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Building An Exhaust


someonestolecc
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Gday,

I'm going to attempt to build an exhaust for my r31.

Questions:

1.)

Is it better to get straight pipe and do crab bends like the J style intercooler pipes or go to liverpool exhaust or somewhere and buy some bends?

As far as I can see the crab might be cheaper and harder to mess up the bends, but take longer (I don't have a band saw, it'd be done with an angle grinder). Also to sand down the weld marks on the inside might make it weaker?

2.)

How do you join pipes? Last time I did it I hammered one edge out a little so it would fit over the other part of pipe. Obviously so the bigger one went into the smaller from front to back so the exhaust gasses wouldn't be slowed down too much.

Having said that is it better to just have them together without overlap?

3.)

How do you weld hangers onto the pipe? I would assume it'd be best only to weld them to flanges, otherwise I'd probably make a hole in the pipe.

4.)

What thickness/grade of pipe should I be using? Is there anything I should know about purchasing the right piping? I know I can just walk into the zorst shop but thought I'd ask.

5.)

Anyone have tips on design technique? I was going to take the old zorst out and copy it, checking each section as I went on the car. I'd purchase a normal single down/front pipe, then weld a flange to a bit of pipe, attach it take it off, copy the old etc etc etc etc. Anyone have any tips?

I think that's it. Thank you.

PS great section :laugh:

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1) there are usually only about 4 bends in the exhaust, so at $20 a bend for stainless you would be better to use them instead of the section bends, considering the time it would take, as well as the limited accuracy you would have with an angle grinder. If with stainless you would want only a gap between the pieces that is smaller than the filler wire you will be using. you can do it, but the trouble with increase and neatness will definately be affected.

if you decide the crab style, then use 7 degree's of less for the angle of the cuts - any more and the matching of the end pieces becomes ugly,hard to weld, and a flow restriction

2) butt joints will be best, once again its neater, but true it would be harder to weld neatly but would look better in the long run and no worry of affecting the flow

3) most hangers are welded onto the side of the exhaust where needed, just ensure there is no burn through or holes. as well and sufficient area of weld to prevent any cracking since this is where the weight is taken from. also from what i have seen, try and triangulate the support so there is more coverage

4) up to you on what you want to pay for the grade of stainless, just remember to match the filler with the grade of steel you use.

5) it would be easier if you did it in sections, but it really depends on why you are changing it in the first place. If your happy with the design and it seems to flow well, then i would copy it.

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tom,

don't even try lobster. just buy bends :happy: take your exhaust off and note what bends there are and buy the same in steel. liverpool exhaust are really cheap.

also ins't your welder a arc welder?

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yea i did this with my r31, mine was very low so i ran the 3 inch under the diff, so yea with any normal 31 its up and over the diff which will be a pain in the arse with straight pipe cut and shut into bends. I made mine out straight pipe. if i was to do it again i would have bought bends. did the job well tho.

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Thanks for the comments guys.

The exhaust will be mild steel. I don't really care for stainless - it's a r31 so if it gets the job done well the cheaper the better.

Ok, so the section bends are out.

What's a butt join?

r31's have crap exhaust path, have to go over the diff. I couldn't go under my car would be illegal and I'd wear it through scratching it. I don't like th idea of it flowing up and over (it's a fair looking restriction) but what can you do other than get a s13/a31/r32....

Nic, no idea. It's Jacek's. I'll just try to use it, it seemed to work last time <shrug>

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Thanks for the comments guys.

The exhaust will be mild steel. I don't really care for stainless - it's a r31 so if it gets the job done well the cheaper the better.

Ok, so the section bends are out.

What's a butt join?

r31's have crap exhaust path, have to go over the diff. I couldn't go under my car would be illegal and I'd wear it through scratching it. I don't like th idea of it flowing up and over (it's a fair looking restriction) but what can you do other than get a s13/a31/r32....

Nic, no idea. It's Jacek's. I'll just try to use it, it seemed to work last time <shrug>

butt joint, there are different types, but have a look in the welding 101 thread here http://www.skylinesaustralia.com/forums/in...howtopic=156412

the post by JAS-25T has a few PDF's one of the the TAFE one, has an outline of different butt joints.

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For all my exhaust I just buy a few 90* bends and a length of straight tube.

BMWRB20_0040.jpg

Exhaust for an RB20 into a BMW

RZN160_0067.jpg

Exhaust for my Hilux

mate i did all mine at home on the floor 3"mandrell bent pice of piss if you want a look at it send me a pm or phone me or ill doo it for you exhaust that is ! ph 040902772three

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  • 1 month later...

purge it?

You don't need to purge it if you get your penitration right. As long as you don't have dags on the inside of the pipe, you will be fine.

the system looks good!

Edited by psi
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  • 2 weeks later...

Got a question for all you tech heads out there.

Does anyone have any pics or diagram of a 1 into twin pipe setup? I've got the pipe and want to fab but unsure of how to get 1 pipe into twin pipes.. they are all the same diameters. I've sat with a bit of plastic pipe to try to get the angles but I can't seem to do it! :\

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  • 1 month later...
Got a question for all you tech heads out there.

Does anyone have any pics or diagram of a 1 into twin pipe setup? I've got the pipe and want to fab but unsure of how to get 1 pipe into twin pipes.. they are all the same diameters. I've sat with a bit of plastic pipe to try to get the angles but I can't seem to do it! :\

You can buy 2-1 collectors.

Or notch to match and weld it up you self. Hard to explain, you just got to sit down and try it.

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i've tried to think of ways to make the Y collectors but even after looking at pics of one like below, still a bit hard to work out the angle and cut needed to bring them together and get the single pipe to match perfect.

post-5157-1182488992_thumb.jpg

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doesnt look like it would be too hard to make one up (says me who probly couldnt lol)

all you have to do is cut it from the very middle of the pipe up along the length of it, and any angle towards the side really, as long as its even on both sides if you get what i mean? thats for collectors with the same size pipe joining it eg: 3 inch pipes into 3 inch collector

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  • 10 months later...

ill have to get some pics up of my exhaust me and a mate did. its a 3 inch stainless steel tig welded all mandrel bent. theres a fair bit of f**kin around all up it took us around 10 hours to do. its in an r31 too

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bLaQ.bOi got it spot on you do need purge that is if your using stainless, If you think you can control this with the amount of penertration that just means your not getting a full strength weld.

As for the collectors use the link above, and to get the right dia multiplie the dia by pi eg: 3" = 76.2 mm

so that 76.2 x 3.141 (3.141592654) =239.3893602 after getting this simply measure out that lenght on something to wrap around the 2 into 1 joint and cut, use a flairing tool or pressing tool to bring it to a nice round shape and bam thats it! happy fabin :bomb_ie:

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  • 4 months later...

when i get some time i want to modify my exhaust by putting in a dummy muffler with a hidden bypass as close to the front of the exhaust system.

i want to do it in a dummy muffler because bypass valves are illegal in perth and i want to hide it.

can any body see a problem with this?

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