H,
2 into 1 or Siamese exhaust pipes are quite common and often favoured by sidecar outfit riders and as a tuning modification but.....
How many are designed to make the lengths measured individually from head tail the same?
How many have a clean internal joint to give max flow to the left hand pipe?
Some years ago the 2i1 on my wife's A10 started to split at the join where the left short pipe joined the righthand one. I pulled it off and to my surprise the hole for the joint was a very crude 'hack out' job probably achieved by drilling holes and then breaking the piece out. No attempt had been made to tidy it up to give a good flow. I tidied it up and welded it back together and it worked OK but had I improved the function of the exhaust? Perhaps!
This 2i1 was eventually replaced with an Armours HD chrome one which, although a bit fiddly to fit has lasted along time with the chrome staying good. As I spray the inside of new exhaust pipes with extreme heat resistant paint I had a look into the pipe to find a very neat and smooth looking welded joint. This looked 'proper' to me and I was happy with it.
Having to take a 2i1 off my A65 I had a look and found a quite rough finish to the join potentially impeding flow.
Does the quality of this joint make a difference to the performance of the whole exhaust system and particularly the left hand side.
The original BSA A65 Siamese pipes had a long section where the two pipes merged together. EVERY aftermarket pipe I have seen has not been made the same and does not have flow in mind. I worked a while fabricating exhausts for cars but the theory carry's on through to bikes too.
When I made my own 2-1 I copied a genuine clubman pipe but shortened it to a tuned length the RHS pipe measures 31" along the long side of the pipe (the outside of the curves) the left hand measure about 34 or 35"
When I first made it, I build a step on the short side of the pipe, this prevents gas flowing back into the cylinder. Carburation took some working out and the bike sounded odd when ticking over - sounded like a 90° crank was fitted even though it's a 360° still but it gave the best torque and top speed the bike had seen. It even had more speed left in the bag.
Hi,
I will measure the pipes to see what the difference is and if I buy flexi extension for my power drill I may be able to remove some of the roughness and protrusions at the join. I would think that the outer part is more important and it looks like it will be easier to work on. Perhaps the inner interference will serve to disrupt the return pulse.
Unity Equip list a two in to one that joins under the engine so the same length for the two headers but a bit impractical if a main stand is wanted.
Looking at car exhausts were there may be a 4 into 2 into 1 with a succession of collector boxes each increasing the cross section of the pipe. The result, I assume, is that the capacity of the pipe remains the same and/or that the pressure and velocity reduce.
Does this help with scavenging? A knock on from this, should the a two in to one have a bigger cross section after the collection point say from the 36mm of the headers to 50mm for the tail?
Perhaps a bit difficult to accommodate on the style of motorcycle of the day.
Dave.
This was my pipe when I made it. The black one being what I made, the rusty chrome one being the original clubman pipe. You can see how long the merge point is, it's as though you overlayed the shape of one pipe on top of the other. As I say it does work and it works much better than any aftermarket Siamese type I have tried.
If you were to make one Dave, I'd use 1 3/8" down pipe from the head, you could squash a 1.5" pipe to make an ellipse shape where the two pipes meet. Not a lot in size difference but it's that smaller size which makes the 69-on Firebird so much more powerful and tractable compared to the Lightning. Least that's what I intend to do with my next exhaust build. Anything smaller than a 650 (say an A50) would benefit even more over the standard pipe.
My 823 responds really well on the standard pipe size so that shows how big it is for a 650.
Hi Allan,
Some pipe measurements:-
length of joint weld 3 3/4"
Outside run on main pipe 39 3/4" to head
Outside run on short pipe 41 1/4" to head
entry to silencer is 1 1/2" external and 2 1/4" in total so 3/4" internal
pipe extends 4" in to the silencer in total
so the pipe extends 1 3/4" in to the silencer body
With a 31" pipe how did the silencer fit with footrest etc?
I think part of the problem is that the short left hand pipe has to run to the front of the frame loop and to get it shorter and behind the frame, ala A10, would result in a very tight turn. If this could be done then the curve of the righthand pipe could be tighter and thus be a shorter length.
Dave.
Hi Dave, I think the oif Siamese pipe is identical in appearance to the A10 style.
I think the first starting point would be to slide the silencer back off the pipe by 2". I found my old Armours standard pipes were too long and it killed power at top end. Infact I found their silencers too restrictive too. But that's another story. I slid the silencer so that it only entered as far as the clamping section on the silencer would allow - this was about 2" give or take. Infact one side was longer than the other. This restored a decent top end speed. I then shortened the pipe knowing that the improvement would continue, so marked it out with tape and got the angle grinder on it.
The Lightning I am running with rear sets, it makes the bike much more comfortable over long distances and less strain on my back. But I have fitted the stock forward mounted pegs and it doesn't bother it any. But I am running a megaphone so the taper of the pipe follows the frame rail, the silencer is also tucked in. If your running the standard pre oif style silencer, then you may see some restriction on location.
Hi,
Looking at Unity Equip, they do a 2to1 that meets almost under the engine and then exits right to accommodate the centre stand but the on for the BSA does not. I found this one on an A65 that accommodates a centre stand but no manufacturers name.
I would guess that Unity Equip would come up with an altered BSA one but at what cost?
The first thing to determine is if the outcome will be worth the effort.
Dave.
I very much doubt you would see any difference Dave, as I mentioned not having the downpipe so far into the silencer will have the biggest effect.
Hi Allan,
I have asked Unity if they do a variation for when/if I need new pipes but stainless ones last for ever.
Currently the pipe goes about 1 3/4" into the silencer so looks about right from previous threads.
Dave.