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Thread: 5.7 rod 350 piston versus 6.0 rod 350 piston??????

  1. #1
    Junior Member APPRENTICE
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    5.7 rod 350 piston versus 6.0 rod 350 piston??????

    I just bought a set of 5.7 eagle rods and have been looking for pistons, all I really see are .030 pistons for a 6" rod. Sorry for being old school, but whats the reason everyone seems to want the 6" rod. please enlighten me on my ignorance. I will get rid of the rods if its in my best intrest. I do have a .030 350 block and 3.48 crank that I was going to use..... but hell, where do I go from here?
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  2. #2
    Senior Member RACING JUNKIE fla1976's Avatar
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    Here is a very in depth comparison for you.


    http://www.rustpuppy.org/rodstudy.htm

  3. #3
    Member MASTER JOURNEYMAN
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    This could be the beginning of a long discussion.....

    My experience in a 3000 lb drag car shows little difference between 5.7 rods and 6.0 rods. I have turned mine as much as 8K with 5.7 rods and in a like motor with 6.0 rods same cam no difference in ET. The pistons can be found for bores out to 4.060 in Hypereutectic and forged.

  4. #4
    Senior Member RACING JUNKIE fla1976's Avatar
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    I've tried both and saw no difference. A dyno is probably the only way to test it out.

  5. #5
    Senior Member DYNO OPERATOR
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    I read an article by Reher-Morrison about rod length. They wrote that if rod length was put on a priority list it would rank about fiftieth.

    If I had to make a list of the ten most important specifications in a racing engine, connecting rod length would rank about fiftieth. Back in the days when Buddy Morrison and I built dozens of small-block Modified motors, we earnestly believed that an engine needed a 1.9:1 rod/stroke ratio. Today every Pro Stock team uses blocks with super-short deck heights, and we couldnít care less about the rod ratio. A short deck height improves the alignment between the intake manifold runners and the cylinder head intake ports, and helps to stabilize the valvetrain. These are much more important considerations than the rod-to-stroke ratio. Thereís no magic - a rodís function is to connect the piston to the crankshaft. Period.

    TS1955

  6. #6
    Senior Member DYNO OPERATOR
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    Quote Originally Posted by fla1976
    I've tried both and saw no difference. A dyno is probably the only way to test it out.
    Same here. As it was explained to me there is more dwell time at TDC with a 6" rod. creating a more powerfull down stroke. Disclaimer!!!! these are not my words or findings.Just what i was told

  7. #7
    Senior Member EXPERT BUILDER
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    We build a lot of circle track engines and where rules allow we run the longest rod we can, On our 358 2 barrel engines a 6.250 rod over a 5.7 is the way to go.

    On the dyno both the 5.7 and 6.250 make peak power about the same RPM lets say 6800 RPM but at 7500 the 6.250 rod engine will make about 30 horse over the 5.7 rod engine every time.

    The longer rod engines on the dyno seem to have a flater torque curve.

    On our blower engines we use a 6.300 rod in those engines and those have won many championships over the years.
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  8. #8
    Junior Member APPRENTICE
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    Re: 5.7 rod 350 piston versus 6.0 rod 350 piston??????

    Quote Originally Posted by robertstell
    I just bought a set of 5.7 eagle rods and have been looking for pistons, all I really see are .030 pistons for a 6" rod. Sorry for being old school, but whats the reason everyone seems to want the 6" rod. please enlighten me on my ignorance. I will get rid of the rods if its in my best intrest. I do have a .030 350 block and 3.48 crank that I was going to use..... but hell, where do I go from here?
    the 1.724137931 rod ratio (rod/stroke) is not even a factor if over 1.6:1 with the 5.7 rod to 3.48 crank being 1.637931034 you will never see the difference. with the longer rod, you will could have slightly less torque down low because the rod is standing up straighter and will have a little harder time pushing the crank @ lower speeds, thus less torque. but, your longer rod will dwell longer @ tdc and create a little more torque. whether it is usable or not is in the engines design with the heads cam and induction. with a shorter rod, the load will swing a little easier down low but adds a little more load to the blocks cylinder wall. with the longer rod, this loads the crank more. tit for tat,

    you won't see a huge difference unless you are putting this in a mud truck or something very heavy and then that has more to do with proper induction and cam sizing than rod ratio. I have to go with RM here. hp up top has more to do with induction and rod ratio hardly never makes any difference in real power.

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