How much off the heads?

Discussion in 'Small Block Tech' started by Chuck George, Apr 9, 2024.

  1. Chuck George

    Chuck George Well-Known Member

    I asked this question a while back but can't find it now. I have bought a used set of heads. Same casting number as currently on the motor. It is the SP motor. Have read on here that this motor probably has an actual compression ratio of 9:1 - 9.25:1. I plan on having the heads I bought rebuilt and shaved a bit to bump compression. Nothing being done to the short block. Compression test done.
    #1 160 #2 155 #3 150 #4 170 #5 160 #6 170 #7 165 #8 170
    All the plugs were dry and clean. I have records from previous owners so verified mileage is 60,000.

    So my question is:
    How much should I shave off the head for a half point or so bump? Will plan on using the .040 head gasket unless someone gives a better plan. I'm thinking since not doing anything to the block I should not use the .020 head gasket.
  2. 455 Powered

    455 Powered Well-Known Member

    Go to Wallace racing calculator. They have a program for that
  3. MrSony

    MrSony Well-Known Member

    .020 gasket is worth half a point itself.
  4. Mark Demko

    Mark Demko Well-Known Member

    I’d have .030 taken off.
    My current irons I had .040 removed.
  5. 455 Powered

    455 Powered Well-Known Member

    .021-.023 using the calculator I mentioned above
  6. Mart

    Mart Gold level member

    Use the steel shim gaskets and save machining costs. I've always found the Fel-pro and GM style steel ring gaskets to mic exactly .042 compressed, not .040
    Max Damage likes this.
  7. alec296

    alec296 i need another buick

    52 cc head will net about 9.82 with a .040 gasket. I believe that’s about.025-.030 off head.
  8. knucklebusted

    knucklebusted Well-Known Member

    Are you willing to run premium gas if it pings? Depending on the cam, which you don't mention changing, it could be close to detonation range.

    If you can tell us how far the pistons are down in hole at TDC, we can better calculate your current compression ratio. More info is more precise.
    Dadrider and Max Damage like this.
  9. Chuck George

    Chuck George Well-Known Member

    Already running premium gas. Not changing the cam just having heads rebuilt and installed. Nothing fancy to the heads other than a nice valve job and a little boost in compression.
    MrSony likes this.
  10. Chuck George

    Chuck George Well-Known Member

    Thanks everyone for the responses. Have decided to install the TA DP intake as well. Already have a set of Hooker headers, bought when they were on sale last year. Getting then coated now. So I'm now looking for recommendations for gaskets. Plan on using Fel Pro. Will the stock valley pan gasket be okay? Am having .030 taken off the heads and the appropriate amount off the intake. Is the Fel Pro perma torque head gasket the way to go?
  11. Stevem

    Stevem Well-Known Member

    Ball park is .006" milled off for each CC you want to drop.
    patwhac likes this.
  12. alec296

    alec296 i need another buick

    You should not need to mill the intake. And I would mill intake side of heads . Otherwise that intake is only good for those heads . I have .025 off my heads. Ta intake fits fine. Felpro gasket. Rtv on front and rear rails. I would jet up carb with headers and intake. More air in more air out. Needs fuel. Set timing about 8 -10 initial with a distributor recurve to get the timing in sooner. I have a similar setup with a Quadrajet Power built carb. 2700 jegs small block torque converter and a ta 310 cam advanced 4 degrees. Has strong low end. Haven’t did much driving with it yet though as still getting interior and bumper work done
    Chuck George likes this.

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