More Cab Stiffening

[widebody911]

Ok, I've had this idea of making a door brace for my cab for a while now. The other night I did a mock-up with a couple of 2x4's across the opening to test the ingress/egress issues. 4" of occlusion is about all my size 15's can handle without removing the steering wheel.

So on a whim, I ordered some 1 1/2" CroMo tubing - it should be here later this week.

But today I was at the local scrapyard, and found 2 1/4" CroMo tubing cheep - $3 for a 5' section! It's bigger than I wanted, but I just couldn't resist. I also bought some 14ga sheet metal to use as a backing plate, if need be.

Here are two candidates for the design: I like the first one, which runs parallel to the sill, because it seems to be the least obtrusive. The angular version might provide better stiffening. It wouldn't be as high as shown in the pic, but you get the idea.

Feeback welcome.

[Chuck Moreland]

Angular will provide the most stiffness. And there is nothing gained by the larger diameter, except weight.

Perhaps you should try the box section stiffeners first. Completely unubtrusive and you may be satisfied with the improvement.

[jester911]

The best way to make a cab stiffer is trade it for a coupe

[BGCarrera32]

I sort of agree with Chuck, but in order maximize the reinforcement you have to get as high as you can on the B pillar behind the seat and as high on the A pillar as possible. In order for the second drawing to do any good, you're gonna be climbing over the brace everytime you get in the car (PITA). How bout a truss type setup...this is something you could make out of 1/2 or 5/8" thick 6061 aluminum plate or perhaps 7000 series if you want ultimate tensile strength and twist resistance. You could cut this out with a jig saw (sabre saw) and a carbide bit if you were patient (or a CNC gantry mill ). Weld some big nuts to the pillars or leverage whatever bolts are available, and have through holes at the mounting points on the truss for the bolt up. The idea I sketched is that the big curves front and back transfer stress to the center of the truss while allowing the mounting points to get as high as possible on the pillars to create a strong box section. Mucho lighter-mucho stronger if done right...

I dunno...just a thought...

[widebody911]

First off, thanks for the replies so far.

I fabbed up a prototype, using the 2 1/8 (not 2 1/4) tubing 'cause that's what I had on hand. I figured the worst I could do would be to waste $4 in materials This piece weighs just a tad over 4lbs

For more pix, go to http://66.34.72.138/howto/door-brace/index.html

[Langers]

Thom,

Have you thought about just putting a whole cage in there? Would solve any roll-over protection worries at the same time as making your car at least as stiff as a coupe.

[widebody911]

Originally posted by Langers
Thom,

Have you thought about just putting a whole cage in there? Would solve any roll-over protection worries at the same time as making your car at least as stiff as a coupe.

Sshhhh! Don't tell anyone, but I'm still pretending this is a street car!

[Bill Verburg]

Thom, I gotta agree that you ought to get a coupe for racing. Use your car for what it is, a very nice street car for sunny California.

I made that decision a long tine ago for my Targa.

[Tyson Schmidt]

Originally posted by Bill Verburg
Thom, I gotta agree that you ought to get a coupe for racing. Use your car for what it is, a very nice street car for sunny California.

I made that decision a long tine ago for my Targa.

SILENCE BLASPHEME!!!!!!!!!!!!!!!!!!

Thom, I think it would be cool to have a partial cage built that used simply a hoop that ran across the underside of the dash, and connected the front of the inner rockers. Then, using removeable side bars just like what Jack has in his car, that would bolt to the roll bar in the rear, and the under-dash hoop inthe front. It would stiffen the car immensely, and greatly increase side impact safety. And you could remove it in 5 minutes time when you aren't at the track.

[widebody911]

Originally posted by Bill Verburg
Thom, I gotta agree that you ought to get a coupe for racing. Use your car for what it is, a very nice street car for sunny California.

I can't dispute the fact that a coupe would be a better racing platform, but aside from the fun of mechanical masturbation, there's a couple other issues:

• I don't have Olsen-esque resources to throw at the project
• I just squandered a good chunk of my savings on my garage project which would have bought me someone's divorce-sale track car.
• I could swap all my bits over to a coupe, but what would I do with the shell?
• I'm learning a lot about the structure of the 911 from this project.

[masraum]

Thom, personally I think the horizontal bar will be better than the diagonal since the diagonal will put all of the body flex at the front edge of the door opening rather than being distributed across the openning threshold.

[Bill Verburg]

You can't make a silk purse out of a sows ear no matter how much $$ you throw at it. I guess you can make a fast sows ear though.

Just my opinion. I decided to buy or build a proper race car.

SCs get to be 100# lighter in 2004

[widebody911]

Originally posted by Bill Verburg
You can't make silk purse out of a sows ear no matter how much $$ you throw at it. I guess you can make a fast sows ear though.

What's funny is that is exactly what I tell the VW kids that ask me about putting big type IV motors in their bugs and busses - I tell them to buy 911s or 914's

[5axis]

Proving I should stick to CAD CAM. Here is a very bad sketch starting with a stable cage. My thought was/ is to add a few more mounting plates to better tie the body to the cage.

what ya think?

[JeremyD]

I say weld the doors on and get in and out like Batman.............

[island911]

Originally posted by Chuck Moreland
Angular will provide the most stiffness. And there is nothing gained by the larger diameter, except weight.
. ..

I dont agree.

First, the "Angular will provide the most stiffness" ONLY if it goes diagonally, both ways (which it doesn't in this example) or hits much higher in the front.

Secondly, the (heavier) larger diameter WILL add longetudenal stiffness. . .just not as fast as the picking the right points (it will add in a more linear fasion.)

Third, the larger diameter will add some torsional stiffness (albeit a small total addition)

[dickster]

other - i'd go for the roll cage idea.

"weld the doors shut" - with remote window winders!

[Jack Olsen]

5Axis' drawing is a good start -- but if you imagine grabbing the front and the back and trying to twist it, wouldn't a pair of bars on each side do a better job?

My bolt-ins do go in and out quickly. But they're easy enough to get around, so I generally leave them in.



(Click for the big version.)

[5axis]

5Axis' drawing is a good start -- but if you imagine grabbing the front and the back and trying to twist it, wouldn't a pair of bars on each side do a better job?

I would guess it would help?????
Island?




The starting point.
http://stable-energies.com/autopower/autopwr.html

[Mike Kast]

My bolt-ins do go in and out quickly. But they're easy enough to get around, so I generally leave them in.

Mr. Olsen? Where, might I ask, did you aquire that beautiful machine? I mean the cage. I want one!