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#1 redneck1545

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Posted 22 August 2011 - 04:53 AM

Im copying 74_5.0_l's cage design and need more advice and pictures on the mounting plates for the door bars to the front floorpan/firewall

Should I build boxes just like the typical roll bar boxes and then mount the angled door bar to it or should I just plate the floor to the rocker and then mount the bar straight to that?


Everyone I've seen with boxes for the front mounts has down bars and a halo or something similar. I dont want to build a full cage since this will be a street car mostly.

Everyone that just has a plate for these bars are constantly bombarded with comments that predict the door bar punching through the floor in the event of a crash.


So Whats the right thing to do? build boxes in the vertical plane and attatch an angled bar so as to achieve some shearing forces or build a box canted at the same angle as the bar so as to achieve direct force in the event of a crash?

Orrrrr just plate the thing like crazy and tie the plate into the rockers???

Ideas?

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#2 johnc

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Posted 22 August 2011 - 07:15 AM

IMHO, the issue with unsupported door bars is that the front mounts will move inward in a side impact. If you can build a low front hoop under the dash up to the bottom of the windshield and run a knee bar across to the door bars on the opposite side you'll have a much safer install.
----- John Coffey, Fabricator at Benton Performance, LLC

#3 redneck1545

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Posted 22 August 2011 - 09:48 AM

I'll look into that option. Got any pics of what your describing?

Going back to the issue of mounting, which option would be better? vertical boxes or cambered(angled) boxes or plates?

I was actually you'd be the one to chime in on this subject!

#4 johnc

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Posted 22 August 2011 - 10:38 AM

The box mounting is up to you, but be sure to tie in the rocker and the floor pan with the box. Ideally you create a low hoop (just like the main hoop) that fits behind the dash and runs as high up toward the bottom of the windshield as possible. Your door bars tie to that hoop. You can also add a knee bar running across the car just below the steering column. The idea is to transfer side impact load across the car to the other door bar mounts.
----- John Coffey, Fabricator at Benton Performance, LLC

#5 johnc

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Posted 22 August 2011 - 10:44 AM

Here are some pics. In this Miata cage example the knee bar is up high and its where I suggest you run the top of the low front hoop I mention.

Posted Image

Posted Image

You can also runt he forward braces and shown in the pics.
----- John Coffey, Fabricator at Benton Performance, LLC

#6 JMortensen

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Posted 22 August 2011 - 11:15 AM

Dan's cage is basically like an older convertible cage, or an open wheel car cage. It's great because you don't have bars where your head is likely to hit them. If you look at open wheel/convertible cages, the idea really is that if the car flipped, the car should sit on the main hoop and the front cage structure and the driver's head should be clear. I don't know if that is technically possible with a Z because the roofline is so low. There's no doubt that it's better than not having a roll bar or cage at all, but if you took a really bad hit right to the roof at the windshield area, there is the possibility that it could still get you. Again though, with a street car I think this is a much better risk to take than putting in a halo and possibly smacking your head on that in a minor fender bender.

Jon Mortensen, owner/operator www.petdoorstore.com


#7 redneck1545

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Posted 22 August 2011 - 06:03 PM

Thank you John and Jon. Thats some really good advice! I think I'll have to end up doing a hybrid of what dan has.

I just found out that he has vertical bars running forward of the firewall and that has other bars that tie into the subframe and strut tower.

I dont know if I wanna do all that considering has basically has a tube front end. What do you guys think about building vertical boxes for the floor and then attatching a vertical bar inside the cabin to the box, then attaching both door bars high and low to the vertical bar and have a horizontal bar running under the dash to the other vertical bar??? Basically what Jon has pictured with the miata cage without the halo or a pillar bars. basically a mini hoop made from straight bars i guess. Would that be safe??? I'm pretty much thinking the same design jon has except inside the cabin without tying into the front frame rails.

I'll try to get pics up of what im talking about tomorrow sometime.
I just think my idea would have no bottom side support as the vertical bar would act as an arm and have leverage in the case of a low frontal side impact.

My main concern is to attach the door bars in such a way that they wont rip through the floor should a roll over or side impact occur but also not have the extra mini front hoop, or halo, or a pillar down bars.

is this possible? I've seen people do this type of install with 6 point cages but considering im not going to be racing in any particular class I really dont care to "adhere" to rules but im smart enough to know "rules" are there for a reason and are usually the safest option. I just want to avoid what was mentioned above with the fender bender brain blender halo bars!!! ;)

Edited by redneck1545, 22 August 2011 - 06:09 PM.


#8 redneck1545

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Posted 23 August 2011 - 06:50 PM

So this is what im thinking...
I know I suck at drawing in paint but the idea would be to plate in the floor to the rocker and then put a plate up under the dash. Attach a vertical bar (in red) running from the floor plate to the dash plate.

Then take the two door bars (yellow) and attach them to the vertical bar. For added side impact strength I would run a high horizontal bar across the underside of the dash (blue) connecting the two vertical bars.

I know it looks like the door bars are an equal "X" but I want to copy dan's design and incorporate the low front bar to make it easier to get in and out of the car.


My only worry is that the bottom bar will not have any side resistance in the event of a low frontal impact, or the attachment points on the dash will not be strong enough to properly distribute the load through the chassis. Is this concern warranted and should I rethink my approach to attaching these door bars? Or should my idea sufice?

Suggestions and solutions are welcome!

Thanks

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Edited by redneck1545, 23 August 2011 - 06:58 PM.


#9 JMortensen

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Posted 23 August 2011 - 10:19 PM

I would do a front hoop (single tube bent like the main hoop, but maybe just 2 bends instead of 4) as high as possible, then attach the door bars to it. I'd run it through the firewall to the strut towers too or at least to the firewall with a big plate top and bottom, but that's me.

In your picture you have the driver's side going all the way to the firewall and the passenger's side going to the door opening. Welding around the tubes at the firewall isn't going to be easy. It's a lot easier to weld them near the door opening, then do another bar forward to the firewall, or maybe two, one on top and one on bottom. Would give a little foot protection too. Running to the strut tower would be better for foot protection, but it's kind of a pain in the butt.

Jon Mortensen, owner/operator www.petdoorstore.com


#10 johnc

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Posted 24 August 2011 - 07:28 AM

Looks fine to me and what Jon says above regarding welding it being a complete pain in the ass. A small, flexible swan neck for your MIG welder helps a bunch. A mirror also helps but practice welding using a mirror before actually trying it in the car. Its ass backwards and you need to get it right the first time.

EDIT: You can also make a bolt-in connection or stub to the forward hoop. All the welding can be done on the bench and then you bolt the forward door bar to the stubs after welding in the hoop. After bolting, you can even run a partial bead around the easy to get to sections. Its still considered a bolted connection so use Grade 5 or higher 3/8" fasteners.
----- John Coffey, Fabricator at Benton Performance, LLC

#11 JMortensen

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Posted 24 August 2011 - 01:42 PM

Or you can cut a bunch of holes for access, then patch them when you're done.

Jon Mortensen, owner/operator www.petdoorstore.com


#12 redneck1545

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Posted 24 August 2011 - 05:48 PM

I dont think I can do the front main hoop design as it would require me to take the car to an overpriced race shop (once again) and be charged for work not completed. ie- they bent my main hoop, quoted me 150 for the hoop then when i show up to pick the car up an pay they have a 400 dollar bill waiting on me because I they "had" to build boxes to mount the main hoop to. They ended up not welding the bar to the boxes afterall but still charged 400 for the work.

So I'm trying to take things in my own hands and have had problems finding reasonably priced and honest shop around the area to properly bend this thick tubing for me.

Since the main hoop is not an option currently I think I will just add the vertical bars and the horizontal bars as pictured ( at the door jambs of course).

Is it really that big of a difference between one mini front hoop and one created from straight tubing to make the front hoop?

If so I probably will eat the extra cost of having one made in the intrest of safety.

Thanks again

#13 JMortensen

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Posted 24 August 2011 - 07:55 PM

Dan has his front "hoop" setup welded rather then bent, but it isn't the end of the cage, there are more connections to the front suspension and frame rails, etc. I would be wary about welding the corners if it didn't tie into a larger structure. Maybe if you added a knee bar 1/2 way down...

It shouldn't be that hard to find a shop to do the work.

Jon Mortensen, owner/operator www.petdoorstore.com


#14 redneck1545

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Posted 26 August 2011 - 01:47 PM

I made some more pics describing what im thinking about doing.

Even though it is not pictured I will have a bar running from the top of the main hoop drivers side to the bottom side of the passenger side.
Keep in mind I am no expert in paint and im not a great artist.

Things im re-considering

1-instead of tying the main hoop horizontal (mid hoop) braces to the reat strut tower bar (like dan's cage) i was thinking about tying them to the strut towers themselves. more attachment points for the car to distribute loads.
Reason- its a compound notch and pretty dang tricky for a first time fabricator to get exactly right and I dont want to eat up 200 bucks worth of metal over two bars I cant get notched exactly the way I want and more attachment points for the car to distribute loads.

2-running the lower door bars through the firewall and plating and tying them into the front strut towers as well to provide more forward support for the front hoop


Things I want to know-

If I made the front bar as pictured would it pose a safety hazard? The lower door bar will not connect at the upper most part of the vertical bar where the horizontal bar connects in an effort to get the horizontal bar as high as possible and keep the lower door bar as low as possible and thats the "leverage part im worried about, not to mention the front hoop would be nothing more than straight bars notched and welded at 90 degree angles.


Keep the ideas coming as im not wanting to waste anymore metal until I get some finalized opinions.
If I have to have the front hoop made can I get a regular tubing bender to do the job?
I got my main hoop mandrel bent and that was the reason for the difficulty in finding someone to do it for me.

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Edited by redneck1545, 26 August 2011 - 01:48 PM.


#15 JMortensen

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Posted 26 August 2011 - 03:42 PM

Post the pictures without the bars drawn in and I'll give you my take on it. I think you're on the right track with a lot of this, but there's a couple things I think won't work. The bar from the door bar to the strut tower for example wouldn't fit in that location unless you put a bend in it. One thing you could do is an X from the dash bar outers to the strut towers. This is what I should have done on my car. I'd do it with a bolt in outer portion in the engine compartment.

You need a tubing bender, not a mandrel bender. A cheap tubing bender costs about $400. I got mine through www.speedwaymotors.com. A pipe bender won't cut it.

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#16 redneck1545

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Posted 26 August 2011 - 05:08 PM

Ask and you shall receive!

And thanks!!!

why o why couldn't I just have stopped with some subframe connectors, new floor pans and did a normal v8 swap??!?!?!?

This has turned into an all out teardown, strip, sandblast, seamweld, metal fab, rebuild!!!

Dear wallet - I appologize in advance.

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Edited by redneck1545, 28 August 2011 - 02:32 PM.


#17 JMortensen

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Posted 26 August 2011 - 11:13 PM

I would do your main part of your cage from the specified thickness required by SCCA, which I think is 1.5 x .095 (double check), and then I'd do all the additional supports in thin walled tube, like 1.5 x .065. It's not going to save a huge amount of weight, but it adds up over the whole project. If you decide to go with 1.625" though, paper towel rolls fit nicely over that size tube, so you can screw around with notches on cardboard and then trace them onto the tube once you have it the way you want it.

OK, some of this might not translate too well due to the angles, but hopefully it all makes sense. It's basically a very slight modification of Dan's entire setup with the hoop in the passenger compartment, an X to the front strut towers, and the bars from the bottom of the A pillar to the strut towers like my cage has. Also changed are the main hoop supports and bars from the door bar to the hoop; they now meet together in the front of the strut tower. There is a thick metal plate on the top of the strut tower. Weld your mounting plate to that and you should be good to go. Could even wrap up over the top or onto the wall a bit for a 3 dimensional mounting plate.

Here are my pictures of the bar from the A pillar to the strut tower. It really just barely fits and I had to locate the bar further away from the strut tower itself than I would have liked. The closer you get to the end of a tube the stiffer it is (you'll verify this if you get a tubing bender), so it's much better to be right next to the end than in the middle of a span, so it's still pretty good.

Posted Image
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And here are my drawings on your pictures. I also am not a paint master, so hopefully you get the idea. One thing to take note of is the straight shoulder bar. If you are over about 5'8" tall (guessing) then you might have issues with the shoulder bar interfering with the seat going all the way back. I bent the shoulder bar to allow the seat to go all the way back, and that basically means that I cannot really do the bar from the door bar to the strut tower. Those two cannot coexist built off of the same node, note Dan doesn't have one either. Alternatively you could move the shoulder bar up or down or move the door bars up or down. Ideally you would want the diag to meet the hoop supports, but again, if you're tall you can't have that in a Z because it prevents the seat from moving as well, so that frees up the main hoop support location. I put my rear supports just under the bend in the main hoop, and then put a plate on top of the strut tower trapezoid and welded the support to that. If you decide to ditch the door bar to rear strut tower bar, then you can do this too, and the support would then basically serve the same function in a T bone accident. Might be higher than one would like though.

The one thing I didn't include from my own cage is the X from the rear strut towers to the bottom of the main hoop. It was a real pain in the ass to weld in, so unless you're hyper-anal like me, I'd suggest skipping it. If you do add that, cut the stupid shelf out first instead of trying to leave it in the car.

I'd be curious to see what some of the other guys have to say as well.

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Jon Mortensen, owner/operator www.petdoorstore.com


#18 redneck1545

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Posted 28 August 2011 - 03:10 PM

Ok so I got off my butt today and tried to finish the backhalf of the cage. Below are some pictures of what I came up with. Some of the notches didn't come out perfect so I'm going to include them to see if the experts approve or if I should re-work them and make a tighter fit. I dont know if I'm being too much of a perfectionist on these things. I did the welding on most everything else on the car but I will not be the one doing the welding of the joints because quite frankly this is my first time welding and I dont trust my welds for stuff that could save my life just yet, and I have some front camber plates that I need welded in so I'm leaving it to the professionals which just so happen to be a friend of the family who's been welding all his life and has been bugging me to let him help me with this car! :D

I think my boxes on my main hoop are too freakin wide though, I put my seat in the other day to check to see how far I could move it back and the first thing it hit when moving it all the way aft was the box for the main hoop. Im gonna put the car together anyways and see if its something I can live with (I'm 6'1") before I cut into my boxes and make them skinnier. SCCA permits they cant be any shorter then 4" on any one side I believe and I haven't measured to see if that will allow the seat to move a few more inches aft or not.

The strut tower plating is .100" thick plate. SCCA mandates a minimum of .080" and I'm hoping to keep this car sub 2400 lbs...we'll see how well that works out later on haha.

Anyways here's the pictures of the stuff I did today. All these bars are made from 1.5" .095 wall DOM tubing.
The first picture shows the main hoop location in relation to the roof line. I actually took some 1/8" angle and fit in between the headliner brace and the main hoop and used ratchet strap to make sure it stayed in place. It should leave me about 1/8" clearance between the dome light brace and the main hoop. Hopefully it wont rattle going down the freeway.
Attached File  roll cage dome location.jpg   81.59KB   127 downloadsAttached File  roll cage flat.jpg   130.78KB   158 downloadsAttached File  roll cage left main.jpg   80.81KB   162 downloadsAttached File  roll cage main left.jpg   75.32KB   159 downloadsAttached File  roll cage main right.jpg   82.82KB   160 downloadsAttached File  roll cage new.jpg   135.49KB   149 downloadsAttached File  roll cage new mount.jpg   113.47KB   170 downloads

I decided on making some adjustments to my cage after looking at some other cages vs Dan's cage. It just seems the better place to spread load and keep the chassis stiff is to plate the top of the strut tower and add attachments to the plate so thats what I did.

The main hoop and diagonal bar from top to bottom will have a gusset welded in place later on. Could I do 16ga gussets? or should I stick with .100 plate? The main hoop will also have a shear gusset added to the wheelwell as well.


And now the notches...
Let me know what you think.
Keep in mind these pics were taken really really close up so It might be hard to "scale" how big or small these gaps are.

Attached File  notch1.jpg   91.93KB   178 downloadsAttached File  notch2.jpg   107.15KB   158 downloadsAttached File  notch3.jpg   118.27KB   151 downloadsAttached File  notch4.jpg   105.93KB   161 downloadsAttached File  notch5.jpg   73.75KB   170 downloadsAttached File  notch6.jpg   86.6KB   137 downloads

Edited by redneck1545, 28 August 2011 - 03:24 PM.


#19 JMortensen

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Posted 28 August 2011 - 04:01 PM

I would fix the last three notches. I didn't even consider putting the door bar brace to the rear stays. That looks like it will work nicely.

You can do a gusset or two to the map light bar. I would suggest doing that regardless of whether you thought it would rattle. 1/8" is pretty dang close.

Might also be able to cut the front inner corner off the main hoop boxes and put a plate in the resulting rectangular hole rather than cutting the whole thing lengthwise to refit.

It looks like you know this already, but clean the tubes before welding. Looks really nice so far! :2thumbs:

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#20 proxlamus©

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Posted 29 August 2011 - 06:51 PM

Love this thread!

Lots of good info and pictures for those of us who are big visual guys
Currently on a rotisserie for a full restoration - L28 with 9mm rods, 88mm Ross pistons (3.0L), 8.5:1 CR, Schneider Stage II cam, Holset HY35W, Megasquirt, Suzuki GSXR ITB's and home made intake plenum, Z32 transmission, Fidanza aluminum flywheel, ACT stage II clutch and pressure plate, coil-overs, vented 4x4 front brakes, 240sx rear brakes, Corbeau FX1 Pro seat, (soon to be half cage) and still debating the paint.. hurm




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