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EF Ian

Cages - Experiences wanted

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I am considering getting a half cage made for the 260Z. Mainly to stiffen up the shell, provide an attachment point for the odd time I would want a harness and also to add some safety in the event of an accident. 
 
 
 
Has anyone here got experience running a cage?
 
Do you see a noticeable difference in chassis rigidity?
Problems with insurance?
I imagine a decent half cage would add at least 30kg which is not so desirable.
 
 
 
 
I am thinking something along the lines of these (only without the front half on those that are full cages)
 
 
 
DSC_0159_Large.jpg
 
 
 
Datsun_S30_240Z_280Z_Comparo-32.jpg
 
 
 
post-16956-0-46657600-1422237072.jpg
 
 
 
20-6.jpg
 
 
 
027.jpg
 
 
 
026.jpg
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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I have a full weld in cage in my 280zx race car. Its the only thing keeping it togheter. The cage really stiffens up the car, specially the rear since its attached to the rear strut towers. 

 

Is there any thing in particular you are curious about? 

 

Cost is between $1000-$4000 depending om what you want.

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Well, I guess the main reason most people fit a cage is for safety however I'm mainly wanting it to increase the strength of the chassis so I was hoping to get some responses as to how much difference those running a cage felt it made to the rigidity of the chassis. Response so far from anywhere I've asked is very positive that they notice a big increase in how stiff their chassis feels. This is what I was hoping for as to add a half cage will mean adding nearly 30kg of weight and given how hard I've tried to save weight in my Z I had to know that this extra weight would be worthwhile.

 

At least with the weight I've saved recently the overall gain won't be massive as I've saved over 10kg with carbon bonnet, over 4kg with fibreglass wings, a couple of kg with alloy hubs so it might only end up 10kg heavier than previously. Considering going to a fibreglass front bumper and getting that chromed, will look original but should save me a fair amount of weight. Just that its expensive as I was Quoted over 700 to chrome it, and that is Pounds sterling, not dollars.

 

 

 

 

 

 

Cost I'm not so concerned about as I've allowed up to £1000 for the work, I think this should see it done.

 

I'm going to be going with a design similar to this.

 

Datsun_S30_240Z_280Z_Comparo-32.jpg

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So is a half cage just the rear? Why not a full cage, weight and cost?

I like to look at real professional race cars for inspiration.

 

You could also add add bars from strut towers to firewall as well or get a nice 4pt strut bar.

I got one from RaceTep, but that think broke...snapped. 

 

 This is from a 280zx: 

 

Ex-Jim Fitzgerald 1979 Datsun 280ZX Racer

 

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2 hours ago, turbogrill said:

So is a half cage just the rear? Why not a full cage, weight and cost?

Not cost, but weight and primarily a road and I don't want the hassle of having a cage in the front, plus its not the look I'm going for, trying to keep the style minimal, clean and close to original, a full cage just doesn't fit with the rest of the car.

 

 

 

 

 

2 hours ago, turbogrill said:

I like to look at real professional race cars for inspiration.

If it was mainly a track car thats a really good idea.

 

 

 

2 hours ago, turbogrill said:

You could also add add bars from strut towers to firewall as well or get a nice 4pt strut bar.

Bulkhead isn't really strong enough, you need a full to do that effectively, as then you can link the bars from the strut towers up to the rest of the cage.

 

Unfortunately I can't run strut bars in the front as my engine sits too high.  

 

 

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Posted (edited)

Searching "chassis stiffening" might get some better hits. Link below.

https://www.google.com/search?q=chassis+stiffening+site%3Aforums.hybridz.org&oq=chassis+stiffening+site%3Aforums.hybridz.org&aqs=chrome..69i57.7719j0j4&sourceid=chrome&ie=UTF-8

For my $.02, if you're only doing a roll bar I would weld a shear plate from the top of the hoop to the map light bar on the chassis. Had a friend who built a really simple 4 point bar with an SCCA legal diagonal and shoulder bar on his 240. He said after he welded the plate to the map light area his rear interior plastic pieces stopped squeaking when he went in and out of driveways. Made a very noticeable difference.

On my 70 I really thought the front of the car needed a lot of attention. I could jack up the front on the xmember, set jackstands under the TC buckets, and literally see the frame rails drooping when I let the jack down, and hear it all creaking too. The chassis is pretty flexible at the firewall, apparently. If you look at the old Bob Sharp pics (which you can find here) they spent some time reinforcing the area between the door hinges and the firewall, presumably to help that issue. There are also tubes that people run from the rockers to the upper frame rails. I think these kinds of mods are worthwhile if you don't want a full cage. It's what a triangulated strut tower setup is trying to do, but I don't think the triangulated bars are very effective unless you beef up the area of the cowl that you attach to, which almost nobody does (except bjhines).

Another one to look at is the cage that Dan, 74_5.0L_Z, did on his. It's basically how you would cage a convertible with no windshield. I really think he did a good job for a streetable car, where you don't have to worry about hitting your head on the A pillar tubes. I did a full cage and my helmet rested on the halo. Had to move the seat towards the center, will also probably have to lower the seat more or use a 20* seat, as I have a 10* in there now. 

Edited by JMortensen

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Thanks for your response and your advice/opinions, its appreciated. 

 

 

19 hours ago, JMortensen said:

On my 70 I really thought the front of the car needed a lot of attention. I could jack up the front on the xmember, set jackstands under the TC buckets, and literally see the frame rails drooping when I let the jack down, and hear it all creaking too.

Well, thankfully my car is actually quite stiff, but that doesn't mean it shouldn't be improved. Theres no visible drooping no matter where I jack it up and even jacked up my doors still open and close without issue (not like in my Civic) Theres also no creaking to speak of from the interior panels. Shes a solid girl so perhaps I'm doing work for nothing, but I can't help thinking I'll have problems eventually with running 490ftlbs and 245 semi slicks.

 

Actually one of my biggest surprises after buying the car originally was just how stiff she felt, I was expecting an old classic like her to be sloppy, but there wasn't a bit of that even with her stock. Perhaps that how she puts the power to the ground better than most S30's I've seen.

 

 

 

 

19 hours ago, JMortensen said:

spent some time reinforcing the area between the door hinges and the firewall, presumably to help that issue. There are also tubes that people run from the rockers to the upper frame rails. I think these kinds of mods are worthwhile if you don't want a full cage.

I actually have already done this, the chassis rails in the bay are strengthened and seam welded along with several other seams on the front area and I have bars going from the door hinge area to the inner upper frame rails and across the the traction rod mounting area. My front end is solid as I had it back to bare metal pre engine swap and carried all this work out then. Lucky because I can't run a strut brace as the twin turbo pipe on the RB sits too high to fit a strut brace over.

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Lots of years ago 74_5.0L_Z had a drawing in his gallery for the main hoop.  Use it, couldn’t fit better.  Put rear downstays on top of strut towers not on the front vertical surface.  I wouldn’t get fancy with X just simple diagonal in main hoop and as Jon says plus tie into the roof and B pillars.  And weld a bar across between the towers.  If you are tracking you want at least a hoop.  The roof may be relatively stiff but folds easily on impact.  Ask me how I know ....

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On ‎3‎/‎18‎/‎2018 at 7:56 AM, EF Ian said:
I am considering getting a half cage made for the 260Z. Mainly to stiffen up the shell, provide an attachment point for the odd time I would want a harness and also to add some safety in the event of an accident. 
 
 
 
Has anyone here got experience running a cage?
 
Do you see a noticeable difference in chassis rigidity?
Problems with insurance?
I imagine a decent half cage would add at least 30kg which is not so desirable.
 
 
For a street car I would recommend not to put a cage as I have one Z with a 9 point cage but I also have two Z's that have boxed frame rails that go from the back all the way to the front of the car.  That has made the car even stiffer than the car with the cage and I was in one of the frame railed cars stopped on a highway when a Prius rear ended me at 50 mph and the car had no frame damage as once the impact hit the rear start of the frame rail it did not bend any of the frame rails.  That saved my life and provided the rigidity for racing on the street with no bars in the way for daily driving; I have a 5 point harness with a fully adjustable Konig racing seat.

 

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And refer to this comment by John Coffey if you haven't already seen it pop up. Some people get a little crazier with cages, but in the same thread this is from John recommended (more accurately, he stated): "Never run a full roll cage on a street car" 

 

For a street driven S30, here's about as much as you can do to stiffen the chassis:

 

1. Seam Weld (every sheet metal seam overlap.)

2. Bad Dog Subframe Connectors

3. Weld-In Roll Bar.

4. Welded In Rear STB.

5. Triangulated Front STB.

6. Radiator Core Support Reinforcement.

7. Transverse Link Bracing Reinforcement.

8. RT Diff Mount.

9. Tubular Seat Mounts.

10. Box Upper Frame Horns to Firewall/Cowl.

11. Reinforce Pedal Box/Brake MC Mount.

12. Reinforce Front ARB Mount.

13. Reinforce Front Strut Tower to Frame Rail Junction.

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Not sure how much stiffening it is doing unless as Jmortenson says you are welding/gusseting to the car.

 

From a use standpoint I'd seriously consider the ones that mount on the wheel well for a street Z. Unless you keep it real tight you are going to lose backwards travel in your seats if you push it down towards the floor. I've got about 3 inches or so I can't use because of my little box for the main hoop.

 

For harness mounting I think the diagonal with the harness bar might be preferable to mounting it at the rear shock tower just from an angle perspective. 

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On 27/03/2018 at 6:48 AM, heavy85 said:

Put rear downstays on top of strut towers not on the front vertical surface.

My seatbelts mount on the top so I'd rather have them just in front of the top on the vertical.

 

 

 

 

On 27/03/2018 at 6:48 AM, heavy85 said:

Lots of years ago 74_5.0L_Z had a drawing in his gallery for the main hoop.

 

On 25/03/2018 at 12:18 AM, JMortensen said:

Another one to look at is the cage that Dan, 74_5.0L_Z, did on his

Just looked it up, thanks, got some ideas from that.

 

 

 

 

On 27/03/2018 at 7:28 AM, primaz said:

For a street car I would recommend not to put a cage

Totally wouldn't want a full cage with door bars, but with the design I have in mind for my half cage I can't see it getting in the way at all.

 

My frame rails are good and I will be extending them to the rear subframe so its good to hear this proves worthwhile.

 

 

 

 

 

On 27/03/2018 at 7:02 PM, Zetsaz said:

And refer to this comment by John Coffey if you haven't already seen it pop up. Some people get a little crazier with cages, but in the same thread this is from John recommended (more accurately, he stated): "Never run a full roll cage on a street car" 

Thanks. I actually read that thread before I even bought my Z.

 

I have or will have 1, 2, 4, 7, 8, 11, 12, 13 and possibly 3 as we are discussing here.

 

 

 

 

 

23 hours ago, seattlejester said:

From a use standpoint I'd seriously consider the ones that mount on the wheel well for a street Z. Unless you keep it real tight you are going to lose backwards travel in your seats if you push it down towards the floor. I've got about 3 inches or so I can't use because of my little box for the main hoop.

With my design that I have in mind I do not believe I will loose any seat travel, at least not any of the adjustment I would need for driving.

 

 

 

23 hours ago, seattlejester said:

For harness mounting I think the diagonal with the harness bar might be preferable to mounting it at the rear shock tower just from an angle perspective. 

I may make a removable harness bar as I would only be using harness on track, drag strip or runway. 

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The pretty popular harness bar using the safari cage mount points would do the trick pretty well. 

 

Also just saw your questions for some reason I missed them the first time.

 

My bars are pretty visible given mine are painted white, my insurance agent and company didn't comment on them, they were more interested in making sure the panels were more or less in good shape.

 

I think the way a roll bar is doesn't add too much stiffness unless you weld it to the roof like JMortenson says. I have subframe connectors, welded in strut bar, and a roll bar and the hatch still doesn't want to close straight if I park off camber

 

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On 3/27/2018 at 2:38 PM, seattlejester said:

From a use standpoint I'd seriously consider the ones that mount on the wheel well for a street Z. Unless you keep it real tight you are going to lose backwards travel in your seats if you push it down towards the floor. I've got about 3 inches or so I can't use because of my little box for the main hoop.

Can you post a pic? I was planning on a 4pt roll bar for safety, stiffness, and as a place to mount harnesses, but this is giving me pause.

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1 hour ago, EF Ian said:

I may make a removable harness bar as I would only be using harness on track, drag strip or runway. 

I take it you plan to run 3pt seat belts on the street? And I believe you have a '78, with seat belt reels on both the strut tower and on the floor, yes? If so, this is going to be harder than you think. If you want the roll bar for stiffness, mounting it on the wheel well isn't gonna do anything. Going from memory so I may not have the details right, but John C had the S30 chassis analyzed (I forget the method), and apparently found that the chassis flexes at the front and rear bulkheads "like a hinge." The solution to the front is the 3pt strut tower bar, as well as the bar going from top of rocker to upper chassis rail. Solution for the rear is a 4pt roll bar, and as mentioned, gusseting the bar to the roof helps as well. I'm not 100% sure what he's calling the rear bulkhead, but I think it's like the area about where the tool boxes are.

 

So, the problem here, since you want 3pt seat belts, is that your main hoop needs to go right where your seat belt reel is. I'm planning on doing the same as you, and I think I might have a solution using a slightly modified belt from a newer BMW, but obviously haven't gotten to that point yet. Basically the reel bolts to the stock location on the strut tower, and rather than another reel, the lower belt anchor simply bolts to a location already on the car, like the 240Z seat belts do. Sounds sketchy, but I'm fairly certain it'll be safe. Custom seat belts are also an option.

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Hmm I didn't really think of the rear bulkhead area as being a flex point, but I can kind of see that now, the front is really easy to see as a hinge point, I've seen it do its thing with one side rusted out. I've seen some at junkyards folded like a bananna on the side with the battery with how they leave the cars.

 

5f8be10a.jpg

The black makes it a bit hard to see, but it is pretty tight to the rear wheel well. The stock seat has a pretty thin frame so it can move back and forwards, but with my recaro knock offs and my sparco R100 the hinge for the seat sits right up against the leg of the roll bar so I can recline it one click even though the seat could probably recline 3 or 4 clicks if the hinge wasn't blocked.

 

My point about the ones on the rear wheel well was kind of towards that though, I was thinking it won't do much so making sure it doesn't affect seat choice would be preferable. My bar is pretty bad to start with, but now I'm thinking if it can actually be made somewhat useful.

 

rturbo makes a good point regarding seat belts, the bar definitely covers up the stock mounting point. I've seen brackets that space the seat belt mount back for some cars, alternatively I guess you could weld a mount onto the roll bar? I'm not sure from a safety perspective.

 

Honestly being a bit on the larger side, being able to buckle in the middle versus down in the corner is not a downfall in my case.

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Yeah, I'm looking at your rear bars, it looks like the mount somewhere in the trunk? I'm also looking at where your main hoop mounts. It's hard to see, but it looks like it could go back a little more, is that right? I'm also thinking it could be leaned back a bit. My plan was to put it pretty tight up to the wheel wells, leaving just enough to get the thing welded, and also put vinyl on the wheel wells - maybe an inch or so out. Though, I'd also consider cutting the wheel wells, and running the bar into them. If I do a bar, I'll likely do it to SCCA rules, so I'll have to double check to make sure this is all in line with their rules. My car is going to be primarily a street car, so it's important that the roll bar doesn't get in the way of that.

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Posted (edited)
2 hours ago, seattlejester said:

My bars are pretty visible given mine are painted white, my insurance agent and company didn't comment on them, they were more interested in making sure the panels were more or less in good shape.

I am with a specialist insurance company due to the mods. I actually had to renew it the other day (nearly £800 :blink:) so I took the opportunity to check if it would be an issue, for them it was't and wouldn't cost any more since my car is already super heavily modified.

 

 

 

 

2 hours ago, seattlejester said:

I think the way a roll bar is doesn't add too much stiffness unless you weld it to the roof like JMortenson says. I have subframe connectors, welded in strut bar, and a roll bar and the hatch still doesn't want to close straight if I park off camber

I don't see it like that, you are connecting the two suspension towers, connecting the towers to the rocker panels which provide a lot of the strength for the car and also providing a fairy rigid bar connecting the two rockers together and then theres a bar coming off the top of the towers whihc must help somewhat to provide some vertical stiffness for the towers upward against upwards forces. I would consider connecting it to the roof as I can use some plate in the middle and still run the trim as I would just need to trim a section out the plastic to allow it to fit.

 

My front is as reinforced as I can make a road car so I'm no longer worried there. Honestly my front end feels solid and no creaking or any visible flex no matter where I jack it up.

 

 

 

 

Heres the cage I have in mind (just imagine all the lines are where they should be as I couldn't get it perfect in paint) I plan to have the main hoop uprights part recessed into the well. With this design I reckon I can still run my stock belts. The bars in yellow are optional if they are thought to be needed. I do realise that without a diagonal in the main hoop I am loosing strength but I don't want to sacrifice the room and its not like I am racing in any competitions plus I'm sure even without I'm still going to be much safer than with no cage.

 

Cage.jpg

 

 

1 hour ago, rturbo 930 said:

I take it you plan to run 3pt seat belts on the street? And I believe you have a '78, with seat belt reels on both the strut tower and on the floor, yes? If so, this is going to be harder than you think.

Correct in both cases. But I think the cage above will be solid and still let me run my stock belts. Of course I am not a cage designer so it could be deeply flawed. I guess modern belts mounted to a small floor reel with the upper mount mounted to the cage would work.

 

 

 

 

Other ideas for fun, tell me what you think.

 

Reinforcement%202.jpg

 

 

 

 

 

Reinforcement%201.jpg

 

 

 

 

 

With no cage what is better, x on its own, bar on its own or both like below or is both not adding much other than weight?

 

X%20Brace.jpg

Edited by EF Ian

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Yea, I make no qualms, my bar is not very good. They mount to a piece of 2x2 welded into the trunk. I should revisit it with some revisions, I've also contemplated just removing it altogether.

 

The bar is sitting on a centered  3x3 plate if I remember so it could move maybe an inch or so back I think, but it is pretty tight, I think as you mention the only way to get tighter is to cut into the rear wheel wells which I have seen, but welding in the bigger tube around it and getting the weld at the bottom would probably be quite the task. I don't think you can lean it back without shortening the height quite a bit, I don't have a map light, but I think this sits right in front of where the roof reinforcement is where the light monuts. At the height it is at, if the seat could recline I could sit under the bar with my helmet on. Any shorter and the bar would have to be leaned back even further if you didn't want to risk helmet contact.

 

I think my bars thickness is SCCA, but it has a bend on the "legs" and is a bolt in, bolt together type cage so pretty sure it doesn't meet any requirement there. Yea my car is not a very good street car and it gets driven pretty infrequently. I will admit it is kind of nice having the harnesses and the roll bar in because it makes it a bit more of an event getting in, visually it looks pretty nice, and if I rolled over I think it would keep the roof up, if I got rear ended though I feel like it would possibly just roll forward given where the rear legs mount.

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If you tie in the suspension towers than a half cage would make a difference, although at that point a triangulated strut brace like PDK or I think even now TTT sells would be pretty effective pretty much similar to the last one you have. I'm not sure there would be an additional benefit, granted I guess you could argue you are tying it to a wider leverage arm in the chassis if it flexes at the bulkhead like rturbo says.

 

I've got some heavy duty subframe connectors and I still feel like the car likes to do the twist, I guess I have never been in the car without them though, so my standard might just be really off or based off of modern unibody structures.

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I could be wrong here, but I think the idea is to sort of triangulate from the floor, to the roof, to the rear strut towers.

2 minutes ago, seattlejester said:

Yea, I make no qualms, my bar is not very good. They mount to a piece of 2x2 welded into the trunk. I should revisit it with some revisions, I've also contemplated just removing it altogether.

 

The bar is sitting on a centered  3x3 plate if I remember so it could move maybe an inch or so back I think, but it is pretty tight, I think as you mention the only way to get tighter is to cut into the rear wheel wells which I have seen, but welding in the bigger tube around it and getting the weld at the bottom would probably be quite the task. I don't think you can lean it back without shortening the height quite a bit, I don't have a map light, but I think this sits right in front of where the roof reinforcement is where the light monuts. At the height it is at, if the seat could recline I could sit under the bar with my helmet on. Any shorter and the bar would have to be leaned back even further if you didn't want to risk helmet contact.

 

I think my bars thickness is SCCA, but it has a bend on the "legs" and is a bolt in, bolt together type cage so pretty sure it doesn't meet any requirement there. Yea my car is not a very good street car and it gets driven pretty infrequently. I will admit it is kind of nice having the harnesses and the roll bar in because it makes it a bit more of an event getting in, visually it looks pretty nice, and if I rolled over I think it would keep the roof up, if I got rear ended though I feel like it would possibly just roll forward given where the rear legs mount.

Yeah, I'm by no means an expert, but I think your thoughts there are about right. Easy for to say since I don't have to pay for the replacement, but I think I'd toss it and get a proper one welded in by a good shop.

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