Increase in displacement and effect on maintenance

Discussion in 'PSI Superchargers Tech Questions' started by NRG, Oct 20, 2009.

  1. NRG

    NRG New Member

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    I currently run a 285 cu in. V6 GM block with 4.04 in. diameter pistons and 3.625 in. stroke with a 5-71 high helix running at 20psi. In order to keep up with the competition while maintaining the underdog status, I have considered in increasing the bore from 4.04 to 4.5 in. diameter pistons making it roughly 345 cu in. While maintaining 20psi will this change create more maintenance for the rods, bearings, crank, etc?
     
    #1
    NRG, Oct 20, 2009
  2. blown375

    blown375 New Member

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    what about increasing the size of the blower so you can make more boost at less overdrive ?
     
    #2
    blown375, Oct 20, 2009
  3. NRG

    NRG New Member

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    Will this change in displacement @ 20psi create more maintenance on the crank, rods, etc, without increasing blower size?
     
    #3
    NRG, Oct 20, 2009
  4. aj481x

    aj481x Member

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    A 4.5" Chevy V6 with a 5-71 ???
     
    #4
    aj481x, Oct 21, 2009
  5. Moparious Crewcheif

    Moparious Crewcheif New Member

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    Simple math. More power=more maintenance
     
    #5
    Moparious Crewcheif, Oct 21, 2009
  6. JustinatAce

    JustinatAce Member

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    Yes. when you increase displacement, you have to fill the holes. It usually creates a nice situation where your pistons get heavier from an increase in Bore size, which is harder on rods, mains, bearings and cranks.
     
    #6
    JustinatAce, Oct 21, 2009
  7. Money Shot

    Money Shot Member

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    4.5 bore

    Can you put a 4.5 bore in a v6 chevy? What block are you using?
     
    #7
    Money Shot, Oct 21, 2009
  8. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    blower

    one thing to consider is when you have a blower, your cid is bolted to the intake. boost per cid is more important than cid. granted this is on a relative scale. sure a 526 is going to make more power than your 302, but i don't think you'll see quite as much out of 60 cid as you would turning the blower up. not to mention it will be a hell of a lot easier.

    granted if you do both, you'll go faster.

    to answer your original question, i'll tell you like norm grimes told me once. "Any time you make more power, you have to pay the tax man somewhere."
     
    #8
    Will Hanna, Oct 21, 2009
  9. NRG

    NRG New Member

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    It's a 4.3 bowtie block.
     
    #9
    NRG, Oct 21, 2009
  10. NRG

    NRG New Member

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    I'm considering an increase in bore from 4.04 to 4.25. Left out the two.
     
    #10
    NRG, Oct 21, 2009
  11. JustinatAce

    JustinatAce Member

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    Another thing to think about is that without putting more into the blower, changing the stroke, rods, cam and/or piston style you won't maintain 20psi because you will be filling a larger volume on the intake stroke.

    As Will said, it would be a helluva lot easier, and cheaper to change a couple pulleys and turn up the blower.
     
    #11
    JustinatAce, Oct 21, 2009
  12. Bottlefed

    Bottlefed New to Blowers

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    Another big issue that I do not have the answer to will be cylinder distortion, even though the common take on the block from NA or Nitrous guys may be it will stand the overbore you will never find out if the cylinders will stay round until you do it with boost. IMHO even though the peak pressure with nitrous may be as high or higher the low rpm midstroke cylinder pressures will be greater in a roots blown situation.

    Richard G
     
    #12
    Bottlefed, Oct 22, 2009
  13. secondwindracing

    secondwindracing top alcohol

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    the 4.3 v6 is a small block missing 2 cyl. the weak link on the chevy is head studs and rod angle.more boost will be hard on the heads.years ago I ran a sm blk it ran very hard ran 6's in the 1/4 in a dragster..but never went to many rounds this thing was a maintance nightmare...love my hemi:).Dave
     
    #13
    secondwindracing, Oct 22, 2009

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