Static Compression to Octane

Mopar Performance Issues

  1. josekh7

    josekh7 Well-Known Member

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    Hi Guys i just finished my BB440 and i am about to break it in. I used edelbrock 84cc heads flat piston with 2 valve reliefs which brought me up to 10.23 compression. Can i use 91 octane or whats the safety area on octane gas i can use?
     
  2. Phreakish

    Phreakish Well-Known Member

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    Not enough info. You'll need to list cam specs. Duration @.050, lobe separation and installed centerline.

    Otherwise start with high octane and work down until it grenades - then build the next one and always use more than what kills this one ;)
     
  3. mguner

    mguner How many is too many?

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    Aluminum heads should let you get by with 91. A short duration cam or low overlap profile could make it a little dicey.
     
  4. josekh7

    josekh7 Well-Known Member

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    RPM-Range: 2500-6800 Value Lift Int/Ext: .485/.485 Value Lash Hot Int/Ext: .000/.000 ADV Duration Int/Ext: 280/280 .050 Duration Int/Ext: 232/232 Lobe Center: 108

    Isky 280 mega hydrolic
     
  5. MoparLeo

    MoparLeo NRA PATRON LEVEL LIFE MEMBER

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    Is the CR calculated or measured ? What was the formula used to calculate the CR.
     
  6. josekh7

    josekh7 Well-Known Member

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    calculated that's what my engine builder gave me
     
  7. Dubob

    Dubob Well-Known Member

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    My build 440 lunatti solid roller 237/243@.050 .566/.577 lift. Eddy 84cc static 9.9-1. MRL recoommended 89 and up. I would contact your builder and ask them what they recommend. Safest way to go in my opinion.
     
  8. MoparLeo

    MoparLeo NRA PATRON LEVEL LIFE MEMBER

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    Ask your builder for the measured specs he used ( combustion chamber volume, volume of the area from the top of the piston, If the deck is above the piston top, Gasket volume and the formula to calculate his answer. It will be good info in the future for any other project you may want to build and will help you in your parts choices.
    Here is a posting by Krazycuda a few years back.
    http://www.forabodiesonly.com/mopar/showthread.php?t=278215
     
  9. Lustle

    Lustle Well-Known Member

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    Another note here is don't forget altitude and timing. They have an affect on what compression you can run.
     
  10. josekh7

    josekh7 Well-Known Member

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    so start at 91 or 93 to be safe and go down from that?
     
  11. EL5DEMON340

    EL5DEMON340 Well-Known Member

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    I run 11.25cr on 93. It all depends
     
  12. josekh7

    josekh7 Well-Known Member

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    how would you listen to pinging or detonation?
     
  13. Phreakish

    Phreakish Well-Known Member

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    Way to muddy things with irrelevant specs. Cam, chamber design, quench, it all matters. 11.25:1 on 93 isn't even half the conversation.
     
  14. TrailBeast

    TrailBeast Slightly Twisted Member

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    With your ears. :D

    My smartass gets loose sometimes.
     
  15. Phreakish

    Phreakish Well-Known Member

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    Sounds like marbles in a glass jar - nasty.

    Keep the timing low, start with 93. Check spark plugs as you go. Detonation/pinging will leave little specs of aluminum (piston) on things. Sometimes.

    Based on your questions and concerns I'd contact your engine builder and have some conversations regarding what you should do and how he can help.

    Early tuning on a new engine can be tough and inexperience can lead to costly mistakes in a hurry. Higher compression tends to be less forgiving of timing mistakes and the like.
     
  16. moper

    moper FABO Gold Member FABO Gold Member

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    I would run 93 and I don't think you'll have a problem but a lot of no detonation is about your tuneup. So - listen for pining, and check the plugs with a lit magnifier for signs of aluminum transfer.
     
  17. oldkimmer

    oldkimmer FABO Gold Member FABO Gold Member

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    ........I always build the engine to my fuel choice, not the other way around, as many ppl don't want to buy the more expensive fuels...........kim........
     
  18. moper

    moper FABO Gold Member FABO Gold Member

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    That is the best way, yes...lol
     
  19. RustyRatRod

    RustyRatRod 30 Degrees Outta Whack FABO Gold Member

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    That thing will probably run on 87.
     
  20. EL5DEMON340

    EL5DEMON340 Well-Known Member

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    Ok here you go, cam is 520/540 lift on 110lsa, 244/252 @.050. Chamber is a "J" head, heat crossover blocked, no quench, no sharp spots on Pistons/heads, polished exhaust port, VERY cold plugs, 14 initial 30 total all MSD, 10w30 oil flowing faster to pull heat out, I'll even add a bit more, thermo coated headers, J54 hood which allows a little cold air under the hood, elec fuel pump, 4 row radiator without trans cooler, sealed and air dams to direct airflow to radiator, 4,400 stall with stand alone cooler, 3,450lbs demon with driver, runs and sounds great !! Oh 195psi cranking.
     
  21. Phreakish

    Phreakish Well-Known Member

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    Perfect! Now we can see how you get away with it ;)
     
  22. RustyRatRod

    RustyRatRod 30 Degrees Outta Whack FABO Gold Member

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    It's not like it's ever been a secret. He's shared his build a hundred times I bet. Probably the best pump gas build on here, IMO.
     
  23. EL5DEMON340

    EL5DEMON340 Well-Known Member

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    Thanks RRR, it's not bad for mostly junk parts.
     
    • Like Like x 1
    • AJ/FormS

      AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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      Like Rusty said, it'll probly run on the crappiest gas you can find, unless you put in a cement truck with hiway gears, with a rotten tune.
      Well he didn't actually use those words, I'm paraphrasing.
       
    • mopar373

      mopar373 FABO Gold Member FABO Gold Member

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      11.78cr Lunati 292/512H, eddy heads, 36* total, 93 octane, 340 .040 over w/360 truck crank, 3yrs no problems. Like MRL said, it all depends on the combo!
       
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