I just picked up a 2004 TYS125F. The bike is in great nick overall, but the header pipe is pretty rusty from sitting outside. I'd like to replace it with a titanium aftermarket pipe. There are several choices in Japan where I am. One has a bigger diameter overall and a small expansion chamber. The other seems to be a similar diameter to the stock header with a small expansion chamber. Any recommendations on which would have the most suitable power characteristics for this small motor? The use is slow speed cross-training and trail riding. Some road riding as well to connect trails. Cheers.

find someone to glass bead blast your stock pipe then go over it with scotchbrite. those expansion chambers may be cat converters!

No cats for sure, they claim they increase performance. 

 

Hello S10, I've ridden a load of these over the years some with aftermarket pipes and modified silencers.

I really never noticed any difference other than some are bit louder.

You can't really clean the original up as it'll rust quickly so a nice shiny new one would be a good idea.

If you want more power better get a big bore kit say a 163 ,but I would just keep it stock unless you're planning on a competing.

Have fun, they're great bikes.

4 hours ago, breagh said:

Hello S10, I've ridden a load of these over the years some with aftermarket pipes and modified silencers.

I really never noticed any difference other than some are bit louder.

You can't really clean the original up as it'll rust quickly so a nice shiny new one would be a good idea.

If you want more power better get a big bore kit say a 163 ,but I would just keep it stock unless you're planning on a competing.

Have fun, they're great bikes.

Thanks for the feedback. What I'm also wondering is whether the larger diameter of the two will have a negative impact on lower end torque. No plans to change the stock silencer, it's pretty loud as is.