need advice on sorting out my cylinder head on my 05 250

[rvktm]

thinking of sorting out the head volume/ piston clearance .piston level at bdc for a long time .then a modified head and alloy barrel spacer came my way for not much money .the question i have is by lifting the barrel to make the piston level with lower edge of the ex port at bdc .how will it change the power

 

[(F5)]

Gah! The bottom of the port is not the crucial point. It's the top. However they are of course on the same barrel so raising one raises the other and the transfers. Rule of thumb is higher exhaust will be more top end with trade off at bottom. I've only played with gaskets on 200 and 300, so cant give experience.

As far as the head mods go, it depends how much you trust the person who did it and how close in tolerance your bike it to theirs plus what gas you will run. Read my thread on 300 head mod. Principle is the same and will clue you up what simple measurements will keep you safe and get most of the advantages on offer.

It's a bit rambly but gets there.
http://www.gasgasrider.org/forum/showthread.php?t=16560&highlight=Head

 

[rvktm]

thanks f5 did think that .not looking for top end power .so if the piston is above the ex port at bdc its not big deal the piston to head and shape and volume of the head are.had my 05 from new came with a reed spacer the boysen rv didnt fit with out the spacer so i used one of 98 .the best thing i had on the 05 was a adjustable pv cover made the 250 .fitted it to the 13 300 that got stolen

 

[(F5)]

My 300 came with 2 base gasket so it only wears 1 now.