first exhaust fab. part1. advice?

[mag2367]

So in my thrifty attempts to find cheap diy projects for the truck i managed to pull togeather some supplies from my shop and a little dumpster diving at the collision center.

Ive got tons of exhaust clamps, hangers, flanges and now two exhaust systems; one from a porsche cayanne and another from an audi s4. Both are dual pipe systems, i got pictures but cant figure how to load from my phone, anyways they both got a couple bends but a lot of the pipe is good. Audi pipe is 2.5" almost everywhere and the porsche has a lot of 3" and theres like 5 more exhausts still in the trash that i can rat-f&*k

For the sake of saving cash and not investing in high flow cats or headers YET, my current strategy is just take the new pipe back to the primary cats, the manifolds and cats need replacing soon but not yet.

I went to the local dump&recycle and found a busted up 150cc scooter, which i took and traded for a perfectly good 120v lincoln mig welder. I dont have gas or the nessesary fittings to hook up gas but it came with a spool of flux core, which will be messy no matter what but as long as it works i dont care about how clean it looks, my plan is to practice with the junk pipe first and get confident with the machine, been youtube watching so i know how it should look at least haha.

I found a deep cut band saw on the side of the road a month ago, ovbiously fell off a truck but no contact info so its mine now, i was planning on lobbing off the resonators and mufflers and all those other metal boxes and just keep the tube but before i cut i was wondering if i could use those at all or if i am correct in regarding it as scrap.

Any tips advice or wisdom is appreciated, not really trying to achieve any noticeable gains but i need a new exhaust as mine is crumbling away, and this is something fun i get to build which might sound cool in the end. I think i understand the basic function and design of a correct exhaust, but as i am intending to frankenstein the thing i dont expect to know exactly what the final product will be, so im fairly open minded. Any thoughts, comments or concerns? I will figure out pictures by tonight...

[speedfoos]

If you've never done exhaust before it can be a small pain. Best advice is to work from the tail and work toward the engine when you go to weld everything up. Tack weld while it's in place as much as you can so it doesn't shift too much when you go to stitch it all closed and tighten the clamps completely during mock-up (it's a pain but worth it) because that pipe will move if you just finger tight them.

Other than that, take your time and test fit, test fit, test fit!

[Spelvin]

Sounds like good scrounging skills. Is all the pipe the same size? Something else you may want to find is a tailpipe expander. With that you can fit one pipe into the other then weld. Also during mock up if you mark the pieces with a sharpie you can then line things up and weld outside the vehicle.

Keep us posted and get some pics up.

[mag2367]

Thanks for info, that tailpipe expander + weld is a good idea, and ill make sure to start from the tail and work forward. I didnt think about the twist and misfit factor,but will take extra care to tact the pieces togeather when i get the angle right. I still need to drop by old exhaust and design the pattern i can make with my supplies, i want the same tip exit point and fairly decisive in wanting a single exhaust, i was thinking of using the 2.5 pieces until the y-pipe and then going 3" straight back, ill post more informative details about my situation tonight when i get everything togeather.

[JaydenH]

With the flux cored wire, I would try to expand one end of the pipe you are going to weld and fit it over the other. You can concentrate your heat on the top piece and tie in to the bottem. Flux cored really likes to "dig".

[mag2367]

Ok good tip for the practice pieces, ill try my best to work the top down, im guessing ill be holdibg two pieces under the truck 'yup that looks good.' Tack it and move onto the next piece and so on, drop it, weld it and hopefully it all lines up at the end

[joefrontier2]

personally I would try not weld anything but flanges to the pipe. For pipe to pipe I'd go with an expanded flare with a really nice clamp. Unless you cannot get the pipe bent then you would have to weld.

Remember you will need a flex braided piece in the center just before the dual exhaust from the right goes perpendicular and dumps into the Y. Do what the rest said. Tack weld and mark everything.

[speedfoos]

I personally hate the u-bolt exhaust clamps and always weld unless I flange. If I ever do my exhaust again, it's getting all v-band flanges. Those things are sweet to work with if a little spendy.

[mag2367]

So i took the pipe cuts that i have remaining from their original format, and i did a rough layout under the truck according to the oem exhaust. Its looking pretty good and i managed fairly well for a one time grab, so i will get the remaining pieces that i will need this week.

what is the purpose of that braided flex pipe, i see that it is at the y joint on my stock system?

I collapsed the layout for the pictures, so that more would show in each photo. it was dark so i apologize.

I've got a couple more bends which i think ill need to line up the flanges, and i need about two more feet for the drivers side, but ive got a little room to play around with the rest. the ovbious breaks are what im dealing with as far as welds or clamps like joefrontier had mentioned, i think i've got two of what you are talking about? pictured but if those will work for straights without welding that could save time and effort, i would just have to worry about the tight ones. and i can get a bunch of those at work...

[joefrontier2]

Flex pipe is used to give flex in the exhaust ya duh.

For instance when you rev the engine it can twist from one side to the other. The twisting motion, if the two exhaust sides would connected with rigid steel would eventually fail at some point. Also when you are driving off road or over bumps the frame can also flex differently than the motor which allows the bolted on exhaust to flex at the flex pipe. Better to buy one than to have your creation fail.