top end mods

[Justin Terry]

Im going to be modifing my 05 yz 125 top end. I am a machinist by trade so I will be doing it all and the porting. I port alot of intake manafolds and cylinder heads for race cars where I work. But I have a couple of questions on what to do.

I ride mx and the class is ride is 125-B, I dont wanna do the big bore yet. So Im stuck with either cutting the head or cylinder. I know cutting the cylinder will retard port timing and give more low to mid, but I dont really want any more low I just want more mid to top. So would be cutting the head and cylinder both alittle bit. And porting or what should I do.
Also on the porting when im porting it. Where should metal be removed and how much. If anyone has pics I would appriciate it. Or someone could measure there ports and let me know about what they are. Thanks

 

[Justin Terry]

I posted this in the Eric Gorr forum how did it end up in here?

 

[motometal]

I appreciate your mechanical/machinist abilities. Porting is a real science. If you really want to learn about it, start with a search...not just on this website but using a general search engine.

Regarding your question about removing material from the face of the cylinder and/or head, I believe this could help your overall power and decrease chances of detonation by providing proper squish clearance, assuming clearance is currently greater than ideal and the machine work was done properly. However, the downside is that as you increase compression you will actually reduce high rpm power, particularly if the proper other porting modifications aren't done at the same time. Many times the are inside the squish band is machined a bit to bring the compression back proper. Also, if you make squish clearance too tight you will crash the engine. Really, I am oversimplifying here and again I think you will find a world of knowldege by searching.