topend question about compression

[duneracerweston]

Ok so as some of you know I race mx in the 350class and so dose quadaddict and were were discussing comression with each other and what we want to know how much yyou would have to mill the head to bump the compression from 10.5:1 to 11.5:1 I know you can do it on the old 2 strokes but I wasn't sure if its possible on a warrior head sice his head is pulled apart right now it would be the perfect time to mill it

Any help is appreciated
Weston

 

[dirtrider73068]

Well I would think you would need to measure the drop in the valves when they are compressed into the cylinder to make sure they don't hit the piston when it comes up. I would think to if the piston is it full up stroke and is the top if the cylinder it wouldn't reach the valves. You might find one that has been milled and see how to measure the height of the head on a flat surface and see how much would need to come off. This is just a guess. Or measure the amount of combustion chamber?

 

[elwood]

I think you better off getting a 12 to 1 piston and a thinker head gasket, then the piston has the needed vavle releif. 2stroke you can shave cause there is no valves to hit the piston

 

[beastlywarrior228]

youd need to find the volume of the chamber first

 

[WrenchWarrior903]

one more problem yall mite be overlooking. how much can you mill before the timing is off or tensioner is out? probably not a issue with a adjustable timing gear, but if its milled too far it should be off some? just a head scratcher,i was looking at doing this too while apart,but oh well

 

[duneracerweston]

Well its going to be in the hundreths so it won't b off much I was hoping some one already knew all the specs and stuff so all I would have to do is mill it but it seams like this is new to every one but one more idea would it be easyer to buy a 12:1 and shave the piston to lower compresion?

 

[jasonp]

Yeah the valve timing will change so you will have to adjust it back into time with adjustable gear. Had to do this with mine.

You really don't need to mill the head down. Just use gaskets, base and head to get you there. What you are really looking for is .040" of deck clearance between the top of piston to the head (top of the head gasket).

The stock gaskets are really thick and since most piston manufactures use this as a guide to set there compression ratio on the performance pistons you can use this to your advantage. Really reducing the CC in the head is something I would do if I couldn't achive what I wanted to do in gasket thinkness.

Cometic will make what ever thinkness you need to get your deck clearance right, while still being cheap. Also JE will make a custom piston if you want.

If you really want start talking with Mickey Dunlap or Loran Duncan and they will be able to help.