1978 XS11 inside exhaust diameter?

[scrapvalue]

I need to now the inside diameter of the stock head pipes on a 1978 XS1100.

Thanks

[CaptonZap]

What are you up to, tuning the exhaust?
I don't know about the 78, but an 80 has an inside diameter of about 1.127, plus a coat of carbon on each side.
That was measured about an inch and a half into the discharge end, before it flared out to meet the outer pipe. (Where the two are welded together)
The parts list shows a part number of 2H7 14631-02-00 for the 78, and a 4H3 14631-00-00 for the 80. (This was for either #2 or #3 ).
So I would imagine that the pipes would interchange. Which would make them the same, dimensionally.
Let us know what you are up to, huh?
CZ

[scrapvalue]

Actually I want to try building an extened set of straight pipes.
I made a set for my CB750 build and the work awesome.
I was able to just slip 1 1/2" exhaust pipe over the head pipes.
The XS11 pipes are a larger diameter so I am wondering if I can find the right size pipe ot slide the inside the XS head pipes.

Don't really want to cut my pipes until I know if I can find the right size pipe form the project.
The pipes on my bike were all rusted out in the rear on the bottom.
I cut them off right behind the rear foot peg mounts.
They sound o.k. and they aren't to loud, but I really want to try to build my own.

I am able to tune them by length and restrictor washers welded inside the ends.

I am hoping to find another set of head pipes for the build.
If anyone has an old set, I would be interested in purchasing them.


Here is a picture of my XS with the hard bags.
http://i1112.photobucket.com/albums/...0528111848.jpg

Here is a picture with the bobber rear end.
http://i1112.photobucket.com/albums/...ue/xs11010.jpg

Here is a picture of my CB750 with the straight pipes.
http://i1112.photobucket.com/albums/...alue/ksl-1.jpg

[natemoen]

Actually the stock headpipes are something more like 3/4"ID. The double wall really shrinks the interior of the headpipes. I can check later on my pipes.

[CaptonZap]

Actually, the inside of the stock pipes is 1.127 in +/-, and the outside is 1.5 in.
I don't know if Scrapvalue was aware that they are double walled or not, but it might make a difference to his calculations as to what length to make the pipes.
The inside of the # 2 & 3 downtubes at the bottom is 1.291 inches in inside dia for about an inch going back in, and then gets smaller to the 1.127 inch dia.
SV, take the pipes apart, and inspect them closely before you make any solid plans.
Finding 1 1/4 inch OD tubing and mandrel bent ells will be a challange, and the wye fitting of the stock pipes is hard to improve upon.
Good luck, and keep us posted. CZ

[cywelchjr]

Sounds like you have the right idea with building something into those pipes to create some back pressure though. Just be aware, almost nobody has had success with getting better performance than a good stock exhaust. Of course by the same token, those are very hard to find so you have to work with what you can find. Those Yamaha engineers back in the day appear to have done a REAL good job of tuning these intake and exhaust systems for best all around performance. The best most have been able to do without pretty extensive work was to move the power band either up or down the RPM range at the expense of the rest of the range.