stony Posted May 31, 2002 Share Posted May 31, 2002 minus the bars that go thru the passenger area this is the cage i want to build this is the part i like Quote Link to comment Share on other sites More sharing options...
Ray Posted May 31, 2002 Share Posted May 31, 2002 Nice....do you have any pix of what the front bars going through the firewall do... and how about some closeups of the attaching points for the front down tubes.. Looks alot like a dirt track cage minus the doorbars.. the x on the passengers side seat and the knee knocker bar are a little much for the street.. I do like the how they went down from the x in the door to the rocker.. I have mine almost completely in but am looking at tieing the the rocker, front down tubes and the lower front frame rail together. I am thinking about running half a peice of 2x2 .083 box from the rocker to the frame rail... have you seen anything like that???? Quote Link to comment Share on other sites More sharing options...
johnc Posted May 31, 2002 Share Posted May 31, 2002 Unfortunately, the bars going through the passenger area are critical. If you are going to eliminate those bars you need to design a competely different roll cage. Quote Link to comment Share on other sites More sharing options...
Guest Zpeed Posted May 31, 2002 Share Posted May 31, 2002 mmmm agreed with JohnC, that car looks like it won't flex with any amount of HP, or how many times u roll it and its to much for the street... its already a 2 seater car, don't want it a 1 seater car... IMO Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted May 31, 2002 Share Posted May 31, 2002 If you like elaborate cages, you may want to get the book "how to hotrod and race your datsun". The have beaucoup pictures of either Bob Sharp racing or the BRE race car cages. Very detailed, very elaborate. The car was a very successful racer so don't know how you could do better. If I remeber right it did not have as many cross pieces in the back. Quote Link to comment Share on other sites More sharing options...
katman Posted May 31, 2002 Share Posted May 31, 2002 Great in roll. Not so great in a T-bone. Also a lot of weight up high that's not really contributing very much. It can be done better, safer, lighter. Gone racing for a week, when I get back I can see I'm gonna hafta elaborate. This roll cage subject just isn't going to go away. Quote Link to comment Share on other sites More sharing options...
stony Posted June 1, 2002 Author Share Posted June 1, 2002 i was more interested in the stuff behind the seat which looks to me like it would eliminate any type of chassis flex. the bars in the passenger area and shin knockers are out of teh question. I dont plan on this exact cage but something like that will tie the rear strut towers and the main hoop together along with everything else. the x bars will be more like a Y. I dont want to make it too hard to get into and out of the car. heres the site for the car Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted June 1, 2002 Share Posted June 1, 2002 Katman I have read several of your previous posts concerning cages. They seem really well informed. I for one would value you summarizing your ideas on what makes a good cage (for both street and race). Or better yet, show us pictures! I want to stiffen my street Z to better handle V8 torque but I don't really want to go all out Dukes of Hazard with it. Any pointers? Also I have often wondered what has to be done to the stock dash when a cage is run through it. Anyone have any pictures? Or is it time to break out the aluminum sheet and build a new dash? Thanks in advance Quote Link to comment Share on other sites More sharing options...
johnc Posted June 1, 2002 Share Posted June 1, 2002 Keith, Maybe not as much weight up high if they were smart with their tubing selection. The horizontal X over the passenger area seems excessive, unless they are doing something special in the center of the engine compartment. I'ma ssuming this is an EP car. Quote Link to comment Share on other sites More sharing options...
katman Posted June 2, 2002 Share Posted June 2, 2002 Yeah John, you're right. X over the pass compartment is what I was thinking when I said they got some tubes up high that aren't really doing much. The basic problem with this cage is the X for the door bars, and the high tube up front in the dash area. Here's why. In a T-bone with this cage, the X is going to try to send load equally to the floor and to the upper region of the cage. Unfortunately, the load really wants to go low, because low is the loadpath to the engine and rear diff/suspension, and the load wants to go there because F=MA, where F is the other car hitting you, and M is the mass of this car being accelerated (the "A"). Most of the mass is where? Engine up front, diff/suspension/gas tank in rear. So only half the tubes in the X are involved with reacting the impact to where it wants to go. I always put 2 NASCAR type door bars in, sorta horizontal, where the upper one intersects a LOW bar1/2 inch above the tranny tunnel under the dash. This helps keep the left front downtube ("A" pillar tube) from folding inward toward your left leg, and helps to involve the entire floorpan and firewall sooner in the impact sequence. If its an EP car, and I think John is probably right on that too, it would be legal to arch the door bars out into a gutted door, which I always do if the class allows. No sense in not trying to keep the impact as far away from body parts as possible (even though as a crew chief I generally would prefer a robot over a driver, but SCCA still frowns on that and a good shoe occasionally will bring sponsor money...). That's just an example of how this cage could be better. I would like to see what happens on the other side of the firewall. Looks like it will be a really nice car though. Wonder why he didn't mount the fuel tank to the far right, 2 inches lower, and offset the driver seat to the right an inch or two? Hmmm, may be racing somewhere other than on US road courses... Quote Link to comment Share on other sites More sharing options...
katman Posted June 2, 2002 Share Posted June 2, 2002 Originally posted by Jim Powers:Katman I have read several of your previous posts concerning cages. They seem really well informed. I for one would value you summarizing your ideas on what makes a good cage (for both street and race). Or better yet, show us pictures! I want to stiffen my street Z to better handle V8 torque but I don't really want to go all out Dukes of Hazard with it. Any pointers? Also I have often wondered what has to be done to the stock dash when a cage is run through it. Anyone have any pictures? Or is it time to break out the aluminum sheet and build a new dash? Thanks in advance A good primer on cage design is that old Z-Car Mag article on building a cage for an ITS 240Z (that Jefferson Spiedel guy was a genius). When I get back next week I'll find a way to get it posted somewhere, along with some extra pictures that will show how we do the stock dash. Sorry you'll have to wait. As far as stiffening the chassis for V8's, I need to think about that some more, but I will, I got the same problem staring me in the face every time I have to shoo my wife's cats off my project. I do know the weak link is forward of the firewall, and the most efficient way to help that is with a strut bar that triangulates back to the top of the firewall. That helps the overall front end torsion flexibility a lot, but there's also probably something we can do on the bottom. I've seen some ideas for that on this forum, but haven't really thought about it enough for a street car to comment yet. For dedicated race cars we can take liberties that don't translate well to something you have to live with every day. I'll get back with you on that. Quote Link to comment Share on other sites More sharing options...
ZROSSA Posted June 2, 2002 Share Posted June 2, 2002 I still really like the idea of a backbone chassis for a road car. Kind of a mini space frame that runs along the trans tunnel. This would pick up the rear struts behind the seats and go through to the fire wall and meet the top of the front struts and the compression struts at the bottom. It would be welded to the trans tunnel at as many place as possable and then i might rivit flat ali. sheet to it for x- bracing. Like a lotus 7. This still wouldnt help in a side impact though. I like the idea of the door bars that katman talks about but I dont like the extra weight. I dont belive that they ad much to chassis stiffness, only saftey. If you look at cages where weight is at a premium they dont have door bars. Cheers Douglas Quote Link to comment Share on other sites More sharing options...
Michael Posted June 11, 2002 Share Posted June 11, 2002 I have a roll cage somewhat similar to the one featured in this thread, so I thought I’d comment on some issues…. The X-bars in the car featured above actually tie into the unibody at all four corners of the "X"; I refer in particular to (1) the areas just above and aft of the upper hinges of the doors, and (2) the “corners” of the unibody where a B-pillar would normally be (the latter are tied together by the horizontal bar behind the seats). The continuation of the tubes forward of the firewall is unclear, but they look like "Monte Carlo" bars triangulating the front strut towers. With that in mind, I'd say that in fact the upper half of the roll cage IS doing it's fair share of reacting to the loads of a side-impact. It's true that in a harsh T-bone, the X-bars will deflect into the driver's shoulder/thigh area - and in that sense they are inferior to NASCAR-style straight door bars. But they weigh less and do a better job of stiffening the whole chassis in torsion. So we might conclude that for safety purposes they are not the best design, but for stiffening the car they perform fine. It comes down to a matter of what's the main reason for building the roll cage: safety or stiffness? From what I have heard, a NASCAR-style cage is astonishingly weak in torsion – so much so, that frame deflection is taken into account when computing the suspension dynamics. Regarding the diagonal bars occupying the passenger compartment - my suggestion is to replace them with a single bar running from the midpoint of the dash bar (a node of several intersecting tubes) aft toward the midpoint of the horizontal bar just behind the seats (another node). That is, connect node-to-node. This ties together the rear strut tower triangulations and the front strut tower triangulations (which is what the horizontal-plane X-bar set was evidently designed to do as well), improving the torsional and bending stiffness of the whole car. I have such an arrangement in my car. It looks like an awkward invasion of interior space, but actually it does not interfere with the driver’s movements. Quote Link to comment Share on other sites More sharing options...
katman Posted June 11, 2002 Share Posted June 11, 2002 Bingo! The X type door bars do a more efficient job of helping with overall shell torsion, the real weak link in an old Z. Well stated. In my cages I actually angle the upper door bar so it gets me some additional truss action for just that reason, plus it follows the squishable parts of a driver better. Attaching the cage at the ends of the X's to the unibody is a must do like you say, when the rules allow it. Quote Link to comment Share on other sites More sharing options...
katman Posted June 11, 2002 Share Posted June 11, 2002 Originally posted by Michael: From what I have heard, a NASCAR-style cage is astonishingly weak in torsion – so much so, that frame deflection is taken into account when computing the suspension dynamics. I don't doubt that the more sophisticated teams include chassis stiffness (all degrees of freedom) in their suspension dynamics models, but I find it hard to believe they are astonishingly weak in torsion. At least not because of their door bar execution anyway... Quote Link to comment Share on other sites More sharing options...
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