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Joel's multipurpose XJ build (rocks/boulevard)

Tace... I think yours was one of the builds I stumbled across in my digging as your description is very similar to a few pictures I saw. I think I've searched every variaion of "low profile", "exhaust routing", "belly pan", and "tummy tuck" I could think of.

I've been reading a great deal in an effort to keep the basic questions to a minimum.
 
Pardon me, you probably knew most of the above. Hopefully the information helps someone. Now that you mention it, I've heard the no welding rule about 7075. Always wondered how they make mtn bike frames from the stuff. I work in the theme park industry which is about as general an engineering role as you can find (but we certainly know how to analyze fatigue!)
no worries, it is great info, thanks for posting it for everyone.
bike frames dont use 7075, they usually use 7005, which is weldable. similar in strength as well.
 
Hmmm, likely my mistake then. I'm not a materials engineer, but I try to at least make informed decisions for what I use where. If anyone wants a basic materials overview applicable to the automotive world I highly recommend:

"Engineer to Win" by Carroll Smith
http://www.carrollsmith.com/books/ngner2win.html

Actually his whole series of "... to win" books are brilliant, particularly if you care about the implications of go-fast projects.

EDIT:
I was curious so I looked it up and they do make 7075 frames (glad I wasn't entirely delusional), but they tend to be glued/bonded construction. Mystery solved.
 
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my jeep runs fine, and 10-12mpg on 31's is average. i dont believe anyone who claims higher than the epa ratings, which are typically pretty liberal as it is.

Yup. You're the norm here and anyone who claims to be getting less than 20 mpg is the exception. You solved it.



I getcha....sarcasm.....I didn't believe it either when I first got the jeep, but it has proven real time and time again. The trip to my hunting property and back is 198 miles. I have made this trip now over 10 times since I got the 96, and each time, it takes 9-10 gals to fill it back up, depending on how much I drive around on the property. In the 88, I have made the same trip over 100 times, and it takes ~ 15 gals to fill it back up (it varies as I never just drive out and back in it).

Don't believe me, come on out, we'll go for a drive and I will prove it to ya. I do consider myself lucky in that it does get as good a mpg as it does.

I wasn't trying to say everyone gets that kind of mileage (or even should, as I see how most people drive), but that to get as low as the OP was getting, he might have some problems to find. I know my 88 was in the 12-13 mpg range when I found out my TC wasn't locking up. Put in a switch, and got my mpg back.
 
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Hey TRCM,

Any chance you have a write-up on the converter switch? How did you prove it wasn't locking up? This sounds like yet one more thing for me to learn about, but you might save me some searching if you have the info handy. To be honest, this is the first automatic vehicle I've ever purchased. I just bought a new Mazda5 to be the family hauler and I got it with a 6 speed (only van in the USA currently sold that comes with a manual).

My wife prefers the stick as well :thumbup: but 90% of the guys playing in rocks swear by the auto.
 
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I figured it out cuz my rpm @ 60 was 2000-2100, and it should have been around 1650-1700.

IM me your email addy, and I will send you the link I used. I can't post it here, as it is on a sight that has caused problems due to copyright info I think.
 
I recently changed my exhaust out and wanted to do a backpressure test before and after to see what the effect was but ran out of time. I couldn't believe that the smashed section of 2" tube was needed. There should be adequate back pressure from the exhaust by the time it makes all the turns to get out the back and has to travel thru a cat and muffler.

I cut off the 2" section of the front pipe and tig welded mandrel 2 1/2" up to the header. The back half of the pipe was still in great shape so I reused it. To finish it I added a cat, Magnaflow muffler and mandrel tailpipe from performance curve. It turned out very nice and runs great.

(I had some pics on here but I didn't want to clog up your thread, let me know if you want something to look at)
 
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Hey Troy,

I don't mind a little clutter, I did come in here asking for advice and commentary and that inherently means this thread will wander a bit. How about a good teaser pic of your exhaust build and a link to the remainder?

-Joel
 
Exhaust (in with the new):

When I went looking for exhausts I discovered there a lot of ways I don’t yet belong in the Jeep world. There’s a lot of nice work out there but it seems like among the hardcore wheelers exhausts are treated as sacrificial and some of the jerry rigging I ran across blows my mind. I found several old threads where folks were talking about how plumber’s tape was more than sufficient to serve as a hanger cause it wasn’t going to matter long anyways. I’m just not wired to think that way. Give me a couple years on the trails and we’ll see my opinion changes.

In the meantime, I built my exhaust using piecewise using all 2.5” mandrel-bent 304L stainless. It was a good excuse to buy a band saw as well which suddenly I seem to use on everything.
http://www.amazon.com/Jet-414458-HVBS-56M-Horizontal-Vertical/dp/B00004T9KU/ref=sr_1_2?ie=UTF8&qid=1333058072&sr=8-2
The band saw came in a 125 lb box via freight and a scheduled delivery time yet had FREE super saver shipping (yeah Amazon!). I picked up a couple bi-metal blades in various tooth pitches and some stick cutting lube and I’ve been impressed with what it’ll get through

I then set out with the intent to route and/or armor my exhaust such that it’ll never get screwed up in the first place. I’m hoping it outlasts the vehicle.

Cat: Mangnaflow 45036 (the California legal version costs more for no apparent reason)
http://www.magnaflow.com/02catalytic_converters/02product/displayuniversal.asp?universal=45036

Muffler: Spintech Sportsman XLF 3332, 3” tall case (yes, I sprung for stainless, I’m a geek)
http://www.spintechmufflers.com/mufflers/street-mufflers/low-profile-street-mufflers/3000-xlf-round-sportsman-street-low-profile-/sportsman-street-3332xlf-2a-c-2a-s/prod_417.html

Note, I debated going with the Spintech “Cruiser” series where the muffler case is only 2 1/4" tall but after talking with the sales rep they said mine flows a bit better, runs a bit quieter, and I can’t really use the clearance since my cat is about 4” thick anyways.

Flexpipe:
2.5 x 6” with interlocked core (smoother flow) for some guy on ebay. Got the remainder of the mandrel bend tubing on ebay as well (0.062 wall) plus some stainless 3/8” pencil rod for hangers.

There’s also a 2.5” V-band between each component so it’s all serviceable as well. When I went to pull out the old exhaust I found the u-clamps had crushed the tubes to the point that I had to cut everything apart with my friend the angle grinder. No bueno.

The good news is that the Jeep feels a little stronger with the new setup so I’m happy. Now that I think about it, I’m not sure I’ve recalculated fuel economy since I built this. I should probably check that out.

It came out nice, if I do say so myself. I think I gained about 4” of ground clearance doing this. (The before pictures a few posts above).

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I built in an extra bung for wideband O2 tuning and I splurged on a fancy tailpipe exhaust hanger (again ditching the rusty *ish)
http://www.deedsengineering.com/EXHAUST_HANGERS.html

5DSC_0799Crop.jpg


One recommendation if anyone else wants to try this hanger. The bushing it comes with is not nearly compliant enough. It blew out immediately the first time the exhaust got hot when the piping grew via thermal expansion. I ended up redesigning the joint with a shoulder bolt and an oil-lite bushing so it acts like it’s on a linear bearing and grows about 3/8” fore/aft as it gets hot.
 
By the way, I drove this without the tail section one time on the freeway. Remind me never to run a turn down. The droning on the freeway was un-livable. So far as I can tell, dumping the exhaust under the car just reflects the sound waves off the ground straight back into the bottom of the vehicle.

If anyone is looking for a cheap exhaust I was momentarily temped by the low buck route from the DynoMax catback
https://www.google.com/search?q=xj+exhaust+dynomax&sourceid=ie7&rls=com.microsoft:en-US:IE-SearchBox&ie=&oe=#hl=en&rls=com.microsoft:en-US%3AIE-SearchBox&tbm=shop&sclient=psy-ab&q=xj+cat+back+dynomax&oq=xj+cat+back+dynomax&aq=f&aqi=&aql=&gs_l=serp.3...7862l8876l2l9094l8l8l0l0l0l5l234l1449l0j6j2l8l0.frgbld.&psj=1&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=25828f9a7ae54771&biw=952&bih=763

That said, I just couldn’t bring myself to throw those u-clamps back on the Jeep. I think I spent 3x as much in materials for my version, but it’s exactly how I wanted it so I’ll deal.

Underbody armor is next (this is the part where I kind of went off the deep end).
 
stainless is too rich for my blood. i dont think i've ever had a vehicle with an exhaust that rotted out in socal, so it doesnt seem worth it. my van is 21 years old with 287k and it's still solid and original. the jeep has 217k and is 20 years old, original except for a flowmaster muffler welded to the stock original pipes.
back east was another story....
 
that exhaust LOOKS real bitchin. but from the link you posted that is not a legal cat. jan of 2012 new calif laws states that the cat must be vehicle specific. and the one you listed is for a 96-97. i tried looking up a 99 but couldnt find a listing. but the 98 was different from the one you used. so you may find some issue with smog cert. especially when they see all that nice new stainless exhaust. when they look and see new exhaust work, they are supposed to (by law) run the numbers off the cat to make sure it is for your vehicle.
i would love to run a 2.5" cat but my 89 came with 2.25 and by law i cannot change the size.
 
Stainless is overkill from a pure functionality perspective, but I've found on my rx7 that I've had the enhaust on and off a bunch. Details like v-bands just make it so much nicer to work on.

In regards to SMOG I'll take my chances. I've spoken with the SoCal regional director of CARB on a few occasions to clarify topics in regards to engine swaps and I'm pretty sure I'm fine. There are two approved catalytic converters for my Jeep. The direct replacement unit ($500) and the universal version that's the same cat as the direct replacement but without the piping on both ends (~$200). I went with the universal but the one I picked is OBD2 approved (it's engraved with the appropriate CARB numbers.) The CARB approval is referenced in the part details of the link above.

I built the system in 2011, but frankly if you're doing the work yourself there's no way to prove the installation dates so the Jan 2012 criteria is meaningless unless you're a shop.

This all gets notably harder when you have a different engine under the hood.
 
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Does anyone know the difference between the early style Jeep exhausts & the later? I've looked up both of them, around a 50 dollar price difference but I have no idea what the physical differences are.
The exhaust shop I go to is cheap / very competent... if it is just hanging locations, I'm sure they can work it out just fine.
Will older parts work?
 
Mid Skid / Belly Pan

Part of my plan in building a pretty nice exhaust was that I wanted to protect it when I was done. Combine that with the fact that a lot of catalytic converters are getting stolen so thieves can recycle the platinum in the grills (lifted vehicles being especially common) and I decided the best thing to do was to make a full belly skid.

Covering the Jeep from rail to rail is a big area and I was worried that what I built would either end up crazy heavy (several hundred lbs) or else be far too easy to bend. I’d seen a couple skids that incorporated ribs but instead I decided to make a full double decker skid so I’d get the bending properties of an I-beam with the ribs just being webbing. At the same time I didn’t want to make it too thick least I lose all the ground clearance I’d just gained with the tucked exhaust. I also decided to make it full width and replace the BDS transfer case skid as that was easier than making the mid skid tie into the BDS piece.

After a little wandering in my local industrial metal supply to see what was easily available I went with two sheets of 3/16” 6061-T6 and ribs made from 1/2” by 1” by 1/8 wall rectangular tubing (also 6061). Having just played with welding aluminum on my gas tank skid, I decided to use riveted construction for the main double decker portion of the skid. This was both because didn’t want to lose the parent material strength properties at the heat affected zone and because warping might turn out to be challenging. That being said,since the rivets top and bottom had to be staggered to miss each other I ended up getting the hole pattern water jet cut after I designed it all in CAD.

Here’s where I started:

tCIMG3225Custom.JPG



The cutout for the driveshaft in the top skin is deeper because of the angle of inclination of the driveshaft. This was measured with rear axle at maximum droop with a extra inch clear just in case. It’s also worth noting that the driveshaft is not centered between the frame rails but rather offset by about an inch and half.

All rivets are 1/4" aluminum pop rivets with 1/2" heads. I found it’s hard to draw anything more than 3/32” with a hand tool so I bought the pneumatic version (Harbor Freight).

Then I started thinking about the fact that if I drag this over rocks too many times I could easily scrape the heads off the rivets and then have no way of getting the mushroomed end out of the ribs. Instead I went the hard way and proceed to counter bore all 100 or so rivet locations on the bottom side 1/16” deep so the heads were protected. I could grind them flush on the rocks and they’d still stay whole.

tCIMG3223Custom.JPG



Fast forward a couple hours later and the metal shavings were about an inch deep

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Here’s the internal ribbing:

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All ribs were all match drilled to the top and bottom skins using the water jet pattern as a template. Ribs took more than 400 holes because I had to drill a larger hole in the backside of each rib in order to have sufficient space for the mushroom to form as the rivet set. The big holes cut into at each end void between ribs were sized so I could shove a garden hose in one end and flood out any mud or sand that might accumulate through the other hole.

Once the main deck was complete I moved into the means of attaching it to the unibody rails. It had to drop below the exhaust and I wanted the hardware to attach from the sides of the rails. I ended up using a whole series of pull to set 5/16” rivet nuts.

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The sides are a series of tubes and plate (almost like mini boat sides) and I did have these welded to the assembled double deck structure.

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The two cut-out details on side are there to clear the e-brake cable mounting assembly. I decided it was simpler to clearance around that design a new bracket. Note, the rectangular spacers along each tube surface are just that. The unibody rails aren’t flat and this let me spread out the load as I want the lifting force to be primarily vertical with the small 5/16” hardware just keeping it in place.

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Weight… FYI: The BDS skid I removed was 8.5 lbs.

7DSC_0233Custom.JPG



On the forward end of the skid I used horizontal bolts to tie into the BDS cross member/trans support. While test fitting I found it was faster to through on a couple of bar clamps to be sure it was all the way forward.

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I ended up having about a 1/2" clearance around my muffler both top and bottom.

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And here’s the finished skid from front and back.

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This has about the same bending stiffness as a piece of solid aluminum ~0.813 thick. It’s kind of nice to not have to worry about high centering on anything. Now I just have to pay attention to the potential of hanging up on the diffs and rocks between the front wheels.

-Joel

PS If I ever throw in a different rear axle and it doesn't fit my skid, I'm going to be one sad puppy. This was easily a couple weeks worth of evenings.
 
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Figured if I was spreading out the load enough I wouldn't need them. Thoughts / examples?

The drip rails are already welded in 3/16" rectangular tubes so I contemplated tying those in.
 
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