heys guys, i have yet another question. i am guessing this is the right section.

i am building a usdm motor for boost. i've had the block and head at a machine shop and just got it back.....so now i am ordering parts left and right. i ordered 8.5:1 pistons. i am going to use the cometic head gasket. now i know you can use a thicker or thinner HG to mess with the comp ratio. i was going to keep it at 8.5:1 maybe drop it to 8.3:1. only thing is i noticed on my bill it says they surfaced the head. it read this exactly: "surface heads-inline 4 cyl to .020."

so here is my question.....how much will .020 effect my comp ratio? what thickness HG should i use with a .020 gone to keep it at 8.5:1?
i know how you guys are, and understand you want me to find my own answer so maybe if ya'll just gave me the equation i can fingure it out. i am not looking for the answer, just how do i go about finding the answer....besides SEARCH cause i did and found nothing on this.

thanx a bunch!!!!!
~leon

or maybe i am misunderstanding my bill all together and am just dumb.......
i dont know, i learn as i go....and this is uncharted territory:D

ok, so i did some more searching with different search words and found a wee bit more info.

not my answer though. i am looking for a formula to calculate comp ratio between pistons, head gasket, and a machined head. thanx again...am i making sence?

I would not use a resurfaced head because it will not only mess with your compression but also your timing, same thing with a thicker or thinner HG. I cant remember but isnt 20 thousandths a lot to shave off the head?

i dont know, thats why i am asking:dunno:

aww gees, dont tell me i gotta kick some machine shop ass.

i dont know, that why i am asking:dunno:

aww gees

all I can remember is someone (who I think was knowledgable about such things) posted up to not use a head that had been machined .016 because it was too much, but I could be completly wrong.

http://www.sr20forum.com/showthread.php?t=96120&highlight=block+thousanths

in this thread Travis mentions that .020 off the head will cause a drastic change in compression ratio.

but he is refering to a qr motor......yes i see the drasticness, but still, different motor.