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 .....

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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.