cr125 exhaust port (2000 model)

[angst2]

I have my head off for a ring job and will also be installing a v force on my 2000 cr125.
The previous owner did not polish the intake ports like I had thought. I was going to try to high grit sand and polish these since I had the bike apart already.
My question is, when you look in the exhaust you can see that the exhaust port is oval before it meets the round bolt on part that the exhaust pipe attaches to. There is a section on the top that looks like it cuts off several millimeters of potential opening for exhaust gas to flow out of. Folks around here have advised me that if I grind that out to match the diameter of the round exhaust that there are no potential negatives to bottom end power and perhaps an increase in top end power.
Any reason that I should or should not consider doing this?
This seems like if would open things up considerably but it is also changing the shape several millimeters from what honda intended. Is that exhaust port that shape for a reason?

 

[marcusgunby]

I did it to my 02-not sure if it made much difference.It should trade bottom for top.Most bikes have this kind of shape to the exhust manifold.I would leave it alone.

 

[ERICLONEY]

the exhuast manifiold on the 01 cr125 has the oval shape your talking
about and it will bolt on your 2000. as far polishing the intake goes
the intake should be left unpolished as that helps atomize the fuel as
it goes thru the intake. if you had a cylinder done by pro-circuit or
any other hop up shop you see that they polish the exhuast but leave
the intake unpolished.

 

[Zenith]

angst2 - I think if you do a search in the old Tech Articles forum you willl find a thread about Rich Rohrich where Eric describes the purpose of that little over hang and how himself or/and Rich invented/discovered it...

Found it! http://www.dirtrider.net/forums3/showthread.php?s=&threadid=40126&highlight=Rich+Rohrich

12) First use of an insert in the head pipe to enable an additional reflection point for the compression wave in the mid-rpm range. Now its routine for manufacturers to include this idea into the exhaust manifolds.

Ok so it doesn't explain it's full purpose but there are it's origins anyway[:)], I'm sure Eric or Rich could comment on it.

BTW. Eric didn't grind it off when he ported my 00CR125