opinions wanted -- weld it in ? or bolt it in?

[tmctguer]

i just purchased an AutoPower roll bar for my '73 911 E. it is designed to be bolted to 4 points in the car. to do this in my car, i would need to drill 4 holes for each of the 4 mounting points. i am a little gunshy about drilling any more holes (i just put 3 in for my harnesses).

here's the question to the group:

should i bite the bullet and drill the holes? or should i have a shop weld the mounting brackets in place?

LET THEM OPINIONS RIP !!!!!!

[dtw]

How about both?
That's actually what my wrench recommended to me, and is what I plan on doing with my project car (I've got the 4 point bar as well, with 4 bolts per point).

[Dug89]

Welded or mounted, the important part is the size of the pads. You want the spread the surface of the pad over a large area. The floor sheet metal is thin and you do not want to punch the cage through the floor if you have to use it.

Welding offers secure mounting although welding a thick pad to thin chassis has its challenges (blow through the sheet metal of the chassis).

A bolted cage offers you the luxury of adding a mounting plate on the bottom of the chassis, sandwiching the chassis sheet metal.

I would weld if the cage footers are large (surface area). Bolt if you can add a backing plate.

Don't kid yourself thinking that with a bolted cage, you have the option of removing the cage. When you see how hard they are to get in, you won't remove it.

Happy Caging.

[tobluforu]

If you have the option, do what dtw suggest and do both. I have the same bar and it's bolted. The hell if i'm ever going get take that thing out. Was a ***** to get in. I also added larger plates on the underside of the pan like doug89 suggests.

[dtw]

Whoops, yes, I forgot backing plates! Suggested in either event; welding or bolting.

I'm getting rather close to this step on my car now- suggestions on thickness of backing plate?

And not to get too far off topic- y'think I can still install a headliner and tensioning rods with a rollbar in the way?

-d

[Laura-Hergesheimer MotorS]

Weld. Pull up carpet, weld plates into place, weld bar to plate, make slit in carpet, put carpet back down. Later when you want to remove, cut off bar at plate, put carpet back down, no damage was done, no extra holes....

Bolt in bars are not always the most economical and least destructive to an interior as advertised. Reality is most bolt in bars are put in and they stay in, just too cumbersome to keep taking in and out per event. Granted you can't use the back seats other than for storage....

Laura
Hergesheimer MotorSports
Lake Forest, CA

[StuttgartDavid]

Backplates are key to strength and safety (in fact, they probably make welding redundant). But I wonder if they have another use, i.e. reinforcing the chassis further:
I note that the Autopower cage doesn't have a knee level bar connecting the front legs as do many quality custom jobs. Ideally, to minimize flex, the two front legs would be connected near the floor pan. Well, how about under the pan via the backplates, since you're already adding steel there? While you're at it, why not run up 12 inches and tie the backplates into the front A-arm/steering cross piece? How about the rear backplate tied into the Rear torsion bar tube anchors, or extended to the motor mounts on the torsion bar tube itself? (Yes, I know, while not a "thru the bulkhead" brace, this could still trigger rules issues due to tying into the suspension, but from a stiffening standpoint wouldn't this really help?) Anybody done it, or have any good structural engineering thoughts here?

[Laura-Hergesheimer MotorS]

The comments by David above are why most of the time after looking further, a custom fabricated partial cage for your safety needs can be more economical and feasible. Look ahead to where you want to go with your car and try to spend your money once.

Laura

[tobluforu]

dtw, I had the headliner replaced with the autopower bar still in the car. The guy who did it said he had no probs. Not sure if you have a full cage or not.

[jluetjen]

tmctguer;
You never mentioned what your intended use for the car/bar is. Looks? Soloing? Occasional DE events or first steps to a full-time race car? Each would result in a different response. Here's my broad-brush response:

1) If it is for looks, bolt in is fine. Backing plates should be used to get any benefit at all, but don't expect it to add much safety in a major crash.

2) Soloing? Similar to above. By the way, I doubt that 4-point bars add much rigididy to the car since they don't tie in any of the suspension mounts nor span much of the length of the car.

3) Occasional DE Events? I assume that a bolt-in bar is legal when DEing on a race track. I don't think that I'd feel comfortable with one. Compared to a correctly installed bolt-in cage, you're really not getting that much protection. By cage I mean 6 mounting points with door bars, cross-pieces between the forward bars and a diagonal in the main bar. The mounting plates should meet SCCA spec's: Same thickness as the bars, backing plates of the same dimensions, minimum of 3 bolts per plate. All hardware should be Grade 5 or better with 5/16" diameter minimum. If plates are welded to the car, they need to be > .080". Anything less then this really won't add a lot of strength to the car. My experience is that most accidents at DE events or by novice drivers are unforced and don't involve other cars. But once you've lost the car into the tires it's too late to rethink your safety strategy.

4) Full race: In all honesty, bolt-in cages (6 points) really are minimum acceptable designs. If you intention is to one-day go all the way, you'll want to go with a custom welded cage with at least 8 mounting points because they are attached to suspension mounts and chassis rails rather then the floor of the car. The cost isn't that much different after you factor in shipping costs of Autopower cages and the other incidentals. By the way, I used to have an Autopower in my ITB car and it is a good product for what it is.

Finally: Get >>>good<<< roll-bar padding and put it anywhere that the cage or bar is within 4 feet of you or other passengers. This includes the bar behind you! You only need to hit it once in anger to learn how really hard cold-drawn steel is.

[PorscheDV]

It's your car...do what you want to it...





SORRY! couldn't resist!