your interior to hide the actual bars.

It would look like the small transverse boxes welded under our seats, that our seat tilt-adjusters notch into. At least my '74 has 'em. Properly done it may pass as a structural member of the 914 unibody.

For example, a bar running along the longitudinal but covered with this box would look like part of the longitudinal to the untrained eye... not that I'm advising you to deceive your authorities! (IMG:style_emoticons/default/beerchug.gif)

I like your ideas and as luck would have it ..a friend gave me the name of a guy who is apparently a bit of genius with the tube and sheetmetal. Has made frames for race Ducatis and all sorts of other work like that. Talk about timing, anyway I spoke to him today and loosely covered the issues and he's said he would be keen to do it.

I'll bump this thread as progress is made.

Thanks again for your help.

Phil

[db9146]

What about a bar that ties the longs together at the front that goes up under the dash (like rollbar but hidden from view..welded) Then attached to upper front towers through firewall continued to front trunk suspension pick-up points?.

If you are able to make this work, I'd love to see some pics of this....I have been thinking about something like this with a roll baradded behind the seats as you have and then using an inner long kit with a little additional gussetting here and there to tie it together.