Need educated guesses

Discussion in 'High Performance Modifications' started by biker, Oct 5, 2017.

  1. biker

    biker Veteran Member

    Looking for estimates as to what my cranking compression test readings should be.

    Calculated SCR is 10.01:1. Engine is small block 383. Cam is hydraulic roller .530/.545 lift, duration @.050 is 233/241 lobe separation is 110 degrees. 1.5 rocker arms. Performer RPM intake, 195 runner ATK heads with 2.02 intake valve. Quadrajet held wide open while cranking, engine warm.

    Considering the cam timing, intake and heads, I'm thinking there is not a great deal of intake velocity at cranking speed, especially with gear reduction starter.

    Closest guess wins the prize. Thanks guys.

  2. Bandit723

    Bandit723 Veteran Member

    Oct 1, 2016
    Waupaca WI
    I'm in 180 to 190....
  3. tom3

    tom3 Veteran Member

    Aug 1, 1999
    Quite a bit of duration @ 110 degrees on a small block, but extra cubes there too. I'm a bit lower, 175 give or take 2 psi. Chicken Dinner?
  4. G72Zed

    G72Zed Veteran Member

    Sep 8, 2015
    What type of rings, specs ?
  5. biker

    biker Veteran Member

    Speed Pro hypereutectic pistons that came as part of my Eagle stroker kit with forged crank. Rings are 2.0mm, 1.5mm, 4.0mm.
  6. jimrr

    jimrr Veteran Member

    Jun 12, 2016
  7. biker

    biker Veteran Member

    Well, Bandit is right in the ballpark, but Tom nailed it. 177 by my guage. I was asking because I see guys posting some high readings, but those must be some tamer camshafts. I've been applying some tame cam logic to my tuning, but as Tom said, pretty long duration to expect great idle manners. Idle seems happiest at about 1000, but I am a bit lean on idle mixtures despite opening up the QJet idle circuits.

    Thanks guys, good to know my cranking pressure is about where it should be.

    Tom, if you find yourself in Northern Ontario, chicken dinner is on me.

  8. biker

    biker Veteran Member

    Great. A science geek.
  9. G72Zed

    G72Zed Veteran Member

    Sep 8, 2015
    I say around 185, and +12-15 psi more if it was a 2 piece total seal top ring.
  10. 77 cruiser

    77 cruiser Veteran Member

    Nov 17, 2006
    Frostbite Falls MN
    How much vac. at idle?​

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