55mm cam and .904 or .937 lifters - Is it worth it?

Discussion in 'PSI Superchargers Tech Questions' started by Critical Mass, Oct 4, 2011.

  1. Critical Mass

    Critical Mass Member

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    I broke my BBC Big-M block; #7 and #8 rods left after 57 passes on the rods. I am now pursuing a new block with same setup; 10.2 deck and 4.600 bore with billet caps. My question is should I go to a 50mm or 55mm cam and larger diameter lifters?

    Thanks in advance for any advice, Joe
     
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  2. WANNABE

    WANNABE New Member

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    I have not seen too much advantage for larger cam cores. I have seen lots of help with roller cam bearings, (but that is naturally aspirated where I can see small differences.)
    The change from a standard to .904 lifters is over 100% longer life in the lifters. And we have seen as much as 200+% in large spring pressure BBC's. And the keyway deal is even more yet.
     
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  3. jay70cuda

    jay70cuda Active Member

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    I think it really depends on how hard you rev it. My 525 chevy has 55 mm and .937 keyed lifters . It seen 10000 rpms constantly and never seen a issue. However if I had a chance to do it again I would do 65mm cam and 1inch lifters with no offset even it it requires moving the lobes so the geometry is correct. Hope it helps
     
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  4. WANNABE

    WANNABE New Member

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    Jay, I am with you. But he is talking about a standard Big M iron block. Those things don't take too well with huge lifter bore holes, and inserting bronze 1 inch lifter sleeves then taking alot of the meat out of the cam journal.
    If you are running 10K every pass on a standard lifter, you are asking to saw a block in half.:cool:
     
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  5. Comax Racing

    Comax Racing Member

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    What rods were you using?
     
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  6. Critical Mass

    Critical Mass Member

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    I'm using heavy Venola aluminum rods and pistons. The motor runs around 7800 rpm with 20# of boost.
    Thanks guys for the input.
     
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  7. Comax Racing

    Comax Racing Member

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    The reason I ask is that is a fairly low RPM and boost level. 57 passes is not that many, any theories as to why the rods decided to make a quick exit?
     
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  8. overkill69

    overkill69 Member

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    904

    Big lifters are a nice deal but at your HP and boost about anything should live. I've always run the stock core cam and it's hard on cam bearings but has worked ok to 9000rpm.
     
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  9. Critical Mass

    Critical Mass Member

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    Yes, in the beginning of tuning, I detonated the motor with too much advance, 37 deg. I'm using a 44 mag and I have been told with that mag the motor behaves like it has more advance in it than it really has? I believe detonation weakened the rods?
    Thanks, Joe
     
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  10. WANNABE

    WANNABE New Member

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    Well, it should be real easy, if it was the detonation, the bearings should show it real well.
    Also, did the bearings cause the rods to break, or did they just come apart?
     
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  11. Critical Mass

    Critical Mass Member

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    WANNABE you are right; however, I replaced the bearings after the detonation. It's any ones guess on the rods. I boxed up all the debris and the rest of the rods and sent the scrap to Venola. I haven't heard a word yet; just a credit card bill.

    Thanks for post, Joe
     
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