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rod comparison

  1. #1
    Junior Member ImOnaBoat's Avatar
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    Default rod comparison

    ive been reading about 460 stock internals and am having a hard time believing that the rods can only handle around 600 horsepower like some people have been saying. i have experience building turbo bmw engines and have made right arround 500 hp on a 2.5 liter with cast crank and factory forged rods and pistons. and i know someone that makes 750 hp at 8000 rpms on the same factory bmw internals.

    while taking out the 460 rods i happened to have a set of the bmw rods and compared them and i dont see why the 460 could handle the same if not more power if turboed and tuned properly.




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    Senior Member earlbrown's Avatar
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    If I had to guess I'd say it's because force increases at the square of mass.....



    .....and I have to think the BMW rod might be made out of better metal.

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    steelcomp was here
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    Quote Originally Posted by ImOnaBoat View Post
    ive been reading about 460 stock internals and am having a hard time believing that the rods can only handle around 600 horsepower like some people have been saying. i have experience building turbo bmw engines and have made right arround 500 hp on a 2.5 liter with cast crank and factory forged rods and pistons. and i know someone that makes 750 hp at 8000 rpms on the same factory bmw internals.

    while taking out the 460 rods i happened to have a set of the bmw rods and compared them and i dont see why the 460 could handle the same if not more power if turboed and tuned properly.



    The "460" rod you're showing isn't a standard rod, it's either a trucck rod or a CJ rod. The standard 429/460 rods are broached at the head of the rod bolt instead of spotfaced which created a shoulder cut across the rod (difficult to explain without showing you) which is a huge stress riser. The rods you are showing are plenty strong for 600hp (and frankly so are the stock ones). With a bolt upgrade and a beam polish/shot pien they're good for plenty more than that.
    FYI...that BMW rod is massive compared to the 460 rod. First off, it's a capscrew rod (instead of a through bolt) and second, look at the cross section of material above the bolt. Look how much thicker the BMW rod is and how much more material there is through that section. That's a huge difference.

    Last edited by scott foxwell; 08-17-2009 at 10:23 PM.
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    Junior Member ImOnaBoat's Avatar
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    i noticed how much thicker the cap was on the bmw. but doesnt the cap strength have to do mostly with rpms and the negative force pulling on the rod rather than the amount of force pushing down on the piston. in theory if you always had a decent amount of positive pressure on the piston you could take the rod cap off completely. i think that most of the failed factory rods are because of n.a. they have to rev higher to make more power where as with F.I. the power is made at lower rpms. just my theory but i guess i will have to test it out.

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    Quote Originally Posted by steelcomp View Post
    The "460" rod you're showing isn't a standard rod, it's either a trucck rod or a CJ rod. The standard 429/460 rods are broached at the head of the rod bolt instead of spotfaced which created a shoulder cut across the rod (difficult to explain without showing you) which is a huge stress riser. The rods you are showing are plenty strong for 600hp (and frankly so are the stock ones). With a bolt upgrade and a beam polish/shot pien they're good for plenty more than that.
    FYI...that BMW rod is massive compared to the 460 rod. First off, it's a capscrew rod (instead of a through bolt) and second, look at the cross section of material above the bolt. Look how much thicker the BMW rod is and how much more material there is through that section. That's a huge difference.


    100% correct....thats why stock turbo porsche internals can run 700 hp at the wheels at 1.4 bar with no problems....

  8. #6
    058
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    The stock Ford rods generally do not break at the thin section or the cap as pointed at in the above pictures. The common place they generally break is mid beam. The only reasonable explanation is fatigue from many cycles. Remember, most of these rods are 30-40 years old with unknown history. I have used the stock CJ/truck rods in twin turboed engines and turned them in the hi 6K-low 7K rpm range and never broke one. I even built an engine using the stock Ford rod bolts and spun that engine 6900-7000 many times, no breakage. This is not to say you will have the same luck as I had and if you are building an engine you are going to lean on hard I would not waste my money and time on a set of rods that can be questionable. As I said in your last thread a set of Eagles is good insurance. The Ford rod will work for you but I would recommend having the rods shot-peened and a good set of rodbolts installed. One more thing I'd like to point out is the difference in material, the stock Ford rod is 1060 mild steel and the Eagle or most other aftermarket rod is 4340 chrome-moly....big difference in strength just in material alone.
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    cfm
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    How about piston speeds and piston/pin/ring weights to name a few more things since it's not all about hp.

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    www.highflowdynamics.com LakesOnly's Avatar
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    Quote Originally Posted by 058 View Post
    The stock Ford rods generally do not break at the thin section or the cap as pointed at in the above pictures. The common place they generally break is mid beam.
    This is correct. Contrary to the older beliefs a D0OE-A CJ rod (with the football-shaped rod bolt) is generally no stronger than the passenger car rod (with the square head-shaped rod bolt), specifically because the rods almost always break mid-beam. In fact, the D0OE-A rod forging can be found either with the spot-faced shoulder (for the football-shaped rod bolt) or machined with the broached shoulder (for the square head-shaped rod bolt), so the rods are essentially the same.

    This is one of those things were the manfuacturer's intentions were in the right place but there was not data gathered as to what the most appropriate upgrade might be. Another example is the D0OE-R CJ heads: a monster of a factory iron head but a complete joke it was for that gargantuan ported cylinder head to be bolted atop a little ol' 429...talk about a mis-match.

    That BMW rod certainly looks beefy relative to the size of the engine and components with which it is associated; imagine how massive the Ford rod would be if it were proportionally as large relative to the 460.

    058 I thought the OEM rods were made of ASE 1053 high carbon steel (same as the 429 steel truck cranks, 100,000 tensile compared to 5140 115,000 tensile & 4340 145,000 tensile) but I'm not 100% positive about that.

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  11. #9
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    scat i beams are cheap

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    058
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    Paul...we are both wrong, SAE 1041 mild steel....At least thats what FoMoCo used in 1969, other years may vary but not likely.
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    gn7
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    Quote Originally Posted by LakesOnly View Post
    Another example is the D0OE-R CJ heads: a monster of a factory iron head but a complete joke it was for that gargantuan ported cylinder head to be bolted atop a little ol' 429...talk about a mis-match.
    LO
    Any more so than say maybe the '69 Boss 302 head? And their fix for that was a small intake valve in '70. Funny what the thought patterns were back then. If it won't flow, make it bigger



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    Quote Originally Posted by gn7 View Post
    Any more so than say maybe the '69 Boss 302 head? And their fix for that was a small intake valve in '70. Funny what the thought patterns were back then. If it won't flow, make it bigger:)devil
    It wasn't only with engineering, it was with materials as well. If a part broke they made it bigger or beefier using the same material. No thought was given to using a stronger material and reducing or at least keeping the weight the same and possibly saving money on forging dies or casting patterns and the related costs of designing and creating new tooling.
    Within the heart of every stray lies the singular desire to be loved. "Good grief you're an irritating blowhard...." [Tex 6/16/11]

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