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How much to mill head to raise compression by .6?

Discussion in 'Engine Building' started by BigBoy, Nov 23, 2005.

  1. BigBoy

    BigBoy Senior Member

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    current setup:

    jdm b16a
    1 layer oem gasket
    11:1 comp

    Im gonna do a port and polish and while i have the head off I want to raise compression a little more. But im gonna go back to the stock 3 layer gasket which will put me at 10.4 stock compression.

    My question is how much do I need to mill the head to get it up to 11:1?

    After the milling, im gonna throw in some high comp vavlves to give it a .3-.5 bump. Final compression will be 11.3-11.5ish
     
  2. hcivic.com

    hcivic.com Senior Member

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    with high comp pistions, a milled head and high comp valves, you may have a problem
     
  3. BigBoy

    BigBoy Senior Member

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    as far as piston valve clearance?
     
  4. kyleirwin

    kyleirwin Retired OG

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    yes, that's what he's saying, but you should be alright. always clay the enigne to be sure though.
     
  5. jlicrx

    jlicrx Senior Member

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    just mill the head for the difference in thickness of the 2 gaskets - won't change clearance from what you have now
     
  6. BigBoy

    BigBoy Senior Member

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    cool...so will high comp valves really raise it .3-.5?

    Also...can i go higher than 11.5 on 91 pump gas?
     
  7. BigBoy

    BigBoy Senior Member

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    im gonna stay all motor...but im thinking of milling 0.030 which will give me a compression of 11.4. Will i have a problem running skunk2 stage2 cams?
     
  8. Taco15

    Taco15 I wear stretchy pants VIP

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    i'm running 11.3.1 comp. with skunk2 stage2 cams,retainer and springs. havent had a problem. ohh and the block is .020 over
     
  9. pissedoffsol

    pissedoffsol RETIRED

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    bore is not head mill.

    IMO, shaving the head is the wrong way to gain compression. it should be used to level the head only.

    if you want to bump your b16 up, score some jdm ctr pistons and eagle rods. that will give you about .7 raise in cmpression. the c-speed calc is wrong. it shows a .4 raise... but it doesn't take into consideration that the pct piston sits ABOVE the deck heigh of the block. The pct's are taller by about .03'' so there's your "mill" job right there....

    with a b16 block and head, you're looking at:
    81mm bore: 11.64
    81.25 std overbore: = 11.70

    those figure assume an OEM 3 layer gasket @ .026

    if you're thinner, you got even more compression.

    [​IMG]



    BUT, IMO, going for these numbers compression (with your 1-layer gasket, you're over 12 for sure...) you're going to end up pulling timing to comp for the shit 91 octane gas... especially with the higher duration cams.

    its a great build. but the stupid republic of cali won't let you enjoy cars and get good fuel....

    i digress...

    another thing to consider, is that when you change headgasket thickness, it requires a lot of cam timing to adjust, as the cam comes on "earlier" due to the height... which can lead to hours fo headacheson the dyno when yuo're putting out 140 whp on you're built b16...
     
  10. BigBoy

    BigBoy Senior Member

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    cool thanks for all the info. So if i pick up some ctr pistons and a mugen headgasket...what will my approx comp be and will i have to worry about valve/piston contact? do i have to clay the motor?
     
  11. pissedoffsol

    pissedoffsol RETIRED

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    you should ALWAYS clay the motor. it doesn't take too long, and it could save you a shit load of money and time. i don't know how thick the mugen gasket is, so i can' say...
     
  12. jkeg6

    jkeg6 New Member

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    Saw your #'s on another post. Congrats! I was wondering how that single layer gasket was holding up. I'm also running a jdm b16 & getting ready to install an itr head with ctr cams. I figured that since the head was going to be off, why not raise the compression a bit. I'm shooting for 11.1:1 & don't want to mil the head, but do want to stick with the P30 pistons instead of the PCT ones due to less work & the P30's are the lightest b series pistons from what I understand. Also which layer did you use? I've heard everything from top & bottom layers are best to middle & top/bottom to just middle since it's the thicker of the three. Would a copper sprayed single layer be reliable? Not trying to get an crazy hp/tq #'s, just a fun reliable smooth running daily & really not trying to be replacing head gaskets every 40K!
     
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