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DCR help please

Discussion in 'Street/strip 400/430/455' started by 67Skybird, May 9, 2025 at 2:49 PM.

  1. 67Skybird

    67Skybird Josh - Minnesota

    Hello,

    I think I am using the DCR calculator that Larry posted incorrectly. I come up with 9.245. When I put in the specs Larry referenced "I run 10.5:1 with a 230/238/112 cam and a DCR of 7.8 in my current engine." the calculator comes up over 9.0.

    My combo:
    1971 455 bored .007 to 4.32
    stage 2 SE heads 63.5 cc
    pistons ordered from JW 4.320 bore 1" pin 4.995 comp dist. 26cc dish 1/16 comp 3/16 oil ring (these have 2 valve notches, not sure if that adds to cc, notches not noted on order.)
    0.00 deck
    TA orange head gasket advertised as 10 cc
    roller cam from TA: intake 228 exhaust 245 IO 0 btdc, IC 48 abdc, eo 56.5 bbdc, ec 8.5 atdc, overlap 8.5, lobe seperation 114 roller rockers 1.6 lift .560,.560.

    please let me know what you come up with.

    Thanks,

    Josh
     
  2. 67Skybird

    67Skybird Josh - Minnesota

    Cam card for reference 20250509_173555.jpg
     
  3. knucklebusted

    knucklebusted Well-Known Member

    I calculate you are running right at 10.39:1 compression ratio with the information you've provided. The uncertainty of the valve reliefs may lower the CR slightly.

    With the cam you list, installed as indicated, you have a dynamic stroke of 3.07" and a DCR of 8.39:1.

    If you installed the cam 4° advanced, you would have a DCR of 8.64:1 and dynamic stroke of 3.17" in my calculations.
     
  4. 87GN_70GS

    87GN_70GS Well-Known Member

    You will need to used advertised valve event numbers instead of 0.050"
     
  5. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    This is what I get with your numbers,
    67SkySCR.JPG
    67SkyCamTiming.JPG
    67SkyDSL.JPG
    67SkyDCR.JPG
    If you run that cam 4* advanced, 110ICL, the DCR comes up to 7.46.

    Edit, TA Orange Crush gasket at .038" That raises SCR to 10.47:1, DCR to 7.21 (114ICL), 7.51 (110ICL)
     
    Last edited: May 10, 2025 at 7:22 AM
  6. Stevem

    Stevem Well-Known Member

    I would use a number of 4 CCs for the 2 valve notches.
     
  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    26cc covers the dish and notches.
     
  8. 67Skybird

    67Skybird Josh - Minnesota

    Thank you all.
    I was using the .050 numbers instead of the advertised. I feel much better. This should run on pump fuel.
    I look forward to getting it together and on the dyno later this summer. Still need roller rockers and headers.

    Josh
     

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