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  1. #1

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    stock 951 head milling? how much?

    does anyone know how much to mill off a stock head to give you the 15 psi gain in comp that ben mentioned? i dont have the cash for a race head but have one from race 24x that i can do some work to. thanks again!


  2. #2
    race24x's Avatar
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    Yeah but he cant be faster than me so dont tell him LMAO

  3. #3
    race24x's Avatar
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    Hopefully we can find this cause my buddy at the machine shop said put some thing (not sure what he called it and put the plug in fill it with a liquid and measuer it with a aww crap I dont remember but thats just to get a base measurement. Then cut it down measure it again, and he said its possible one side different from other so both should be measured and if different use a average of both or cut some out of the dome. Anyway it gets expensive someone must know.

  4. #4
    96 xp stroked, coffmans pipe, r&d 61.8mph gps! merfturtle's Avatar
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    To get a base measurement bring the piston to TDC and fill the combustion chamber from a beret which is a precisely incremented vessel. This will give you the volume of the combustion chamber. take the volume of the combustion chamber and calculate your compression . Now calculate how many ccs it will take to get to your desired compression. Then calculate how much material to remove from your head to reach the ccs you calculated to get to your desired compression. Are you starting to see why this is so expensive????

  5. #5
    PEST!'s Avatar
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    If you just shave the head your going to ruin the top end you need to have a 2 stroke specialist cut the head. PPG did my last head for less than $100 . IF you cant afford to do it right you just cant afford to mess with it.. Burn a pistonand you cant ride for how long? Not a wise thing to mess with something that aint broke on a tight budget

  6. #6
    these are tuned by squish... you can buy different thickness base gaskets to acheive a similair effect, however get the squish wrong and you'll be running strange if at all... Leave it alone if you ask me.. Or buy a miller head with the right squish already machined in...

  7. #7
    96 xp stroked, coffmans pipe, r&d 61.8mph gps! merfturtle's Avatar
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    Quote Originally Posted by spinyard View Post
    these are tuned by squish... you can buy different thickness base gaskets to acheive a similair effect, however get the squish wrong and you'll be running strange if at all... Leave it alone if you ask me.. Or buy a miller head with the right squish already machined in...

    Due to small differences in castings, proper squish can't be built into an aftermarket head. thats the purpose of the different thickness base gaskets. Squish gap must be checked for a stock or aftermarket head during a rebuild.

  8. #8

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    i dont get it pest says you need a specialist to cut the head? your just planning it to take of metal right? the question is how much to take off thats where it gets tricky,having someone do it that knows! i just read my shop manual and of the different base gaskets there are there is only 4 thou. diff between them so if my mach. runs good on reg gas what would it hurt going down one size on the base?it will have the same effect as milling the head right,just bring the comp up a little bit?

  9. #9

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    No, you are NOT just planing the head down to achieve lower head volume (higher compression). 2 seperate cuts must be made to the head. One is planing the head, the other is recutting the squish clearance and/or changing the squish angle. Both cuts MUST be made to get the correct compression/squish without detonating. This is not a job for a machinist without Rotax tuning experience. There are several well known Rotax tuners around that cut heads and (surprizingly) they all use a slightly different combination of cuts to achieve increased performance. Some tuners are more successful than others.
    Robert V

  10. #10

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    "i just read my shop manual and of the different base gaskets there are there is only 4 thou. diff between them so if my mach. runs good on reg gas what would it hurt going down one size on the base?it will have the same effect as milling the head right,just bring the comp up a little bit?"

    yes some people do this so they don't have to always take apart their engines. Just take your time...... But first measure your CURRENT squish....

    TLR

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