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I've decided to start a new thread for this build since the Fastback ZJ will be phased out.
So after much thought I have decided to build myself a tube chassis and use the ZJ as a donor rig for the buggy. This is obviously due to the GVWR on the ZJ being too low
I'm planning to build this to Ultra4 specs, in case I ever get the urge to race in one...however, it'll mostly be a trail-rig so I will build it to serve that purpose foremost.
Specs that I'm shooting for:
4-seater
114"-116" WB
42" Krawler Reds
Swap in current D60 setup
Swap in current 9" w/ new housing...or just build a 14B (which runs me into the same 6-lug/8-lug issue I had a while back)
Power train is still undetermined, thinking 6.0 though.
I'm just finishing getting the garage setup, then I'll start the work. My plan is to have the chassis done this winter, then collect needed parts next summer and swap everything next winter...
Here is the design I've come up with for it. The gray tubing is 2" .120 DOM, orange is 1.5" .120 DOM, and black is 2" .250 Square (subframe). There will be gussets in corners that need it, and some of the tubing that isn't structural may change slightly but the bare-bones of the chassis will resemble this. According to Bend-Tech, this is a total of 211' of 2" DOM, 54' of 1.5" DOM and 15' of square for the subframe. Total weight is 675 lbs.
I'm open to all comments as this is my first full tube chassis design and build and I'm sure there is some criticism that I have not yet thought of.
The lines look pretty good. I would even consider making the "boat sides" and floor crossmembers out of 1.5" square to make skids and floor panels easier to mount along with making it easier to square the thing up where it really matters. Slap some UHMW over it and no one would know you went the "easy" route and you'll have a more bending resistance down low. Plus you could have a more substantial sub frame to play with in the beginning stages of a build like this.
Different people have their own ideas when it comes to building stuff, but I would try to finalize the design around a drivetrain and suspension geometry and components rather than building a pre-defined structure and figuring out where to place things. When you go that route, you end up making the same kind of compromises you have to make building around an existing vehicle (or cutting out and redoing a lot of existing work), negating a lot of the benefit of a purpose-built vehicle. It's harder to initially visualize everything that way, but I think it's worth while.
Basically, start with known components and dimensions in order to use what you can from what you already have and maximize (theoretical) performance without having to re-build the thing three times and buy twice as many parts before it's ready to move under its own power.
Yeah, I didn't think of the square for the boat sides, that's a good idea and would definitely make mounting the UHMW easier.
I do agree that having all the parts and designing around them would be easier/better, however I don't know what I'll be using for certain (funding-wise). I did however get measurements of the seats that I'll be using for the interior, and a 6.0 for the motor with a Griffin radiator/fan combo for the front end and designed the front-end to fit that in. Suspension links and components are the next thing I'm working on to see how this will all work out in the 4-link Calc.
Sounds like you've got a pretty good plan in place. You could always do a NV241/ Ford 205 combo for a budget-friendly, fairly bomb-proof twin-stickable 4 speed that would be easy to put together behind a GM automatic and work with the HP60.
What do the ultra 4 rules say about minimum tube size vs vehicle weight? What I'm getting at is whether or not the 1.5" tubing you have in part of the design will become problematic during tech inspection - especially for the A pillar and windshield bars. Not doubting that it'll be strong enough, but just curious what the rules say about it.
Last edited by SirFuego; 09-10-2013 at 06:52 PM.
Yeah, I thought the same thing. The rule (6.2.5.2) states that
So assuming that the entire main "roll-cage" is out of 2" .120 wall, it looks like this should pass tech but I've got a PM into Wayne (ZukIzzy on Pirate) to see what he has to say about it as well as a thread on Pirate. The main reason I put the 1.5" there is just for a little better visibility, not that 2" is going to make a huge difference, so if they say it needs to be 2" I will do that.All vehicles must be equipped with a roll cage fabricated of 1020 mild steel mechanical tubing or better (higher carbon content or alloy steel). The
following minimum mild steel tubing sizes for roll cage main structure, based
on dry vehicle weight rating (DVWR) in race trim, not including occupants, are
recommended:
DVWR Under 3200 lb. - 1.5” diameter x .120” wall thickness.
DVWR 3201 lb. - 4400 lb. - 1.75” diameter x .120” wall thickness.
DVWR Over 4400 lb. - 2” diameter x .120” wall thickness.
Good point though, checking into it.
Cool. Looking forward to seeing this. What's your target width on the chassis at the A and B pillar? belly height?
Other than the longish wheelbase what's the reasoning for 42" reds instead of 39s? With LS power it's hard enough to keep parts alive even with 39s. At least for our group.
Since you are open to comments I would recommend two things.
1. 14 bolts are awesome
2. Strongly consider an auto - I'm getting tired of my cheap old manual trans that negates many of the advantages of an otherwise sophisticated modern setup. It's hard to beat the versatility of an auto behind an LS motor that uses technology already built into LS pcm's
Last edited by ATL ZJ; 09-10-2013 at 09:37 PM.
Here are the dimensions...shooting for a ~25" belly height.
As for the 42's, the longer wheelbase is pretty much the reason. I want a better break-over angle. I definitely have thought about it though, keeping my 39's would be easier and quite a bit cheaper being that I could keep the current wheels...that is, if I keep the 6 lug pattern.
I definitely plan on doing an auto...no question there.
dude. 54" wide chassis.
i thought 59 was narrow comming from a ZJ buggy but its HUGE. trust me on this one. mine is 54" and its got tones of room. i will take a few pics of the standard suspension seat in it if you want.
also, consider ditching the boat sides and just running a belly to the fram rails then have your rockers come out from there. and keep a high rocker line. the rig will look taller but its just optics. it keeps the wider stuff away from the rocks and alows you to squeez through things easier. this will be very important for something that long.
Cam's got a really good point of tire size. your going to need some seriouse axles for this weight/tiresize/HP combo.
if it were me i woudl get the wheel base down as short as you can. you can always extend your links later if you want, but shortening a wheel base is waaaay more work. there is a guy around here with 40's 4 seater and LS3. its got a 109 wheel base and he can follow even the smallest rear steering buggy's with not much more trouble. now the other guy on 42's with a 115 wheel base is like a land yatch and spends most of his tim eon a winch cable.
Kris, I definitely appreciate the input. If you could post some pics of yours at 54" that would be sweet.
Yeah, I'll have to reconsider the 42's...the 39's haven't let me down any thus far. I'll see how much I can tweak the front to shorten it up. That's really the only place I have much room to possibly work with. How long is your buggy from the firewall forward?
What Kraqa said. 59" is the width of a YJ/ TJ tub. It would be okay for a recreational rig wheeling in open areas, but I doubt you want to build something virtually the size of a 4 door JK if racing has crossed your mind. The frame rail idea is a good one, too.
Also make sure the front is narrow enough to allow for full sweep of whatever size tire you want to run at max steering angle.
Having full lock to lock steering is awesome. I was able to do this by triangulating the lowers a lot. Probably didn't need to as much as I did but for a lot of the guys their tires hit the lowers before they are near full lock. I think I'm the only one in my group that is not always doing 3 point turns around corners and the benefit of it on tight spots in the rocks is pretty nice.
Yeah, full lock-to-lock steering is a must. I currently have it setup that way on my ZJ. The only limiting factor is the ears of the axle shafts make contact at full-lock.
Kris, is your 54" inside of tub our outside of tub?
54" to the outside
Alright, I've made some adjustments to the chassis after taking some recommendations into account. Wheelbase should be ~109" now.
The grey tube being 2" .120 DOM, orange 1.5" .120 DOM, green is 1.5" .188 DOM, black is 2" .250 square.
Last edited by CrawlerReady; 09-12-2013 at 05:53 PM.
It looks a lot better overall, but I don't know if you'd have room for a fuel cell or any storage with the back scrunched up like that. Maybe try extending the distance behind the passenger compartment a few inches and squaring it up out back.
It's hard to tell by eyeball but it looks like you still have more than enough room in front of the firewall if you wanted to gain some wiggle room by shortening it up there. That would keep your wheelbase shorter, allow you to push the rear back a couple inches without sacrificing departure angle, and give a bit more of a front weight bias which helps climbing ability.
can you show your tire placement?
Yeah, out back is setup to fit the same size fuel cell that YJ's and TJ's run behind their seats. I had it squared off, but I didn't like the looks as much...some of the things I'm fighting in my head are function over form haha
As for in front of the firewall, I'm sitting at 48" in length. Not sure there's too much wiggle room there.
The green dots where the 109 goes to is setup to be the center of the wheel.
Kris, what is the length of your firewall forward?
this thread sucks
Finally got the garage setup since moving into this place. Built a work-bench and wired up some 220. This project is next on the list now. Picking up tube tomorrow.
Got the tube at $3.00/ft......now to see if I can make something out of this...
I took the ZJ out wheelin' over the weekend. Got one video haha.
http://www.youtube.com/watch?v=vK3EhIFZM6E
<span style="color: rgb(85, 85, 85); font-family: Verdana, Arial, sans-serif; background-color: rgb(250, 250, 250);">
So some of you may enjoy this....it makes sense as to why I have a lot of "bounce" in the rear, but it still seems to perform well anyway. I've always been curious where the ZJ stood in terms of the suspension geometry with all the changes that I've made to it....just measured it all up and put it into the calc tonight.
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