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Ham Sammich

Roll cage engineering, Plynth boxes and the main hoop.

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 I think the information exchange alone has been but a small piece of gold, and given me a few ideas on how I can make things better for my car. 

 

Exactly. :)

 

I've already come away with a few new ideas.  Good stuff!  :)

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I disagree - but, then again, we can both disagree with each other, and that is our perogative.... ^_^  

 

We certainly can, but your extreme over building practices are possibly adding so much weight to your car that it is keeping you from the podium, a problem that we do not have ;)

 

I can guarantee you that if you look in any pro car, from NASCAR to TransAm to SCCA or NASA, you will not find a single one of them with 3/8" plates under the mounting feet of any part of the roll cage. It is wasted weight that does nothing structurally if the cage is designed properly. 

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We certainly can, but your extreme over building practices are possibly adding so much weight to your car that it is keeping you from the podium, a problem that we do not have ;)

 

I can guarantee you that if you look in any pro car, from NASCAR to TransAm to SCCA or NASA, you will not find a single one of them with 3/8" plates under the mounting feet of any part of the roll cage. It is wasted weight that does nothing structurally if the cage is designed properly. 

 

Well, now you did it..... I'm gonna have to go dig out my "_ _ _ _ _  To Win" books and see what Carroll has to say on the subject.  ;) 

 

Dammit man - interrupting my precious beer and tequila drinking time with all this nonsense!!  :P

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It was mentioned earlier about X-bars and the reason they're used in Rally Cars, etc,.etc.  I would ask those that either have chosen, (or considering), a cage type........... to go on to YouTube and do a search on Georg Plas.  Georg was one of the better hillclimb competitors in Europe, who took a Judd V-8 engine and mated it to a BMW 3-series 'what ever you want to call it'.  (Those are my words BTW).  OMG, the sound of it was just beautiful. 

 

Anyway, there is a few videos up of his fatal crash where he missed the apex of a right hand turn and went straight off into what amounted to ROCK.  If you are quesy about watching this kind of thing,........then don't.  I look briefly and have yet to discover the real cause of the accident.  After seeing the video, I tend to think a complete brake failure was the culprit.

http://www.liveleak.com/view?i=020_1346048929

 

No gore, just one *&^%$#!ing huge impact.

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We certainly can, but your extreme over building practices are possibly adding so much weight to your car that it is keeping you from the podium, a problem that we do not have ;)

 

I can guarantee you that if you look in any pro car, from NASCAR to TransAm to SCCA or NASA, you will not find a single one of them with 3/8" plates under the mounting feet of any part of the roll cage. It is wasted weight that does nothing structurally if the cage is designed properly. 

 

to be fair, none of the big dogs are welding a cage to a thin sheetmetal floor... they are welding it to a chassis made out of some flavor of square tubing.. which is less than 3/8" thick...

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This is an RX7 where the customer brought me a roll bar kit for their drag car. I had to use a plynth box here, but you can still see where I caught some extra vertical surface to weld to:

10553419_978897688802719_259006580579099

 

 

This is the cage in our Lexus, before it went back in for the final time. There is a vertical bar dropped from the center of the X, and another mostly vertical bar that runs from the base of the A pillar bar straight to where the top of the windshield bar mates to the a-pillar bar.

1654445_849035391788950_1386232258_n.jpg

 

 

The plate underneath the box is overkill

 

the easiest way to improve the door X's would be to overlap the tubing instead of cutting and joining. In other words, no cuts or joints at the center junction, just welded side by side.  If you look at the cross section here it's a big weak point being only 1 tube right at the center. Of course you can add a gusset but why not just leave it stronger and easier in the first place.

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Also, I'm starting to be of the opinion that welding the complete edge of the plate on the floor does nothing but weaken the floor.  If a cage can effectively be held in with a few bolts... I get the feeling a 1" stitch weld every 2" would be just fine.  and be harder to punch the floor plate through.  I also, slightly round the bottom edge of my floor plates, so they aren't a sharp 90 degree edge.  In sections where they are not welded, I feel it makes it that much harder to punch through.

 

opinions on any of that?

 

The only problem with going all the way to the floor is you can't get the cage as close to the roof as you can with a box. So less headroom for taller drivers in small cars. (Unless you do like Cageruss and cut a hole in the sheet metal)

 

I think you are going overkill here. We are talking compression of the tube. Look at the cross sectional area of a piece of 1.5" x .095" tubing. All the force is going through that. Then you are going to a .125" plate that you are trying to punch through. Add the area of the weld bead also. Then you are spreading that force over 25 sq. in. of sheet metal. With .040" sheetmetal that's about 2 times the cross section area of the tube cross section.

 

With a 25 sq in plate the weak point is the cross section of the tubing. Everything else you've added to this basic setup is overkill and unnecessary weight.

 

The easiest quickest and lightest way to add, if you want to add, would be some simple triangle gussets.

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It was mentioned earlier about X-bars and the reason they're used in Rally Cars, etc,.etc.  I would ask those that either have chosen, (or considering), a cage type........... to go on to YouTube and do a search on Georg Plas.  Georg was one of the better hillclimb competitors in Europe, who took a Judd V-8 engine and mated it to a BMW 3-series 'what ever you want to call it'.  (Those are my words BTW).  OMG, the sound of it was just beautiful. 

 

Anyway, there is a few videos up of his fatal crash where he missed the apex of a right hand turn and went straight off into what amounted to ROCK.  If you are quesy about watching this kind of thing,........then don't.  I look briefly and have yet to discover the real cause of the accident.  After seeing the video, I tend to think a complete brake failure was the culprit. 

 

The fact remains that neither an X-brace or NASCAR BARS would have saved him.  What's important I think, is the bracing to the wheel well floor from the A pillar bar.  I've been thinking to add a couple of short pieces from the dash bar to the firewall in order to help support it in a straight in crash.  Georg's front OE firewall had been modified a great deal and a good portion of it replaced by just flat sheet metal. 

 

I'm not about to enter into a discussion to try to change someone's opinion or way of thinking on door bars.  We're adults, and we possess the God given ability of free will.  However, I am encouraged by the exchange of ideas and thoughtfulness put forward.  I think the information exchange alone has been but a small piece of gold, and given me a few ideas on how I can make things better for my car. 

 with engine swaps a lot of the OE stuff can get cut out. And he probably didn't have an OE front bumper which is part of the crash worthiness of the front of a stock vehicle.

 

If you cut a bunch of the front out you need to extend the cage.

 

It looks like he lost his steering. He just goes straight off the turn. Highly likely the steering was modded to go around the V8 exhaust.

 

edit, just looked at some pics of the chassis. It's a full on tube frame race car. Don't know how much you can protect though going head on into a rock wall.

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To be sure, a cage to deal with the rock wall would be pretty impossible.  Although, it does suggest that anyone doing an engine swap might need to consider the implications of either moving or putting in a new firewall.  I can think of one SHO motor shoe-horned into a 2nd Gen RX-7 at TWS that I saw run. 


 


 


Good luck kids, it's a brave new world. 


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Chumpcars are different from this hill climb race car. Isn't there somewhere in the rules where it says you can't remove too much of the front crumple zone?


 


Everyone guts their doors but then you have the door bar part of the cage for protection. But no one commonly removes any of the front crumple zone, (except for the bumper)


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YES.

I disagree with welding holes, it seems wasted to me, the perimeter welds are doing all the work.

In principle, the longer the perimeter, the bigger area the stresses are spread over. Assuming your tube weld holds to the box or plate, a good assumption.

 

If all of your welds have perfect penetration and are though-annealed, then you're right, but that is rarely the case for home-built. Even pro-built only make $ when they keep labor hours low so they've a disincentive as well. Cup guys sometimes rush welds too, we're all human.

The only way to reduce stress is to increase area, so think of ways to do that efficiently.

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I felt instant sadness the first time I had seen this :(

Having seen the aftermath of GenAv pilots' encounters with "cumulogranitus": D'accord.

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Kevin, did you get any flack for landing the A-pillar support tube on it's own pad and not back into the base of the front down bar? I would hope not... I like how nice and "upright" it comes into support the down bar. The A-pillar rake is so severe on the Camaro I'm thinking I'll end up with the same thing.......


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Not yet. I went around and around with how we were going to to that bar, the way it ended up allows the most room for the driver while keeping that bar straight. Had we landed it on the same pad as the a-pillar bar, it would have been much closer to the driver's left leg, which we did not like. Eventually we are going to add a flat pad from the plane of the front edge of the seat, down to the dead pedal to give the driver's leg a broad spot to hit against if there were ever a hard impact on the driver side of the car. Sitting in this car "feels" very nice. Lots of cage and the driver is a good ways from it. The pedals are extended back to put the driver more inside of the sturdiest part of the cage also. You should definitely have A-pillar support bars on an F-body with their huge windshield rake.

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Not yet. I went around and around with how we were going to to that bar, the way it ended up allows the most room for the driver while keeping that bar straight. Had we landed it on the same pad as the a-pillar bar, it would have been much closer to the driver's left leg, which we did not like. Eventually we are going to add a flat pad from the plane of the front edge of the seat, down to the dead pedal to give the driver's leg a broad spot to hit against if there were ever a hard impact on the driver side of the car. Sitting in this car "feels" very nice. Lots of cage and the driver is a good ways from it. The pedals are extended back to put the driver more inside of the sturdiest part of the cage also. You should definitely have A-pillar support bars on an F-body with their huge windshield rake.

 

Lol funny you mention pedals - after playing with seat positioning, it looks like I am moving pedals too. With a helmet on and in position to reach the pedals in the stock location, the drivers head is way too close to where the A-pillar & halo bar area come together. Fortunately GM did a nice job and has the pedals welded together as a single unit so shifting them back towards the driver should be relatively easy. Easier than relocating all of our drivers heads. Depending on who you talk to, some of our heads have already been relocated :lol: :lol: :lol:

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Not yet. I went around and around with how we were going to to that bar, the way it ended up allows the most room for the driver while keeping that bar straight. Had we landed it on the same pad as the a-pillar bar, it would have been much closer to the driver's left leg, which we did not like. Eventually we are going to add a flat pad from the plane of the front edge of the seat, down to the dead pedal to give the driver's leg a broad spot to hit against if there were ever a hard impact on the driver side of the car. Sitting in this car "feels" very nice. Lots of cage and the driver is a good ways from it. The pedals are extended back to put the driver more inside of the sturdiest part of the cage also. You should definitely have A-pillar support bars on an F-body with their huge windshield rake.

Nice cage.

 

They didn't ding you for having more than 8 mounting points?

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