Opening the headpipe ?
 

I've read about guys dremeling out the head pipe where it mounts to the engine. Anyone have any before and after pics? Is it worth doing? Or is it a mod about like removing the backfire screen.

When I replaced my stock piece with an aftermarket one I saw a small but noticable improvment. I'm not sure just porting the end where could get to it with a dremel would do alot though.

So you installed and new header and it only made a small difference? Was it not worth the $$? Do you recall if the diameter inside the pipes are much different?
IIRC - the 250 and 300 headers are the same.

don't do it! you'll blow a muffler bearing. ;-P

My aftermarket piece was a powerbomb, and yes the ID was greater than the stock piece it replaced. And it did make a small improvment, not nearly as much as the powercore 4 that I had already added.

As far as being worth it, I was and am trying to wring as much power out of the stock 250 as possible and from that stand point it was worth it. I will soon go to a 351 and I'm sure anything I gained will show up there as well.

^ have you considered matching the exhaust port to the header, is it plausible? Im throwin the q4 and powerbomb on when i get my tax returns.

just asking because in my fluids class a stepped outlet has a significant loss factor on fluid flow, the klx head and powerbomb would be similiar to a stepped outlet... turbulence vorteces around corner of the larger diamter.