cranking compression

Discussion in 'PSI Superchargers Tech Questions' started by LEN COTTRELL, May 11, 2017.

  1. LEN COTTRELL

    LEN COTTRELL Member

    Joined:
    May 9, 2003
    Messages:
    190
    Likes Received:
    3
    I recently did a "old school" cranking compression test on my blown alcohol TAD engine. This is a standard BAE billet block with 8X heads and a crane R 296 2s r14 16x BBA 48D installed at 34 degrees BTDC with .904 lifters. The good news was that every cylinder was at 90 #s pressure. The bad news is it was only at 90 #'s.
    My notes from many years ago was that it should be in the 150# range.
    Any thoughts?
    Len
     
    #1
    LEN COTTRELL, May 11, 2017
  2. h2b puller

    h2b puller Member

    Joined:
    Feb 8, 2008
    Messages:
    73
    Likes Received:
    1
    What piston rings does it have and are they new?
    we have around 160 pounds with 56% O.D (PSI roots) with 48V rcd starter.
     
    #2
    h2b puller, May 11, 2017
  3. LEN COTTRELL

    LEN COTTRELL Member

    Joined:
    May 9, 2003
    Messages:
    190
    Likes Received:
    3
    Yes, freshly honed cylinders and new C&A rings.
     
    #3
    LEN COTTRELL, May 11, 2017
  4. Bob Meyer

    Bob Meyer Comp Eliminator

    Joined:
    May 13, 2003
    Messages:
    764
    Likes Received:
    36
    Len; been there done that........I'm a firm believer in that checking method. Some have suggested as high as 200 psi, never liked that as it's a bearing beater. 150-175 is target. On one of my downunder trips, one of my cars was running like poop, had him check, he comes back and says 50 psi. I told him his leak checker was junk, Doc Conway was there too and said use mine, it read 60 psi. I told him cam was retarded, he said can't change it, the exhaust clearance is too close now! BINGO!, that's bassakwards! Cam was 8* retarded, then got 165 psi, and boy did it come to life after he re-learned to drive it!
     
    #4
    Bob Meyer, May 11, 2017
  5. LEN COTTRELL

    LEN COTTRELL Member

    Joined:
    May 9, 2003
    Messages:
    190
    Likes Received:
    3
     
    #5
    LEN COTTRELL, May 11, 2017
  6. LEN COTTRELL

    LEN COTTRELL Member

    Joined:
    May 9, 2003
    Messages:
    190
    Likes Received:
    3
    Uncle Bob, what is your cell number?
    Len
     
    #6
    LEN COTTRELL, May 11, 2017
  7. slowpoke96z28

    slowpoke96z28 Member

    Joined:
    Jan 14, 2016
    Messages:
    39
    Likes Received:
    1
    this goes back to the old advice of always degree the cam once its in, no matter how sure of it we might be.
     
    #7
    slowpoke96z28, May 11, 2017
  8. Bob Meyer

    Bob Meyer Comp Eliminator

    Joined:
    May 13, 2003
    Messages:
    764
    Likes Received:
    36
    Ck. your PM
     
    #8
    Bob Meyer, May 12, 2017
  9. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
    Staff Member

    Joined:
    May 6, 2003
    Messages:
    6,706
    Likes Received:
    132
    Is that a 114 or 116 Lobe Separation? Also the new stiffer valve train we run these days gives the motor more duration due to less deflection. This may delay the closing of the intake valve enough to lose some cylinder pressure. This combined with whatever your static compression ratio is may contribute to the lack of cranking compression. There has been a trend of raising compression ratio as we have put better flowing heads on these cars.
     
    #9
    Will Hanna, May 15, 2017
  10. WIDEOPEN231

    WIDEOPEN231 Member

    Joined:
    Jun 10, 2011
    Messages:
    112
    Likes Received:
    18
    180 to 200 has always worked for us.Mr Ralph Gorr told me where cam should be and it should read at least 180# but less than 210#.This is with all plugs out and fresh batteries .If turning too slow it will read less. Been doing it that way for 20 years. Some time those old school ways just freaking work.
     
    #10
    WIDEOPEN231, May 22, 2017

Share This Page





XenPorta 2 PRO © Jason Axelrod from 8WAYRUN.COM