Dogbytes' R80 ST project

I'm no expert on exhausts but from a fluid dynamics perspective fabricating up tight bends from short sections is likely to cause poor flow characteristics as I would have thorght you would struggle to debur and clean up the inside on such a small tube

For a circa 40mm tube I would have thought the best option would be to form a custom bend from a straight section of tube by placing a series of cuts on what will be the inside.
atleast you then stand some chance of being able to clean the inside edge before forming and welding up as a bend.

This would also give you a smoother outer radius.
 
blueranger said:
I'm no expert on exhausts but from a fluid dynamics perspective fabricating up tight bends from short sections is likely to cause poor flow characteristics as I would have thorght you would struggle to debur and clean up the inside on such a small tube

For a circa 40mm tube I would have thought the best option would be to form a custom bend from a straight section of tube by placing a series of cuts on what will be the inside.
atleast you then stand some change of being able to clean the inside edges before forming and welding up as a bend.

This would also give you a smoother outer radius.
Click to expand...

Eh,

you make the exhaust up using pre formed bends, they are welded on the straight bit after the bend, there's no need to deburr there's no burr on the pipe!
 
ianboydsnr said:
Eh,

you make the exhaust up using pre formed bends, they are welded on the straight bit after the bend, there's no need to deburr there's no burr on the pipe!
Click to expand...

"Unfortunately, practicality, and the positioning of other parts, means that the exhaust routing is going to be tight behind the gearbox so there will have to be some awkward bends - but that's life."

If a standard radius bend works great, but if you can't get one tight enough then you have to make one from chopping chunks out of a preformed...i.e. lobster bends.

http://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRw&url=http%3A%2F%2Frennlist.com%2Fforums%2F944-turbo-and-turbo-s-forum%2F738841-lobster-bends.html&ei=NIp1Vev5KoyBUb28g9gE&bvm=bv.95039771,d.d24&psig=AFQjCNF2V4TLITIKqxn6bhSZ_PTuvojLpg&ust=1433852830940930
 
There is a short initial straight section as the primary pipe leaves the cylinder head, then a large radius bend, followed by a straight section to the rear of the gearbox. This is very straightforward and can be done in one hit by the pipe supplier.

The next problem is where the pipe joins and turns from two, equal length, 1⅝" pipes to one 2" pipe. That has to be as long and gradual a join as possible and has to fit behind the sump before emerging somewhere on the left side to join with a short length of 2" pipe to meet the silencer.

It will be done with standard bends (they can be had in various angles/radii so the planning is the difficult bit) and they'll be TIG-ed together. If I flood the inside with argon, as well as shielding the torch side, it should prevent to much crud from forming and minimise awkward cleaning tasks afterwards.
 
I digress...

Just a thought. For all those who think airheads should be left just as BMW made them - look how many people those of us who think otherwise are helping stay in business! :clap
 

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Dogbytes said:
It will be done with standard bends (they can be had in various angles/radii so the planning is the difficult bit) and they'll be TIG-ed together. If I flood the inside with argon, as well as shielding the torch side, it should prevent to much crud from forming and minimise awkward cleaning tasks afterwards.
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Not sure whether this will help you or not or you may already know this so appologies if you do.

Stainless tube is commonly manufactured according to a "schedule" much like any tube standard. In the case of exhausts I would imagine you would be using schedule 5 or 10 at the most.

The bends/elbow are available in various standard radii as you say generally anything 1 to 1.5 I would tend to call and elbow anything 2+ would be a bend

This site might help you as they list the OD&ID of standard schedule tubes and have details of the elbows and bends.

http://www.nero.co.uk/Catalogue/Butt-Weld-Fittings-Schedule-10S-304L

Looking forward to seeing the pics.
 
These guys have a good reputation if you wanted someone else to make them http://www.osmc.co.uk/ or you could contact Pruster on Advrider. He's in Holland and makes some lovely parts.

Nice exhausts

IMG_8909.JPG
 
You'd think, wouldn't you...

Okay, exhaust, there are four requirements; 15/8" o/d, 1.2mm wall thickness, 304 stainless, 180 degree bends. I've tried 9 people now and most can fulfil two of the criteria, some even three of them but four? No way Jose! :confused:

Tomorrow I redesign the system. This is why I'd like to have been able to do my own pipe bending...
 
Most custom systems are flared at the header to suit the exhaust ports before dropping down to a standard tube size. In stead of buying tubes and bends designated as exhaust tubes have a look at hygienic tubing, sometimes called dairy tubing.

these guys are in Somerset http://www.pipeline-products.co.uk
 
Canuck said:
How are 180 degree bends useful? I'm just trying to visualize it...
Click to expand...

I wanted to do a smooth 180 degree bend, with a centreline radius of about 120mm, immidiately after the pipe leaves the head. Some people can do this in one hit whereas others weld two 90's together. The problem with the latter is that, if there is any smoothing out to do on the inside, it's difficult to get to.
 
Rob Farmer said:
Most custom systems are flared at the header to suit the exhaust ports before dropping down to a standard tube size. In stead of buying tubes and bends designated as exhaust tubes have a look at hygienic tubing, sometimes called dairy tubing.

these guys are in Somerset http://www.pipeline-products.co.uk
Click to expand...

I'll look into that. Richie has suggested 1 5/8" at 1.2mm wall thickness and a 31" header length. I'll take his advice on that because he knows better than I do. Actually trying to fit in a 31" header is quite difficult! 1 5/8" is, as I'm sure you know, a standard tube - just not for BMWs. I think I can probably get what I need but I'll have to order from two separate suppliers that's all.
 
Today I found a local firm that is going to cut out the backplates for the rearsets. They'll be waterjet-ed out of 10mm 6082 aluminium plate.

Waterjet cutting can be very accurate so there should be very little to do when I get them back (tomorrow or Friday - they had the 6082 in stock). I'll just need to finish the holes to the correct sizes, countersink them and put a bit of a shine on them, - and the , maybe, get them anodised.
 
I'll order the exhaust components today, there are 18 of them - that's a lot of welding!

Apparently this is the way to go for welding this kind of thing, a CK Gas Saver the screen is supposed to give a better coverage of shielding gas and the large Pyrex cup means you can see what you're doing and you get better shielding behind the weld. We'll see soon enough. Can't see it saving much gas though…

Right now I'm measuring up for the battery box and switch panel - I'll get them water-jetted when I pick the rear set backplates up.
 

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Picked up the water-jetted rearset backplates today, great service but I was a bit disappointed with the quality of the work. However, as I hadn't used this firm before, I did leave enough extra meat on the drawing to compensate - it just means a lot of extra finishing. Anyway, the brake side is almost done so I thought I'd assemble it - just to have a little look!

I'll do some better pics when they're finished.

Pedals and pegs are from Harris. I'd like to have made them but time is of the essence now. Besides, this way they're off the shelf items should a mishap befall them! The gearshift side is, anyway, the brake pedal will need some modification...
 

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Gear selector thingy...

Are there different kinds of these? This one will only go on in two positions - neither of which particularly suit me. Just wondered whether there were others before I start making one.
 

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Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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