rollcage guys...advice requested, hideous MSpaint image insi

[Guest bluex_v1]

I just bought a used S&W 240z cage kit for my (early) 260z. After getting it home, its pretty apparent that they must have used a testors plastic model and toothpics to design the cage and just scaled it up or something.

Anyway, I was not at all happy with the placement of the main hoop, so I cut it in two places at the top horizontal bar, just as the bends begin on the upper corners so I could widen it. I placed the feet of the main hoop down into the crevice where the bottom outboard portion of the front of the rear wheelwell meets the upper corner of the seatbelt pocket plate and the back end of the rocker box. I have it welded primarily to the rocker box and the seatbelt pocket reinforcement peice and tacked intermittently to the fender. (I will probably put a square chunk of rectangular tubing up from underneith to strengthen the area it sits over and hopefully tie that to the rear subframe somehow)

To strengthen the sections of the main hoop that I cut in half, I will be running tubes from the main hoop, which will be attached directly under those seams, they then will run down to some beefy brackets that will either bolt or be welded to the upper front corner of each rear strut tower.

I have the halo part cut and positioned as snuggly against the roof as I could get it, and then the front A-pillar downtubes hit the rocker box about 5 inches back from the front of the door opening (works out well that way for my dash plans, and hopefully adds a little side impact protection to keep the door from collapsing completely) The feet of the down tubes are about half on the top of the rocker box, and then I cut a peice of rectangular 1/8th wall tubing in half to connect the part of the tube hanging off the edge down to the floor. This rectangular tubing (really a C channel now) is also welded to the side of the rocker box.

I have a main diagonal running from the top of the main hoop just to the right of the driver's head, down to the floor, inline with the main hoop. At this diagonal's base, it welds to the upper-most part of my 2"x1"x1/8th wall frame rail/subframe connector. This diagonal is at about 60 degrees inclination from the floor, which is about as shallow as I could get it without it getting in the way of the seat backs. I also have a shorter diagonal running at the same angle, intersecting that main diagonal at the center line over the trans tunnel, and running down to the driver's side framerail/connector.

The following stuff I have not done yet, but are my plans:

As I said above, tubes running from under the main hoop cut seams, down to brackets on the strut towers.

Run a diagonal from the drivers side strut tower bracket, up to the passenger side upper corner of the main hoop where the other strut tower tube attaches.

Run a diagonal from the drivers side of the main hoop where the first bend starts at about shoulder height to the driver maybe, horizontally back to the passenger side strut tower bracket.

 

Also, How much would a pair of horizontal bars on each side, just barely above the top of the rocker box, running from the main hoop to the front downtube help to stabilize the chassis? I'd probably have to raise it so high to clear the door handle and stuff that it'd be too cumbersome for daily driving though. But if it would be an absolutely significant improvement, I might do it.

 

If it doesn't load

 

A - main hoop feet attaching at back of rocker box and top corner of seatbelt pocket plate.

B - diagonals attaching to tops of rectangular frame rail/sub frame connector tubing.

C - Strut tower brackets

D - A-pillar downtubes attached to top of rockerbox and C-channel reinforcement welded to side of rockerbox and floor.

 

How many holes do you guys see in this structure? what would you suggest. My goals are chassis stiffening, saftey, minimal visibility obstruction, and finally, minimal driver compartment encroachment. Any criticism, no matter how minor would be appreciated..this is my first car project, and my first rollcage...I don't want it disintegrating and skewering me if the excrement impacts the rotational ventilation device.

Thanks

[ZROSSA]

Blue X,

Hear is what i would do. Keep in mind that you never want to put a load into the middle of a bar.

 

Take out the short B

 

Take out the bar from C to the centre hoop.

 

Join C To C. make sure its tied into the rear struts.

 

Join C to D. This may not work in practice do to space and the need to get in and out. lower the join on a to make it as easy as you can to get in and out.

 

If you can go through the fire wall to join the front struts then you will have a very stiff structure.

 

One other thing yo might like to consider is to join the diaginal that goes from the main hoop to the rear struts might be better if it is the other way around, Going from the drivers head to the right rear strut. Im not 100 % sure this is better then what you have and if its already welded I wouldnt bother, But its seem to triangulate (sp) that area better.

 

Good luck,

 

Douglas

[Guest bluex_v1]

Well I do want to keep the short B bar so that both frame rails/connectors are all joined with the cage...The only thing I see that might bend that longer diagonal due to the short B would be force near the driver's head, pushing down and toward the right side of the car...if that is true, what if I gussetted the joint with a pair of plates on the driver's side there? Are there other things I'm missing?

Also I could turn that into an X with just another peice from the middle joint up to the passenger's head...that way the main hoop couldn't really fold over either direction.I think?

[ZROSSA]

Howdy,

 

Go for the full x bar then. That will make it nice and stiff. As you have it drawn it doesnt do much.

 

Douglas

[johnc]

Jeez! Cutting the main hoop basically makes the roll cage illegal for SCCA, NASA, NHRA, IHRA and pretty much any race sanctioning body. Hopefully you were not intending to do any formal racing with the car.

[Guest bluex_v1]

I did check the SCCA site, but all I could find was a place to send money in order to get their rule info...I shoulda asked here first. Well I'm only intending this for a fun daily driver...but was hoping I might do SCCA time trials or something eventually. Oh well, too much work ahead of me to worry about that now.

[johnc]

For SCCA you have to purchase their General Competition Rule (GCR) book because their rules require that you have it in your possession at the track whenever you race.

[Mike kZ]

Are you planning on using a harness? If so you need a bar between the main hoop to attach your harness.

[ZR8ED]

Since the car will not be formally a race car.. you can do what I did to mine.

 

Mine is not a racecar either, so technically my cage would not be legal either.. but when you cut a pipe and want to widen it (like I did to get such a tight fit to the roof.) Insert a smaller diameter pipe inside the pipe where you cut it... say a few inches and leave a few inches sticking out. Weld it all around the seam. ( from small diameter pipe to lip of larger pipe) then simply slip the other side of your hoop/pipe/bar over the smaller pipe that is sticking out, and weld it up. We left a gap between the two larger diameter pipes (1/8") and left that gap to weld the two larger pipes to the smaller diameter pipe that is now inside the two halves... makes for a WAY stronger seam.

 

You guys follow that? hard to type in words...

[Guest bluex_v1]

Mike, I am not planning to use harnesses any time soon...which is one of the main reasons I opted to cut the hoop in the first place so it didn't occupy the lower seatbelt pockets. As I'm sure you know, driving through Atlanta traffic and not being able to lean forward to get good looks out the rear corners to check blind spots could be a problem.

zr8ed, what you described makes sense. I should have done it that way...but impatience got the better of me. I'm thinking that since this tubing is about 1/8th wall, and having the seams supported by those tubes down to the strut towers, I should be fine as far as saftey is concerned. I may redo it after I get the more important things like brakes done so I hopefully won't have to test out its strength.