Making a Boxer twin 2-1 exhaust...

[Lopperoon]

...by a novice with an angle grinder a few files and a mallet and vice!

First of all, some introductions.
I'm now 35, and I left the UK late 2007 to settle in Tallinn, Estonia, with my girlfriend. We stuck to our plan and got a dog and I stuck to mine which was to be still able to ride a bike through the cold, snowy winters. The result for biking all year in the Baltics and owning a dog was to buy a 2WD Ural 750 sidecar outfit.

We plan to ride this bike, with dog, to Kamchatka in a couple of years, as well as Cape Town some time after that and the Ural's big weakness for rough terrain, despite 2WD, is ground clearance, especially the 2-2 low exhausts.

I have a choice, stick to 2-2 and get upswept exhausts which can be hard with all the sidecar paraphenalia and bolt ons (20L jerry can and holder toward the rear) on one side, or go 2-1 with a high-profile exhaust on the outside, up by the mudguard.

The latter would be best for weight, tidiness etc, but hardest to achieve.

The plan for a 2-1 would be to use a Supertrapp end can on custom pipework. However, I am aware that tube length, exact curvetures etc can just as easily make you bike run like a dream with the pipes helping the cylinders on the A/C 750 Boxer twin working together, or turn it into an asthmatic heap with one cylinder making more power than the other, that ends up knackering your crank bearings!!!

Not what you want in the middle of Siberia!

So, quite simply: any thoughts, advice, experience out there to help me?

 

[MikeHalloran]

Buy the upswept pipes.

Move or modify the bolt-ons.



Mike Halloran
Pembroke Pines, FL, USA

 

[Lopperoon]

Problem is that the upswepts on the right, ie between the bike and the tub have the tub mounts, the 2WD lever, the final drive housing and the tub drive shaft, a pillion's leg and a 20L jerry can bolted to the boot of the tub to navigate round: not easy to get pipes that fit...

Meanwhile on the outside there is nothing to work round by comparison!!

 

[MikeHalloran]

Okay.
If you can buy 2-2 upswepts that will fit without the sidecar, do so, and put a dogleg in the RH pipe to cross it over to the left.

Do not be too concerned about unequal lengths and such in a street bike. Do be concerned about diameter and radius; just don't make anything smaller.

If you don't have ready access to a bandsaw, you'll end up with one arm like Popeye's, from making a thousand hacksaw cuts. Either way, you'll end up with a barrel full of pipes that don't fit and cutoffs of assorted sizes.


You'll also spend enough on tubing, elbows, tools and shipping to pay for a decent used Jeep... with a heater.



Mike Halloran
Pembroke Pines, FL, USA

 

[Lopperoon]

Thanks for the insights and advice.

Truth is I like the idea of a 2-1 and what it might allow for me to do, but I loath the idea of actually making it.

The advantages in almost every aspect of keeping 2-2 are not lost on me, but I would doubtless have a problem of relocating the jerry can, and that is something that I can not leave off, when considering the destinations we have in mind.

Other than diameter, could you give me any pointers on what sort of angles or radii I should stick too, or rather what is "too curved" for an efffective exhaust pipe?

 

[MikeHalloran]

First, the diameter of the '1' part needs to be 1.5x the diameter of each '2' part, and preferably a little bigger than that, just to keep the flow area constant or increasing.

It's possible to make a two-piece 'mitered elbow' by cutting a pipe at 45 degrees and rotating the ends, but for gas flow, it's a horrible idea. Slightly less awful to make it in 3 pieces, better in 7, or, best, buy mandrel- bent elbows, nice and smooth. There are usually several radii available in each diameter. Try to use the larger radii.



Mike Halloran
Pembroke Pines, FL, USA

 

[Lopperoon]

Mike, Thanks a lot for your time and input!!

I have a design in mind that could encompass the equal tube lengths that would be ideal, relatively large radii, and a single exhaust, but there will be a lot on kneeling next to the bike with flexi-hose before I know if it will work!!

I will still see if the 2-2 is an option: Supertrapp do very short end cans in some cases, yet back pressure can be adjusted with their disc insert system, so perhaps there is a solution there too!

Thanks again!

 

[miningman]

If I remember correctly, there was an outfit 25-30 years ago out of california called CC Products or something similar who sold a 2-1 system which I think was used by people like Reg Pridmore who successfully raced boxer twins..... dont reinvent the wheel if you can buy something off of ebay or similar.

 

[LadaTrouble]

I recently made a 2 into 1 for my 1987 BMW R65.It's not a good looker,but does the job.I have used a IDS2 Supertrapp,and the performance and sound is far better than 2 into 2 no matter what mufflers I used.