roll cage

[Guest Maxwell]

anyone have any shots of there roll cage they could post? I'm working on welding in my floor pans, and would like to build a cage in at the same time. Just looking for where you would tie it in behind the seats... looks like a tight fit.

 

Thanks

Maxwell

[Tim240z]

There are some pics on my site. It's a S&W kit (8 point)

Tim

[Dave]

All kinds of pictures at http://12.224.138.56:8884/Files/Datsun/Rollbar/

[Guest Maxwell]

Thanks guys, thats perfect!

 

Max

[katman]

Perfect? Did you want a cage for looks or a cage for safety? Is there a particular type or class of racing you're trying to meet or just for street?

[stony]

katman you seem to know what your talking about... im about to order a Chris Alston 10 point cage for my z. I dont plan on doing any "real" racing but would like to have a cage that is legal in IHRA and NHRA (just incase in change my mind about teh racing thing) and stiffens up the car and also adds safety in case of a crash. any suggestions?

[Guest 400 ci 280z]

i also was wanting something that is IHRA and NHRA legal too. thanks

[DemonZ]

Katman, how about telling us what would make a good cage instead of what would not

[Boobala]

The guys in the link below make both 8-point and 10-point roll bar/cages for 240Z's.

 

http://www.swracecars.com/rolbarlist.html (scroll to the bottom of the page)

 

http://www.swracecars.com (the home page)

[katman]

Originally posted by hooptieZ:

Katman, how about telling us what would make a good cage instead of what would not

Well that depends somewhat on the application. If you are racing in a particular organization then you obviously have to meet their rules (SCCA, NHRA, HSR, whatever), which may or may not meet other criteria like safety. But some things to consider:

 

If I was doing a "cage" for a street car only that did autocross and some track days with a sanctioning body or club which required a rollbar but didn't require a full cage, my primary goal would be safely mounting a 5 or 6 point belt system and keeping the weight to a minimum so as not to influence the rollover and handling characteristics of the car. Keep in mind most of the material in almost any cage or rollbar setup will be above the vertical CG of the stock car, so a cage hurts handling to some degree (not to mention acceleration). Also, ignoring the mass (which I personally cannot), almost anything you do will be better protection than the stock car unless it's design is just so bad it adds elements to the interior of the car which will actually hurt you instead of help you (not out of the question BTW). I'd use 1-3/4 OD by 0.095 wall DOM tubing between the rear strut towers to loop the belts to, and put in a short main hoop as far outboard as I could get it mounted to the forward side of the rear wheel well. I'd put in a horizontal in the plane of the main hoop at shoulder level for the belts to ride over, and a short section on each side from the top outboard corner of the main hoop back to the strut towers for some stability. This setup provides almost no additional rollover protection from stock (no diagonal in the main hoop plus the wheel well deforms), no additional side impact protection, but is light and stable for mounting belts to keep your arse in the seat for autocrossing and having fun.

 

For actual crash safety for street or racing you should build to SCCA rules. Some elements of a safe design for the 240/260/280 unibody would be (assume all tubes 1-3/4 OD x .095 wall DOM mild steel, all attachments to the unibody have .120 plate):

 

1. Main hoop at the bottom intersects the rocker beam at the wheel well and is gusseted vertically to the wheel well (which shears the load to the vertical beam at the end of the tranny tunnel. Wheel well can take shear but not a punch load like in my street hoop). The mounting plate here has to be formed funny because there's several surfaces of the unibody that come into play here, it also covers up the seat belt mounting hole so that has to be drilled out ahead of time. The tube does not go to the floor, it sorta runs out in the rocker. At the top the main hoop is just forward of the trim piece that contains the interior light. Just under the rear quarter window there's a boss in the unibody for a tooling hole or interior screw (can't remember which). This is where another slight bend occurs so the hoop can follow the contour of the car. The main hoop should almost touch this boss, like 1/2 inch clearance at most. The main hoop will have an uninterrupted diagonal from the top just above the drivers right ear (just inboard of the end of the radius for the upper left bend) down to the intersection with the rocker or floor on the passenger (left) side. Then you need a horizontal to stabilize the intermediate bend at the aforementioned boss and the main diagonal, from one side to the other split at the main diagonal. Need one more horizontal at the top of the tranny tunnel to stabilize the bottom of the hoop and help get side impact loads to both sides of the car at once (load distribution). The cages that run a diagonal into the tranny tunnel may as well stop them in thin air because the tranny tunnel not only folds up if you try to push on it but it also usually splits in a big T-bone type accident. For SCCA you'd also need to integrate the seat back and headrest supports in here somewhere. You can make a cage heavy enough to not collapse in a rollover without using a diagonal, but it's stupid.

 

To support the top of the main hoop in a fore/aft direction for the case where your rollover also involves an element of fore/aft motion (which is basically always), I run a tube from the middle of the upper main hoop bends to the strut towers as far outboard as I can get them, and then a horizontal tube between the strut towers (if rules allow, in SCCA ITS they don't so I weld a tube to the two previously mentioned). Better would be tubes from middle of the upper main hoop bends all the way back to the taillight area, brushing the strut towers along the way, but I haven't had need to do it this way lately.

 

2. Door bars. An "X" gets you more torsional stiffness whereas "NASCAR" style mutiple tubes bent out into the door skin gets you way more T-bone protection. What happens at their forward connection at your feet is critical to either one being anything other than the waste of good tubing. The floorboards and the stock unibody's ability to shrug off a T-bone in the vicinity of your knees is this car's weak point. Cages with a forward down tube (the one that runs along the top of the windows, down along the A pillar, and to the floorboard near the door hinge area) which attaches to the floorboard only nearly always punches thru the floor in a rollover and ALWAYS collapses into your shins in a side impact. Z's are just wimpy here. The forward down tube should blend into the rocker panel at the forward opening of the door. This keeps it out of the way of your dead pedal. Too far forward encroaches on that. The forward down tube has about half of it stopping on top of the rocker and the inboard half continuing to the floor. Nice big mounting plate here integrating the rocker and the floor. Carry a tube to the firewall from the forward down tube running just above your toe when it's on the dead pedal. Shuold hit the intersection of the vertical portion of the firewall and the slanted portion (important). Now then, you need a horizontal about 1/4 inch above the tranny tunnel from one downtube to the other (if rules allowed I'd gusset this horizontal to the tranny tunnel). This helps distribute the side impact again to both sides of the car to spread out the loads. A horizontal tube above the dash is another waste of tubing (because the downtube just folds inward from the doorbar loads with the horizontal up high). Of course lots of padding on my tube or you'll break your shins. The key is to get the side impact loads into the firewall on their way to the engine (the big mass providing the M part of F=MA) at the same time maintaining the integrity of the capsule where your feet and legs are. As a point of interest, a Z will tend to split the floor and tranny tunnel right about your right thigh and hip and I've seen collateral damage (injury) from this before. Hey Pete, they split on a 45 degree angle more or less just like the classic shear failure!

 

A single tube serving as a door bar from the main hoop down to the floor will just fold up the floor without all this other stuff relating to the forward down tubes. Not that that's any worse than stock, it's just not significantly better.

 

Now you have a foundation for the door bars. Maybe a later discussion, have to get back to work.

 

As I've said before, a good description of the load paths (what causes the loads and where they want to go to be reacted) with pictures of a good SCCa type cage is in an old Z Car Magazine article on building an ITS 240Z. I can scan this in if there's somebody I could email it to that could post it somehow.

 

Lots more details to work out for a good cage, but this is a start. The S&W and similar cages are NHRA approved I believe and that's why their wall thickness (and hence detrimental effects on handling to some degree) is so big. The Z unibody is the weak link, how any cage is integrated, and WHERE exactly they're integrated is very important for a road race type application. Most of these aftermarket cages will give you a good spot for seat belts (albeit a heavy way to do it) but little else IMHO. Hope this enlightens a bit.

[Pop N Wood]

Katman is already on the hook for giving us the ultimate street cage

 

http://www.hybridz.org/ubb/ultimatebb.php?ubb=get_topic;f=6;t=001382

 

Here is a link discussing the pros and cons of the "ultimate" front brace pictured above

 

http://www.hybridz.org/ubb/ultimatebb.php?ubb=get_topic;f=12;t=000682

 

Here is another choice for front braces

 

http://www.hybridz.org/ubb/ultimatebb.php?ubb=get_topic;f=6;t=001442

 

There are quite a few good options for roll cages and stiffening.

 

Here are a couple of my favorite roll cage-subframe HybridZ threads

 

http://www.hybridz.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=6&t=001099&p=

 

http://www.hybridz.org/ubb/ultimatebb.php?ubb=get_topic;f=6;t=001118

 

http://www.hybridz.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=6&t=001370&p=

 

Here is a good thread about subframe connectors

 

http://www.hybridz.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=6&t=001526&p=

[Pop N Wood]

Whoa, Katman. Our postings crossed. Looks like we are both having a busy day.

[DemonZ]

a picture is worth a thousand words

 

I have to reread some parts several times and I still don't know if I got the picture

 

I hope someone can host the article soon.

 

Thanks Katman.