stock head pipe dimensions on 78 XS650E

[zrx1100]

As I am now looking to further tune the exhaust on my project: https://www.xs650.com/threads/700cc-kit-with-a-shell-1-cam-in-a-78xs650e.65405/

I took dimensions on the stock headers that may be of interest to some.

Overall the ID is 1.15” and the length is 29.5”. At the exhaust port there is an insert that almost looks like a “torque cone”, but I don’t think it does anything as the diameter of the pipe and the cone quickly reduce to 1.15”.

At the exhaust port of the head

at the muffler facing end

One thing I notices is that the “shoulder” beyond the gasket ring that fits into the exhaust port is only 8mm (0.32”)

which is not long enough to bridge to the depth of the cutout pocket inside the port itself and to ensure a smooth transition from the port to the headpipe:

The depth of this pocket is 15mm and is taken well into account by the design of the exhaust optimizers from yamahaxs650.com

I will be soon testing 1.75" headers with these exhaust port inserts and MMM's torque peak optimizers on my 700cc build. The 1.75" headers without the mods did not do well for me.

 

[5twins]

Yes, this motor likes a small diameter pipe up at the head, at least for a couple inches. I added the ends of old stock headpipes to my 1.5" headpipes. I did it to get them to seal into the head better as they leaked like crazy at first. But it seems I also reaped the benefits of an AR insert too. I also added a pipe ring to finish filling that step in the head .....

My other 650 has the 1.5" headpipes as well, but without the inserts. I think the one with the inserts runs better, so it seems they help even on 1.5" pipes too. I may make up another set for this 2nd bike.

 

[5twins]

Another thing I may try is "D port" inserts. These are the ends of XS500 headpipes. With a bit of work, I think I can get them to fit into the 650 head .....

 

[zrx1100]

Yes, this motor likes a small diameter pipe up at the head, at least for a couple inches. I added the ends of old stock headpipes to my 1.5" headpipes. I did it to get them to seal into the head better as they leaked like crazy at first. But it seems I also reaped the benefits of an AR insert too. I also added a pipe ring to finish filling that step in the head .....

View attachment 260599

View attachment 260600

View attachment 260601

My other 650 has the 1.5" headpipes as well, but without the inserts. I think the one with the inserts runs better, so it seems they help even on 1.5" pipes too. I may make up another set for this 2nd bike.

that is a very nice solution, 5T. You closed the gap in the port/pipe transition and allowed for high speed of gas flow at the port. The optimizers from yamahaxs650, mikesxs and Heiden seems to all be very similar and have the diameter at outlet 1/16" smaller than that of the stock pipe. I will see how the dyno numbers look for my latest configuration with MMM's TPOs (1 3/8" OD. 1 1/4 " ID) and may enlarge the diameter of the port optimizers i have.

 

[jaybar6]

Yes, this motor likes a small diameter pipe up at the head, at least for a couple inches. I added the ends of old stock headpipes to my 1.5" headpipes. I did it to get them to seal into the head better as they leaked like crazy at first. But it seems I also reaped the benefits of an AR insert too. I also added a pipe ring to finish filling that step in the head .....

View attachment 260599

View attachment 260600

View attachment 260601

My other 650 has the 1.5" headpipes as well, but without the inserts. I think the one with the inserts runs better, so it seems they help even on 1.5" pipes too. I may make up another set for this 2nd bike.

Hi, 5Twins: That's a great idea you have there. You have smoothed out that inner interface with your own device. Did you machine it on a lathe?
It begs the question why has Yamaha left that inner ring there in the first place. Does the first xs650 xs1 have a exhaust that matches that outlet. Any xs1's owners out there can answer? And do you tuners out there gasflow that inner ring out? Jay

 

[5twins]

No, nothing was done on a lathe. The filler ring was just cut from a piece of pipe and it's slightly too large O.D. was then reduced with a grinder until it fit. It was pretty close so not much had to be ground off. I would like to eliminate the filler ring though, and that will require some lathe work on the insert. I want to try to thin out the flange, removing material from the inner side only, so it sticks into the head more. It seems thick enough for me to remove enough to equal the filler ring's thickness and thus eliminate it. Here's a cut-away pic of the MikesXS/Hieden Tuning AR insert. You can see how thin the flange is on it and I'd like to copy that. Also, mounted the way they have it, on top of the seal ring, results in quite a large step in the head. That step is supposed to be detrimental to flow. If I had these, I'd insert them into the head first, then place the seal ring and pipe on top of them, just like I mounted mine .....

 

[zrx1100]

No, nothing was done on a lathe. The filler ring was just cut from a piece of pipe and it's slightly too large O.D. was then reduced with a grinder until it fit. It was pretty close so not much had to be ground off. I would like to eliminate the filler ring though, and that will require some lathe work on the insert. I want to try to thin out the flange, removing material from the inner side only, so it sticks into the head more. It seems thick enough for me to remove enough to equal the filler ring's thickness and thus eliminate it. Here's a cut-away pic of the MikesXS/Hieden Tuning AR insert. You can see how thin the flange is on it and I'd like to copy that. Also, mounted the way they have it, on top of the seal ring, results in quite a large step in the head. That step is supposed to be detrimental to flow. If I had these, I'd insert them into the head first, then place the seal ring and pipe on top of them, just like I mounted mine .....

View attachment 327059

Also the seal mounted the way shown in the picture does not seal between the header and the head allowing air and exhaust to leak through. It is also clear that the insert was designed to seal against the recess in the head and the seal to be on the other side of the insert’s flange vs how it is shown