Rods

Discussion in 'PSI Superchargers Tech Questions' started by Shakedown, Nov 7, 2012.

  1. Shakedown

    Shakedown Jr. Dragster

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    How many passes can you get on a set of GRP rods with L19 bolts in a Pro Mod Hemi? Where only turning around 8600 rpms and 41lbs of boost.
     
    #1
    Shakedown, Nov 7, 2012
  2. Will Hanna

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

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    stroke?

    The bigger the stroke, the harder it is on rods.

    I don't know what the math calc is, but he said the load put on the rod cap goes up exponentially with stroke.

    Let's say you get 20 runs out of a $1100 set of rods = $55 per run.

    Let's say you get 30 runs out of a $1100 set of rods = $36.67 per run.

    I always tell people that rods are pretty damn expensive when they change themselves.

    Years ago I asked Tom Conway how many runs you could get on a set of rods. He replied, "There's only one way to find out and it's pretty expensive."

    Assuming there is no drama, you might be able to get somewhere in the 20's for your combo. I would at very minimum send them back and have them checked at GRP. The tough thing to find is that they tend to crack at the thinnest point from the bolt boss on the cap, which is impossible to inspect without x-ray, or actually cutting the cap in half to inspect. x-ray will probably cost you more than what you are trying to save getting a few more runs.

    It's also a good idea to stretch check the rod bolts when installing to insure you are getting the proper clamping pressure.
     
    #2
    Will Hanna, Nov 7, 2012
  3. wld4x4

    wld4x4 Member

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    How Many Runs?

    First off let me say what I am about to share I do not recomend anyone trying.
    I had a customer running a blown alcohol fontana in a pulling truck with the latest roots blower with no overdrive limits. At mid season when the motor was ready for rods the customer was on a role and didn't want to quit running the motor. I was not in favor of this and explained that he was on his own on the decision to keep running. In the end the motor had a season and a half on it and 75 passes. Now during that time there were no tuning issues or any over reving or drive line breakage. The rod caps were only removed once to check bearings.
    This would be at least 8000 rpm 17 second passes. But nothing went wrong during this time span, but this is a pretty hard core blown deal. They were GRP rods.

    The moral to this is..... I think it is more about what the motor has went through VS how many passes.
    If your banging the blower and knocking out burst panels or over reving due to breakage
    you have to take that into consideration.
     
    #3
    wld4x4, Nov 8, 2012
  4. wld4x4

    wld4x4 Member

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    Rod ratio

    Along with what Will said I also think your rod ratio has more to do with it also, The Fontana/MBR setups tend to have a shorter stroke and bigger bore than most of the standard hemi combos. If your running a 4.5 stroke in a short deck your rod load is going to be worse than a 4.5 crank in a 11.2 deck block.

    Now if you are really pushing one and taking rod caps down and replacing uppers after every pass that is a totaly different deal than I talked about above.
     
    #4
    wld4x4, Nov 8, 2012
  5. Policy Peddler

    Policy Peddler Member

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    Will Hanna

    Will please do not post the cost that way!
    when i multiply that by 4 for my engines it really makes me think the same as my wife, racing is too expensive!!!!

    www.policypeddler.com
     
    #5
    Policy Peddler, Nov 24, 2012

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