ZROSSA Posted January 11, 2002 Share Posted January 11, 2002 Howdy all, I am going to take the roof of my 2+2. I have talked to a few of you already on chassis strengthening but i need a little help on tube sizes. What i am planing to do is make a backbone chassis that is welded on to the trans tunnel. I would be done like a space frame and go through the fire wall so it joins with the struts up front. The back will join to the rear struts in a t shape very much like the older Lotus' the space frame will then have sheet metal welded to it to tie into the tunnel to the space frame. I understand the round tube is the strongest but i would pref to use square as it far easyier for me to fabricate. I dont mind useing round tube to do the x-bracing. What i am looking for is what size tubing should i use. I think i would like 1x2 inch for the main beams so any thing that joins should be 1 inch. What Guage tubing would be good. I would like this as thin as i can get away with. Its not subject to any rules i just want max stifness for min weight. Cheers Douglas Quote Link to comment Share on other sites More sharing options...
260DET Posted January 11, 2002 Share Posted January 11, 2002 I used 25 x 50mm under the sills, on end, tied into the front tension rod mounts to stiffen the body on my coupe. But if you are chopping the top you would need much more than that, specially on a +2. Did see an article once on a 'chassis' kit for a convertible conversion, can't remember where. If the reinforcing is going underneath keep ground clearance in mind. Other than that, it will need to be pretty substantial and well tied in to front/rear structural members. Good luck. Quote Link to comment Share on other sites More sharing options...
johnc Posted January 11, 2002 Share Posted January 11, 2002 The backbone you are designing will help with longitudinal stiffness on the Z (and it needs help there) but it will do little for lateral and nothing for torsional stiffness. If, in addition to your top of the trans tunnel backbone, you can box the bottom of the trans tunnel then you will create a large tube that can better resist torsional bending. Quote Link to comment Share on other sites More sharing options...
johnc Posted January 11, 2002 Share Posted January 11, 2002 The chassis will be laterally stiff at the front strut, firewall, and rear struts, but the area between the firewall and the rear struts could use some help (but, remember, we are talking about taking the chassis to unheard of levels of stiffness for a 240.) I've seen people run a small tube inside the rocker panel and connect it to a rear roll bar and the front firewall. I suggest 1" diameter with ~.080 wall CroMo tubing. You're not building a roll cage so you don't need the strength of .095 or .120 wall tubing. BTW... I wouldn't use the Viper as an example of a stiff chassis. Production based racing Vipers add a huge plate underneath that completely boxes the trans tunnel from the bellhousing to the diff. They also add a diagonal brace across the front just behind the radiator, two diagonal braces in the rear, a 6 point cage, an X brace over the engine, and lots of little gussets on the existing square tube frame. Quote Link to comment Share on other sites More sharing options...
ZROSSA Posted January 12, 2002 Author Share Posted January 12, 2002 Thanks John. I have searched but havent found any photos of the viper chassis. I had an idea that they were not that stiff buy the cages you see in the le mans ones. Buy the way you said that it will be taking the chassis past the norm for a 240 i take it if done properly it will still be way better then stock with a roof? The weak point as you say will be between the firewall and the rear but it will be wellcross braced to limit this as much as possable. Cheers Douglas Quote Link to comment Share on other sites More sharing options...
ZROSSA Posted January 12, 2002 Author Share Posted January 12, 2002 Thanks John, There will be 3 removable x members underneath to box the trans tunnel to help with torsional stiffness. I thought lateral stifness would be taken care of buy tying into the fire wall and front and rear struts? This would have stressed panels covering it so it shouldnt realy move at all. Lotus have used something similar in there road cars from the 1st elan to the esprit. I believe the viper still uses a back bone as does tvr. I realise that there are beter ways to make a chassis stronger but i think that this could work beter then subframe conecters becuase it can tie in all the suspension mounts as well. Obviously a bit more work though. Any Ideas on tube sizes? Cheers Douglas Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted January 12, 2002 Share Posted January 12, 2002 What about TVR's backbone? Has anyone been able to find any diagrams or pictures of it? Quote Link to comment Share on other sites More sharing options...
ZROSSA Posted January 12, 2002 Author Share Posted January 12, 2002 Yo, http://www.gspovey.demon.co.uk/garage/tvr/gallery/bh98f1.htm This is the best one i have found yet. These cars are very light and fast. I am not however going to but that chassis in the z. Just use the concept. Cheers Douglas Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted January 13, 2002 Share Posted January 13, 2002 Thanks for the link dude, this is a really cool link too, I urge everybody to check it out. http://www.pistonheads.com/tvr/cerbera/virtual.htm pistonsheads.com is an awesome site, I've spent the past few hours browsing through it... Quote Link to comment Share on other sites More sharing options...
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