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Are 5.56" rods really THAT bad

Discussion in 'The Garage' started by Blazer_Boy, Feb 5, 2003.

  1. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Are 5.56\" rods really THAT bad

    Are the stock 5.56" rods in 400s as bad as everyone gets worked up about. I got my 400 in the shop and started to disassemble it. I was expecting wear city from all the hype, but that was not the case. The odometer showed a little over 100,000 and the bores hardly had any lip to them. You could barely catch your finger on them and the motor had never been overhauled before. For as dirty as the outside was, I suspect regular matience for as clean as the lifter galley was.

    I'm gonna make a 404 (.020 over) that'll run about 400hp on the dyno. The computer shows I'll have that at about 4,700 rpm. Now thats one low winder! If I could keep the stock rods, I could run the stock style pistons. Which means a 9.3:1 squeeze with 64 cc heads and keeping the balance near stock.

    That means no rebalancing, no clearancing, ALOT more affordable, and good compression. You can not find a lower compression hypereucraptic piston for a 5.56" rod, so I gotta run cast. Seeing as how this will be a daily driver, I don't think forged would be in order (cold slap, cost, throwing off balance) and could be fine with cast.

    Basically I wanna build a dependable street engine that I can afford. It'll get clevite bearings, ARP bolts, and that stuff, so its not a total cheapskate special.
     
  2. ZonkRat

    ZonkRat 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    Sounds OK for low RPM motor{under 6000}.One of the main reasons for longer rods is to make more tourqe on bottom and ,but,it actually makes the pistons travel farther,faster with longer stroke.This also lets it draw in and compress more fuel with longer stroke.One of reasons they make nore power.Aftremarket parts are usually stronger too,but,thats not great big deal unless you run it harder. /forums/images/graemlins/crazy.gif /forums/images/graemlins/truck.gifer in TENN. /forums/images/graemlins/thumb.gif
     
  3. Triaged

    Triaged 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    I hate to go against almost everything you said but most of the info is just not correct.

    A short rod will make slightly more low end torque
    A long rod will slightly reduce the accelerations on the piston, cause longer dwell time at TDC and BDC. It will not increase stroke in any way.

    Good aftermarket 5.56 rods are hard to find and cost more than the 5.7. If you were going to replace the rods I would say go with 5.7. If you don't want/need to replace the rods there isn't much wrong with the 5.56 rods. Get them magnafluxed for cracks, shot peened, with some ARP bolts in them and you should be good to go.
     
  4. ZonkRat

    ZonkRat 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    So if I do 383 build on 350 I'll lose bottom end tourqe /forums/images/graemlins/confused.gif
     
  5. ZonkRat

    ZonkRat 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    I was wrong.Had to back up and think bout it.Stroke of crank will change how far and fast piston go.Longer rods don't change speed or travel,moves piston higher in cylinder andreduces side motion of it.I thought longer stroke would make more torque on bottom RPMs. /forums/images/graemlins/crazy.gif /forums/images/graemlins/truck.gifer in TENN. /forums/images/graemlins/thumb.gif
     
  6. m j

    m j 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    cylinder heads is where to spend money not rods.
    long rods are a bandaid to poor flowing cylinder heads.
    many high horsepower engines run short rods.
    if you aer building a restricted rules engine then worry about rod length, for a street motor ignore them and spend money on cylinder heads for power
     
  7. florida4x4

    florida4x4 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    Hi mj! But long rods are more desireable for reducing tendancy of detonation and since the piston is at TDC longer allows the fuel to burn more efficiently. I say put the longest rod in you can afford.
     
  8. DieselDan

    DieselDan 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    The rod/stroke ratio does impact the engine's ability to breathe. The belief that: long-stroke = low RPM torque and short-stroke = high RPM power is actually a distortion of an engines abilty to breath (make power) at a given RPM range. The debate rages as to the amount of benifit gained from long rods. I'm a believer, but I also understand that dyno numbers don't always support this theory.

    As far as piston bore wear on a 400 is concerned; if you have little wear then suspect you have a high nickel content block. IIRC these are marked by a cast in 050 under the timing cover area. /forums/images/graemlins/thumb.gif
     
  9. m j

    m j 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    waste of cash.
    $ for $
    cylinder heads make power
    long rods do nothing
    if you have room and $ for longer rods then you should increase stroke instead

    long rod stuff is myth
     
  10. 4DiggerDan

    4DiggerDan 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    I dunno.. I build a lot of 400's with 5.7" rods. They seem to build lots of power. Of course, the KB "D" cup pistons of the same CC as the OEM piston are a whole different animal. You get away from the 800CC horse trough dish that likes to cause detonation with anything besides late model smogger heads (not enough quench.)

    You can't just swap to a longer rod without having a piston designed for it (the wrist pin must be moved up higher so the piston won't stick out the top of the deck.)

    In case anybody is curious, you figure your rod ratio by dividing the length of rod by length of stroke.
    5.7" divided by 3.750 is 1.52:1
    5.565" divided 3.750 is 1.484:1
    As you can see, both sets of rods suck pretty much equally in this application. Not like a 6" rod in a 327 (1.846:1, or nearing perfection IMHO.) I think it was Smokey Yunick that said it best, "If GM had designed the small block with a 1" taller deck, they would have had the perfect engine"

    How you figure a longer rod is a band-aid for poor flowing heads? If it helps flow with poor flowing heads, won't it still help with better flowing heads?

    I understand that there is such thing as too long a rod ratio. We used a 400 CSB with a 3" stroke crank one time to build an all out buzzbomb one time. It's been a while, but I think it had 6.2" rods (I know the pistons were JE's and the wrist pin was located through the oil control ring.) It had like a 2:1 rod ratio. No matter what we did for heads or cam timing, it never delivered as expected.

    That brings me to my next point... Nobody mentioned how longer rods affect cam timing?? I guess a better way to phrase that is... Nobody mentioned what different demands longer rods place on cam timing..?? I'll give you a hint, if you use the same cam on a heads up dyno test, it'll make the longer rodded engine look marginally better.

    If shorter rods make more torque, then how comes big industrial diesels have John Holmes Signature Series rods??
     
  11. Triaged

    Triaged 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    I'm with mj on this. I would put the money somewhere else. Stock rods can handle a fair amount of power if kept to a reasonable RPM. You won't notice the difference in power from the rods...cylinder heads, stroker crank, roller cam, would all make it on the list befor rods...because I want the most for my money I can get...If I had to buy new rods (because mine were messed up or I was making too much power or spinning the motor too fast) I would get 5.7" rods because they are cheeper for the same quality.
     
  12. m j

    m j 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    How many did you build with 5.56" rods?
    what was the difference in power just in a rod change?
     
  13. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    What about the whole detonation issue with a deep dish pistion? I'm gonna run 64cc vortecs and usually buy 91 gas. I figured the compression ratio using tons of fun little formulas (head gasket thickness, deck clearance, blah, blah, blah) for a squeeze of around 9.25:1. If GM can get those "bad" stock pistons to work on a 58cc 9.2:1 305 that runs on 87, maybe it'll be alright. If I were a wealthy man, I'd have the long rods, different crank, balance job. Maybe some different main caps, see, it just kinda gets out of hand after a while. I don't think all the fancy stuff is need on a low winder. I still want good bolts though, just for cool factor, haha. /forums/images/graemlins/thumb.gif
     
  14. Twiz

    Twiz 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    </font><blockquote><font class="small">In reply to:</font><hr />
    Nobody mentioned how longer rods affect cam timing?? I guess a better way to phrase that is... Nobody mentioned what different demands longer rods place on cam timing..??

    [/ QUOTE ]

    I'll take a shot at that.

    If the piston truley dwells at TDC and BDC longer with the long rods, than that would also mean the piston has to travel faster from TDC to BDC and back again, within the alotted amount of time (RPM).

    So, the Intake Valve Closeing point is even more critical.
    The window of opritunity to fill the chamber becomes narrower.

    If the piston remains at BDC longer, giveing the intake charge longer to fill the cyl. than there should be less of a need to hang the valve open, when compared to the short rod engine. Also, since the piston excellorates faster from BDC, there is more of a chance for the charge to reverse, and flow backwards- back into the intake.

    So if that is the case, I would think with the long rod engine, the intake valve can be closed sooner. Right ?

    Edited:
    *interesting point: closeing the intake-valve early, (in-this case) builds dynamic compression. Which might increase low-end torque... Hmmmmm.. Longs rods for low-end torque ???? Sounds funky, huh ?*


    K- gotta gits before the boss gets back from lunch.
    HeHeHe /forums/images/graemlins/grin.gif
     
  15. florida4x4

    florida4x4 1/2 ton status

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  16. m j

    m j 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    yet most race engines run short rods/deck hieght, unless they are intake restricted. how odd

    NHRA Prostock's run 'big block' deck hieghts shorter then a factory SBC
    SCCA TransAm had Chev cast SBF deck hieght blocks 8.2"
     
  17. florida4x4

    florida4x4 1/2 ton status

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  18. m j

    m j 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    you will get beat by money spent in the right place everytime.
    better induction or more displacement.
    for the motor in question here rods are zero gain items.
     
  19. BorregoK5

    BorregoK5 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    Short Rod is slower at BDC range and faster at TDC range while a Long Rod is faster at BDC range and slower at TDC range. It would lead you to believe a long rod makes more torque and a short rod makes more horsepower..

    Interesting reading?

    http://www.stahlheaders.com/Lit_Rod%20Length.htm
     
  20. Twiz

    Twiz 1/2 ton status

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    Re: Are 5.56\" rods really THAT bad

    Mmmmmmm - shoe leather, I'm kinda aquireing a tast for 'em.
    Allthough I prefer my shoes with a dash of pepper and a pinch of garlic-salt, it really brings out the flavor of aged raw-hide.


    I cought that on one of the other links too, I forgot about the sweep across BDC is longer than the sweep across TDC - totaly screwed me up.
    It would make evertyhing I stated above, just the opposite.

    Um... is it too late to delete that and try it again ?
     

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