Routing exhaust through frame cross members?

[redss86]

I am finally getting back to working on my Monte again. I have rebuilt the perimeter frame out of 2x4x0.125 wall tubing. I have a cross member at about the middle of the frame for my truck arms. Then I have braces going forward basically from the truck arm mounts to the front torque boxes on the frame (see attached pics). I am thinking I want to some how route the exhaust through these by welding in some round tubing. I am just a little unsure on what size/ thickness to use. I am figuring on running oval exhaust, but is still think I am going to want the extra clearance. So if it goes through the braces, it will give me plenty of room. The exhaust is going to have to exit in front of the rear wheels, because it would be impossible to get it over the axle with the truck arms, panhard bar, and gas tank setup.

Thanks for any and all suggestions. I was thinking about using something like 4"x0.250 wall? Not sure what I need to maintain adequate strength?

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[j-c-c]

So the question is, you want to run the exhaust thru the braces, not the perimeter 4x2 frame, correct? What size are the braces, and what are the expected loads on those braces (4?), compression, bending, torsion, or expected combination? And desired exhaust tubing size for oval or round?

Clean/robust design BTW

[redss86]

Correct, wanting to route it thought the braces. The com out under the 2x4 frame with a Nascar "boom tube". The braces are all 2x2x.125. I don't know what kind of loads they will see exactly. The one straight across is the mount for the truck arms so it will see quite a bit of load. The two going forward, are just extra reinforcements to keep the other from flexing. The exhaust is planned to be oval like this:

[redss86]

Well, I went ahead and made some pieces, and welded them in place. I have only done the rear two, and have the pieces cut for the front bars. I ended up getting a hold of a 3 ft piece of 4-1/4 x 0.250 dom tubing (it helps having a machinist for a brother). I cut two 2" pieces, and used a torch and vice to compress it into an oval. It worked out really well, the pieces of oval exhaust that I have just BARELY fits in the sleeves, but it is equivalent to 3.5" round. I feel I can go down a size in oval tube to 3" equivalent, and be just fine. I will just have to make custom pieces to step up to the Boom Tubes.

Using a plasma torch I cut through 3 sides of the cross member, and slid the piece into the cut before cutting the last side. I then TIG welded it in place (only doing one side at a time). I am debating whether to put any extra gusseting around the pieces. I had to take the tube to a local metal fab shop to cut the tube at the angles I needed. My little band saw wouldn't cut at the angle I needed. Now I just have to get them shaped and welded in place. Let me hear your opinions, good and bad. The bottom 2 pics are with the frame upside down for easier welding.
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[j-c-c]

I'm guessing here, but I don't see a lot of vertical loading being placed on the area of your oval pass thru's. They look nice, I might have been tempted to drill some lightening holes, but that could be risky, and for little gain. What i do see that I would suggest is two additional braces that basically continue forward, on the front side of the exhaust cut out crossmember. They would IMO be in a continuous straight line with the two existing splayed out rear braces. I suspect this area absorbs/handles a lot of the thrust loads of the rear axle, and help support the cantilever of the oval exhaust pass thru, and the current load path is partly, an inefficient z design. Just thinking out loud.

Stop the presses, I'm driving around this afternoon, and "truck arms" pops into my head, Oops, sorry, they also do transfer torgue forward into a vertical component at this crossmember, depending on how stout your combination is, you may want to gusset say on the top those oval tubes. And if you added the previously suggested extra small braces I mentioned, no more needed then a 14g material, IMO .

[redss86]

I'm guessing here, but I don't see a lot of vertical loading being placed on the area of your oval pass thru's. They look nice, I might have been tempted to drill some lightening holes, but that could be risky, and for little gain. What i do see that I would suggest is two additional braces that basically continue forward, on the front side of the exhaust cut out crossmember. They would IMO be in a continuous straight line with the two existing splayed out rear braces. I suspect this area absorbs/handles a lot of the thrust loads of the rear axle, and help support the cantilever of the oval exhaust pass thru, and the current load path is partly, an inefficient z design. Just thinking out loud.

Stop the presses, I'm driving around this afternoon, and "truck arms" pops into my head, Oops, sorry, they also do transfer torgue forward into a vertical component at this crossmember, depending on how stout your combination is, you may want to gusset say on the top those oval tubes. And if you added the previously suggested extra small braces I mentioned, no more needed then a 14g material, IMO .

Ok, so I finally got back to working on this again (wife actually told me to go out and work on it). I just finished putting the short braces in that you suggested. I have not put the gussets in that you mentioned. My goal is a primarily spirited street driven, with the occasional auto cross, and road course. Planning on a twin turbo ls6 backed by a Viper t56, and a Ford 9" with a 295-315 rear tire. Max power goal is around 600-700 rwhp (maybe more?)

Here are some pics. Let me know if the gusseting is still needed.
https://static1.pt-content.com/images/pt/2015/03/20150317_221902-1.jpg (http://s71.photobucket.com/user/jmarti81/media/Mobile%20Uploads/2015-03/20150317_221902.jpg.html)
https://static1.pt-content.com/images/pt/2015/03/20150317_221839-1.jpg (http://s71.photobucket.com/user/jmarti81/media/Mobile%20Uploads/2015-03/20150317_221839.jpg.html)
https://static1.pt-content.com/images/pt/2015/03/20150317_221919-1.jpg (http://s71.photobucket.com/user/jmarti81/media/Mobile%20Uploads/2015-03/20150317_221919.jpg.html)
https://static1.pt-content.com/images/pt/2015/03/20150317_221933-1.jpg (http://s71.photobucket.com/user/jmarti81/media/Mobile%20Uploads/2015-03/20150317_221933.jpg.html)

What about putting these in here? They will also be flatten some to make them more oval. I will be using the same 1/4" wall dom tubing.
https://static1.pt-content.com/images/pt/2015/03/20150317_222029-1.jpg (http://s71.photobucket.com/user/jmarti81/media/Mobile%20Uploads/2015-03/20150317_222029.jpg.html)
https://static1.pt-content.com/images/pt/2015/03/20150317_222042-1.jpg (http://s71.photobucket.com/user/jmarti81/media/Mobile%20Uploads/2015-03/20150317_222042.jpg.html)

Thanks for any and all suggestions.

[jaybee]

IMO the short braces are key to that whole part of the frame. They spread the loads directly throughout that area. It looks as if your through-tubes stick farther out the bottom than the top. If that's the case you might consider some sort of gusseting to help that tubing keep its shape under load. Maybe some square tubing pie sliced so that it would make a wedge shape from the bottom of the crossmember and reinforcing the curve of the tube.

[redss86]

Yes the ovals are off set to the bottom. I had to do that for floor clearance.