125 expansion chamber dimensions

[kiwi86]

I'm doing a bit of research into modifying my expansion chamber for a little more bottom end. To get a bit more info on what I am working with I am after the following;

Dimensions for a stock 02 YZ125 pipe, all internal dimensions, ie header length/diametre/taper, diffuser/baffle cone taper, stinger length and diametre etc

Also, I am after power valve positions at X revs; what revs should it ideally begin to open and at what revs should it be fully open.

Any help appreciated,

Thanks

[SellYour4Stroke]

Yeah those yzs don't have much in the way of bottom end, do they.  Milling the head might be a little easier than pipe mods to try to get a little grunt out of them. I've had a lot of good feedback on head milling mods. People seem to like them. 

[kiwi86]

Yeah those yzs don't have much in the way of bottom end, do they.  Milling the head might be a little easier than pipe mods to try to get a little grunt out of them. I've had a lot of good feedback on head milling mods. People seem to like them.

I have considered this, have you ever done it yourself? Or been able to ride a bike before and after milling the head to compare just how much difference it makes?

[SellYour4Stroke]

I have considered this, have you ever done it yourself? Or been able to ride a bike before and after milling the head to compare just how much difference it makes?

Ive milled .025 off my own yz head and it added some noticeable snap. Also put many milled heads on other bikes and swapped dome sizes on others.  I havent done enough research to give a real definitive number as to how much to mill, though. TT may have some articles on it.

[kiwi86]

Thanks for the feed back Jeff.

I measured my squish band recently, it is at .9mm, so I should have plenty of meat to take off, might check out you tube to have a look at the process for milling a head. I have also heard of milling a little off the bottom of the jug for a similar effect, with the addition of lowering the port height.

Any idea of the ideal position for the power valve at X rpm? Particularly, what rpm should it fully open?

I still haven't ruled out the pipe mods, the reason I am so keen on this is I ride in really various terrain, I want 2 pipes, one stock and one modded or better still, custom made, for a much lower power curve. That way I can change the power delivery to suit where I am riding with a quick pipe change, and re-jet if needed.

[UncleLuke]

I want 2 pipes, one stock and one modded or better still, custom made, for a much lower power curve. That way I can change the power delivery to suit where I am riding with a quick pipe change, and re-jet if needed.

 

They make it already, the FMF Gnarly

[kiwi86]

They make it already, the FMF Gnarly

the gnarly was only made for 250's, as far as I know.