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Chassis reinforcement pics, opinions


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I have gathered together a lot of pictures of what people have done to add cages and stiffen the 240Z chassis....

 

Tube frame conversions are too much for my tastes... too much to be streetable... IMHO...

 

Race cages usually don't allow the doors to stay intact and they use "petty bars" that make the passenger seat useless...

 

Bolt in cages and roll bars don't do much to stiffen the chassis...

 

My car is rust free.. so front end/ frame rail replacement is overkill....

 

This is a rough picture of what I am doing....

 

240Zcageplans.jpg

 

 

...

The blue lines are "bolt in" tower braces... the rear has a diagonal to the floor...

 

The green lines are roughly my cage outline... not exactly isometric but close...

 

the red lines are door bars and strut tower extensions... (this is the area I need to decide on)

 

the 2 yellow lines are rocker to TC bucket bars.... ( I would like some opinions on these....)

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Here's a version based on my tube car and what I'd do if I were to build another unibody car. I don't have any fancy FEA analysis this was done the old fashioned way by building a model out of welding wire and looking at where it deformed when twisted.

 

chassis.gif

 

My powerpoint CAD skills are a little lacking. The big changes over your original design are a lower X tieing into the strut towers, an X in the roof also connecting into the strut towers in the rear. In the front there's a lower K member and an X that goes from the sway bar mounts to the strut bar.

 

In my basic models I just had a flat floor. I was only looking for changes in stiffness in the cage figuring anything I did that made this more stiff would translate to a stiffer car. In real world testing hooking the cage into the windshield frame and adding gussets around the windshield frame helped a lot with torsional strength. In my opinion the rockers in a Z are really weak and I'd reinforce these with tubing.

 

This isn't the end all be all by any means. I hope it helps to spark some discussion.

 

Thanks for the photobucket tip

Cary

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A couple suggestions:

 

1. Add a knee bar under the dash connecting the front cage downtubes. This helps prevent the front of the pan and the door bars from crushing in a big side impact.

 

2. Reinforce the front ARB mounts.

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I like the ideas for the roof bracing work... that really makes the roof work for me to stiffen the strut towers... Can I do that with smaller tubing?

 

I am using 1.5 .095 DOM for the main tubes... what would you use for the gussets and bracing...????

 

 

The ARB mounts are a part of my plan... obviously most folks go from the tower >>forward and down to reinforce the sway bar mounts... though Tube80s plan seems interesting....

 

Tube80s plan would need to be removable in order to allow engine installation... Tube80??? have you run a string along that path with a 1st gen SB350 in place????? the other thing is that the center crosspoint is in empty space... Is that a problem????

 

 

I like the idea for the rear (black lined X brace)... but is that redundant considering the sheer number of panels and frame rails involved in that area already...???

 

The K-member is a great idea... especially combined with tying in the rocker tips.... but does it allow the exhaust sytem to exit the engine bay??? I'm just concerned with access.... have you tried it before??? was it removable?

 

John C. thanks for the chime in... I will be ordering a FG rear hatch from you for this project... Are you speaking of adding a second bar crossing below the dash and steering column...???

 

there is a dash bar in my plan.. but it is weird... I am trying to make maximum use of the original torque box in this area.... Most of you won't like it... but I am pretty fond of my bent dash bar...

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I overpurchased tubing for this project... I still have 2 uncut 22' sticks of 1.5" .095 DOM on the rack... I have plenty of 1.5" square tubing... I also have some 1" sq. tubing... I have a box of 50 preformed "taco" gussets...

 

The problem is that it all weighs 200lbs...

 

Keep in mind that I am using this car for Time Trials and track days... I only need a rear hoop with one diagonal and 2 supports... the rest of the cage is to maximize the stiffness of the car... and make my wife feel better....

 

I just got my instructor certification this year and I plan to make maximum use of it... I get a lot of seat time... but I am not at great risk of side impact collisions... rear impact seems most common... front end into Armco would be a worst case situation...

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I like the ideas for the roof bracing work... that really makes the roof work for me to stiffen the strut towers... Can I do that with smaller tubing?

 

I am using 1.5 .095 DOM for the main tubes... what would you use for the gussets and bracing

 

In my car the roof bracing is 1.5x0.049 tube. You could also use 1x0.065. I stole that idea from a DTM cage design I got pictures of. I've seen in a few other cars as well as a PDF for a NASCAR FEA study.

 

Most of the general non-cage bracing could be 1.5x0.65 and the guesets could be 16 guage. On my car the lower X is 0.065 tube. I use an X brace in the rear hoop along with this to help in side impact.

 

The ARB mounts are a part of my plan... obviously most folks go from the tower >>forward and down to reinforce the sway bar mounts... though Tube80s plan seems interesting

 

What I have is a little misleading. It would also have the tower braces down to the swaybar mount' date=' which is missing in the pic. The rest of the structure, which would probably be something like 1x0.065 tube would be a bolt in.

 

Tube80s plan would need to be removable in order to allow engine installation... Tube80??? have you run a string along that path with a 1st gen SB350 in place????? the other thing is that the center crosspoint is in empty space... Is that a problem

 

Yes, it is removable. Take a look at a viper competition coupe and you'll see some of where the inspiration came from. The rest was how to close the large open box teh Z has for an engine bay. I'm not a big fan of tieing into the cowl as most people are. I'd rather hook to the corners of my cage, which I believe would make it all stronger.

 

If you do hook to the cowl I think creating an X with bracing down to the sides of the tunnel where the transmission mounts wouldn't hurt. My old GT/FP car had a tube that ran from the back to the front to brace this area.

 

I like the idea for the rear (black lined X brace)... but is that redundant considering the sheer number of panels and frame rails involved in that area already

 

Perhaps, but it was light and made major improvements in my model. And in my tube car I have no structure here. If you decide to go nuts you could remove a lot of teh structure and let the tube take its place. I have a taxicab bulkhead in my behind the seats. If I was doing a track day unibody car I'd do this to keep the hatch area from becoming a parachute.

 

The K-member is a great idea... especially combined with tying in the rocker tips.... but does it allow the exhaust sytem to exit the engine bay??? I'm just concerned with access.... have you tried it before??? was it removable

 

I had a similar brace on my car that cleared the exhaust. It was removable. If you use a heimed TC rod mount you could box the bottom of the TC area and use this to bolt this brace to.

 

Cary

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I am using 1.5 .095 DOM for the main tubes... what would you use for the gussets and bracing...????

 

1.5 .083.

 

I like the idea for the rear (black lined X brace)... but is that redundant considering the sheer number of panels and frame rails involved in that area already...???

 

You need some kind of a diagonal brace in the rear hoop to keep it from racking in a roll over. A single diagonal within the plane of the main hoop is what SCCA requires. FIA regulations allow an X in the rear braces.

 

Are you speaking of adding a second bar crossing below the dash and steering column...???

 

Yes. You don't need one up high because of the cowl box. You'll just be adding weight. You need one down low that crosses on top of the trans tunnel. Adding a plate and connecting it to the trans tunnel is a good idea. You can also run the knee bar forward at an angle and connect it to the firewall where the trans tunnel and firewall meet.

 

The purpose of this bar is to keep the front legs of the cage from bending inward as the floor buckles in a side impact. You are trying to spread the loads of a side impact to the other side of the car via the cage. The area between the rocker and trans tunnel in front of the seat mounts is weak and a side impact tends to buckle the floor pan - crushing feet and legs.

 

BTW... the low doors bars you have in your design need a knee bar to keep them from crushing inward in a side impact. Personally, I won't install those kind of door bars in a customer car unless there is a knee bar as part of the cage.

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A single diagonal and a harness bar are part of the design.... It sounds like I could remove the single diagonal and trade for the x to the strut towers.... ????...

 

the knee bar is something I will have to look into... I'll pull a string today and see what I can do with it...

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I don't have a cage, I just have a roll bar at the moment. http://forums.hybridz.org/showthread.php?t=102715 I'm still considering going with the full cage. Cary's been trying to talk me into it, but I'm not sure just because I'd have to pay someone to do the front bends just like I had to pay for the main hoop. The hoop and material to do the bar ended up running about $350 and the front would be considerably more complicated, so I'd have a lot of $$$ into this thing by the time I got it all done. Plus I already have the roll bar welded in, so I'd have to either drill holes in the roof to weld in the front part to the main hoop, or I'd have to cut the roof off, weld the tubes, and then weld the roof back on. Either way is kind of a hassle, and I still have so much other stuff to do that I'm not sure I want to deal with it. I'm torn because of the weight issue, and John only had a bar in the ROD, but then there is the impact protection of the cage, cost, time, weight, etc.

 

I don't like your door bars as shown in this thread though. I'd attach them to the down bars in the front and the main hoop in the rear. I thought you had another design where they were going to bend down and meet in the middle, kind of like >=< I thought that looked like a pretty stout design.

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well... that is still an option.. though I was hoping to make a more simple design that allowed easier access....

 

My thought was that the design I have at the top of the page would still give me stiffness at the expense of being actual door protection bars... I would not want to make it anymore dangerous... but I was trying to be minimalist here and really focus on stiffness more than protection...

 

I strung up the beefy x bar path on another car... man that is going to be a pain to get in and out of...

cagedrawing.jpg

 

 

...

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Here are some examples of what I have found around...

 

 

 

This is a pretty car... nice execution...

but the door bars dont look like they meet all criteria...

ex5.jpg

 

 

 

 

This one look like it would pass tech.. but does it really stiffen the chassis...????

ex6.jpg

 

 

 

 

 

I think this is Darius at work... he builds some mean machines....

ex1.jpg

 

 

 

 

 

 

This looks like an example of the cross brace in back... I pulled strings.. this is what you get...

ex8.jpg

 

 

 

 

I was told that SCCA want's 2 door bars in competition.... an X welded in the middle is considered one bar...

2 "V" shaped bars gusseted together are still considered 2 bars....

 

I guess that is what i'll be doing.... it's just that most folks dont do this.. even in race chassis...

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I was told that SCCA want's 2 door bars in competition.... an X welded in the middle is considered one bar...

2 "V" shaped bars gusseted together are still considered 2 bars....

 

I guess that is what i'll be doing.... it's just that most folks dont do this.. even in race chassis...

 

You mean something like this:

x-door.jpg

 

I've seen a few of the WC cars setup like this. On my tube car the bars will be done like this but will be out into the door. More of a pyramid shape.

 

Cary

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No, but I have pics of my own bar there: DSCN1199.jpg

 

Here's my cage design that I am mulling doing.

cagedesignjm.jpg

Yellow= original frame or crossmembers (with the exception of making the front crossmember into a K member)

Red = SFC or miscellaneous braces

Blue= strut tower braces

Green = cage

 

The red at the front is an X that will go in the core support. Still trying to decide exactly how to do that one.

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